Merge pull request 'Lidarr: album adds that Lidarr accepts, artist monitoring that sticks' (#138) from dev into main

ArtistResource has no top-level `monitor`. Lidarr reads the choice from
AddOptions (AddArtistOptions, a MonitoringOptions), so the "all"/"future"
we sent there was dropped on deserialisation. AddOptions.Monitor stayed
Unknown, and AlbumMonitoredService.SetAlbumMonitoredStatus returns early
on Unknown. The request's monitoring was never applied.

Send monitor and monitored inside addOptions with searchForMissingAlbums,
the shape Lidarr's getNewArtist.js posts, and set monitorNewItems "all"
explicitly: both choices mean new releases are watched.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitea/workflows/android.yml

@@ -1,92 +0,0 @@
-name: android
-
-# Native Android (Kotlin/Compose/Media3) — M8 rewrite, now the only client.
-# This workflow is testing only — lint + detekt + unit tests on every push
-# to dev/main, plus a debug APK artifact for main. The signed-release
-# build + asset attach + image-bundling lives in release.yml under a
-# `needs:` chain so the docker image cannot ship without the APK.
-
-on:
-  push:
-    branches: [main, dev]
-    paths:
-      - 'android/**'
-      - '.gitea/workflows/android.yml'
-
-# pull_request trigger intentionally omitted — see test-web.yml for
-# the rationale (single-author repo, push covers PR-merge equivalent).
-concurrency:
-  group: ${{ github.workflow }}-${{ github.ref }}
-  cancel-in-progress: true
-
-env:
-  # Silences the JDK 22+ "restricted method in java.lang.System has been
-  # called" warning that Gradle 9.1's bundled native-platform jar trips
-  # at launch (System.load for native primitives). Affects the LAUNCHER
-  # JVM, not the daemon — that's why org.gradle.jvmargs in
-  # gradle.properties isn't enough. Future-compat: required opt-in once
-  # JDK 25 promotes the warning to an error.
-  JAVA_TOOL_OPTIONS: "--enable-native-access=ALL-UNNAMED"
-
-jobs:
-  build:
-    name: Build + lint + test
-    # Using flutter-ci runner label because it's the only proven-working
-    # label with docker that can pull our container.image. Switch to
-    # android-ci once the operator registers that runner label.
-    runs-on: flutter-ci
-    container:
-      image: git.fabledsword.com/bvandeusen/ci-android:36
-
-    defaults:
-      run:
-        working-directory: android
-
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v4
-
-      - name: Cache Gradle dirs
-        # Resolved deps + Gradle distribution + Kotlin daemon caches.
-        # Saves ~3 min per CI run after the first warm-up.
-        uses: actions/cache@v4
-        with:
-          path: |
-            ~/.gradle/caches
-            ~/.gradle/wrapper
-            ~/.kotlin
-          key: gradle-${{ runner.os }}-${{ hashFiles('android/gradle/wrapper/gradle-wrapper.properties', 'android/gradle/libs.versions.toml', 'android/**/*.gradle.kts') }}
-          restore-keys: |
-            gradle-${{ runner.os }}-
-
-      - name: Make gradlew executable
-        run: chmod +x ./gradlew
-
-      - name: Gradle wrapper validation
-        run: ./gradlew --version
-
-      - name: ktlint
-        run: ./gradlew ktlintCheck
-
-      - name: detekt
-        run: ./gradlew detekt
-
-      - name: Unit tests
-        run: ./gradlew testDebugUnitTest
-
-      - name: Assemble debug
-        if: github.event_name == 'push' && github.ref == 'refs/heads/main'
-        run: ./gradlew assembleDebug
-
-      - name: Upload debug APK
-        if: github.event_name == 'push' && github.ref == 'refs/heads/main'
-        # Stock action: it works on this forge since the runner moved to
-        # gitea/runner 3.x, which edits upload-artifact's client-side GHES refusal
-        # out of the action bundle (Scribe snippet #2271). Never @v3 — it reports
-        # success while Gitea serves artifacts back only through the v4 API, and
-        # it is what left 72 unreachable artifacts on this repo (Scribe 2270).
-        uses: actions/upload-artifact@v7
-        with:
-          name: minstrel-android-debug-${{ github.sha }}
-          path: android/app/build/outputs/apk/debug/app-debug.apk
-          if-no-files-found: error

.gitea/workflows/release.yml

@@ -72,9 +72,8 @@ name: release
 # Android APK and uploads it as a workflow artifact. The image-release
 # job declares `needs: android-release`, so the docker image cannot
 # start building until the APK is guaranteed-ready — no polling, no
-# race, no silent-failure mode. Asset attachment to the gitea Release
-# happens in the same android-release job, so the Release-page download
-# link and the in-image bundled APK are both populated atomically.
+# race, no silent-failure mode. Attaching the APK to the gitea Release is
+# its own job (release-assets), behind the test gate below.
 #
 # :latest always carries an APK. Because every main push also moves
 # :latest (not just tags), a main build with no APK would silently strip
@@ -84,8 +83,33 @@ name: release
 # recomputed ones — so no rebuild is needed, just a rebundle. Tag builds
 # keep bundling their own freshly-built APK.
 #
-# Android testing (lint + detekt + unit tests, debug APK upload on main)
-# lives in android.yml and runs independently on every push.
+# THE GATE (rule 177, M462 #4984). Every verifying lane lives in this file —
+# Go (vet, lint, short tests), the Postgres integration suite, the web app
+# (npm audit, svelte-check, vitest), Android (ktlint, detekt, unit tests) and
+# govulncheck — and every job that publishes something names each of them in
+# `needs:` and requires `success` from each, by name. Nothing publishes on red.
+#
+# They used to be three separate workflows (test-go, test-web, android) on the
+# same push trigger as this one. Separate workflows cannot see each other's
+# verdict, so :dev meant "it built", never "it passed": a red test run and a
+# fresh :dev could carry the same timestamp. One graph is the only place the
+# edge can be written.
+#
+# A skipped lane is NOT a pass. The publishing conditions check
+# `result == 'success'` per lane rather than `!failure()`, so a lane that
+# never started blocks the publish exactly as a red one does. Lanes carry no
+# path filters for the same reason: a web-only push still runs the Go suite,
+# because "not run" must never read as "passed".
+#
+# What publishes, and is therefore gated: the image tags (image-release) and
+# the APK + version sidecar attached to a tag's Release (release-assets).
+# android-release only BUILDS the signed APK into a workflow artifact, which
+# nobody outside this run can pull, so it runs in parallel with the lanes
+# instead of after them; attaching it to the Release is the publishing half,
+# and that half waits for the gate.
+#
+# To watch the gate refuse: dispatch this workflow with force_red=true. The go
+# lane fails on purpose, and both publishing jobs must report skipped.
 
 on:
   push:
@@ -95,6 +119,11 @@ on:
       - 'docs/**'
       - '**/*.md'
   workflow_dispatch:
+    inputs:
+      force_red:
+        description: Fail the go lane on purpose, to check that nothing publishes on red
+        type: boolean
+        default: false
 
 # A rapid re-push to main should supersede the in-flight build — the
 # operator explicitly wants the later commit to win. Tags no longer enter
@@ -105,6 +134,269 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
+  # ---------------------------------------------------------------- lanes --
+  # Verifying jobs. Each one is named in the `needs:` of every publishing job
+  # below; add a lane here and it must be added there in the same commit.
+
+  go:
+    runs-on: go-ci
+    container:
+      image: git.fabledsword.com/bvandeusen/ci-go:1.26
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Forced failure (gate check)
+        if: github.event.inputs.force_red == 'true'
+        run: |
+          echo "::error::force_red dispatch: failing on purpose so the publishing jobs must skip"
+          exit 1
+
+      - name: Toolchain versions
+        run: |
+          go version
+          golangci-lint --version
+
+      - name: Generated code matches queries (sqlc)
+        run: make verify-generate
+
+      - name: go vet
+        run: go vet ./...
+
+      - name: golangci-lint
+        run: golangci-lint run ./...
+
+      - name: go test (short, race)
+        run: go test -short -race ./...
+
+  # Full `go test -race` against an ephemeral Postgres.
+  #
+  # DB wiring follows the act_runner shared-daemon pattern: the runner's Docker
+  # daemon also runs the operator's dev compose stack, so service containers
+  # get NO published ports (collision) and no service-name DNS. We discover the
+  # service container through the mounted docker socket and reach it by bridge
+  # IP. The exactly-one assertion is a hard guard — pointing tests at the dev
+  # Postgres would truncate it (the disaster Fable #339 exists to prevent).
+  #
+  # The key stays `integration` with no `name:` (rule 80): act_runner derives
+  # the service container's name from the job's display name.
+  #
+  # `web/build/` has a committed placeholder index.html so go:embed succeeds
+  # without the SPA being built first.
+  integration:
+    runs-on: go-ci
+    container:
+      image: git.fabledsword.com/bvandeusen/ci-go:1.26
+    services:
+      postgres:
+        image: postgres:16-alpine
+        env:
+          POSTGRES_USER: minstrel
+          POSTGRES_PASSWORD: minstrel
+          POSTGRES_DB: minstrel_test
+        # No `ports:` — the runner shares the operator's dev compose
+        # Docker daemon; publishing a fixed host port collides.
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Integration suite (discover service by bridge IP, migrate, test)
+        run: |
+          set -eux
+          # Discover THIS job's Postgres service container via the
+          # mounted docker socket. act_runner attaches the job
+          # container and its service container(s) to a shared per-job
+          # network, so scope discovery to a postgres that sits on a
+          # network THIS job container is also on. The old
+          # `--filter name=integration` matched EVERY concurrent
+          # integration run's postgres (a dev push + the main-merge run
+          # overlap → 2 candidates → false "expected exactly 1" abort).
+          # The operator's dev compose `minstrel-postgres-*` is never on
+          # this job's network; skip it explicitly as belt-and-suspenders
+          # (a wrong target would truncate real data).
+          SELF=$(cat /etc/hostname)
+          SELF_NETS=$(docker inspect -f '{{range $k,$v := .NetworkSettings.Networks}}{{$k}} {{end}}' "$SELF")
+          test -n "$SELF_NETS"
+          echo "self ($SELF) networks: $SELF_NETS"
+          PG_ID=""
+          PG_NAME=""
+          for cid in $(docker ps --filter "ancestor=postgres:16-alpine" -q); do
+            nm=$(docker inspect -f '{{.Name}}' "$cid" | sed 's#^/##')
+            case "$nm" in *minstrel-postgres*|*_postgres_*) continue ;; esac
+            for net in $(docker inspect -f '{{range $k,$v := .NetworkSettings.Networks}}{{$k}} {{end}}' "$cid"); do
+              case " $SELF_NETS " in *" $net "*) PG_ID="$cid"; PG_NAME="$nm"; break 2 ;; esac
+            done
+          done
+          test -n "$PG_ID" || { echo "FATAL: no postgres service container on this job's network (self nets: $SELF_NETS)"; exit 1; }
+          echo "selected postgres: $PG_ID $PG_NAME"
+          PG_IP=$(docker inspect -f '{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' "$PG_ID")
+          test -n "$PG_IP"
+          export MINSTREL_TEST_DATABASE_URL="postgres://minstrel:minstrel@${PG_IP}:5432/minstrel_test?sslmode=disable"
+
+          # Wait for Postgres to accept connections. Asked of the service
+          # container itself: the run: shell is dash (rule 81), where the
+          # old `/dev/tcp` probe never connects and the loop silently
+          # burned its full two minutes on every run.
+          ready=""
+          for i in $(seq 1 60); do
+            if docker exec "$PG_ID" pg_isready -U minstrel -d minstrel_test -q; then ready=1; break; fi
+            sleep 2
+          done
+          test -n "$ready" || { echo "FATAL: postgres never became ready"; exit 1; }
+
+          # Relax durability on the throwaway CI Postgres. Our test pattern
+          # is dbtest.ResetDB → TRUNCATE … RESTART IDENTITY CASCADE before
+          # every test, and the per-TRUNCATE commit fsync is the dominant
+          # cost of the integration suite. The CI DB is rebuilt every run so
+          # fsync / full_page_writes / synchronous_commit buy nothing. Apply
+          # via docker exec because:
+          #  - The act_runner `services:` block can't override the container
+          #    command, so `postgres -c fsync=off` at boot isn't an option.
+          #  - ALTER SYSTEM cannot run inside a transaction; psql -c
+          #    auto-commits each statement, which is what we need.
+          #  - fsync / full_page_writes are sighup GUCs and
+          #    synchronous_commit is user-context, so pg_reload_conf() picks
+          #    all three up with no restart.
+          # Non-fatal: a perms surprise degrades to "slower", never red CI.
+          docker exec "$PG_ID" psql -U minstrel -d minstrel_test \
+            -c "ALTER SYSTEM SET fsync = off" \
+            -c "ALTER SYSTEM SET synchronous_commit = off" \
+            -c "ALTER SYSTEM SET full_page_writes = off" \
+            -c "SELECT pg_reload_conf()" \
+            || echo "WARN: durability relax failed; continuing"
+
+          # Apply embedded migrations to the fresh test DB, then run the
+          # full suite (no -short → integration tests execute). -p 1:
+          # every integration package TRUNCATEs the one shared test DB;
+          # concurrent package binaries → TRUNCATE deadlocks. Serialize
+          # package execution (the documented local invocation too).
+          # -timeout 20m: internal/api alone takes ~6.5 min under -race on
+          # an idle runner, and a dev and a main run sharing the runner
+          # pushed it past go test's default 10m (run 8368, 600.016s, the
+          # running test 2s old — nothing hung).
+          MINSTREL_DATABASE_URL="$MINSTREL_TEST_DATABASE_URL" go run ./cmd/minstrel migrate
+          go test -p 1 -race -timeout 20m ./...
+
+  web:
+    runs-on: go-ci
+    container:
+      image: git.fabledsword.com/bvandeusen/ci-go:1.26
+
+    defaults:
+      run:
+        working-directory: web
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Install deps
+        run: npm ci
+
+      # What ships to browsers: `dependencies` and the runtime they pull in
+      # (svelte, devalue). Build and test tooling (vite, vitest, tailwind,
+      # kit's dev server) is left out because none of it reaches a user, and
+      # its open advisories need major-version upgrades tracked separately.
+      - name: npm audit (shipped dependencies)
+        run: npm audit --omit=dev --audit-level=moderate
+
+      - name: Type-check + svelte-check
+        run: npm run check
+
+      - name: Vitest
+        run: npm test
+
+  android:
+    # Using flutter-ci runner label because it's the only proven-working
+    # label with docker that can pull our container.image.
+    runs-on: flutter-ci
+    container:
+      image: git.fabledsword.com/bvandeusen/ci-android:36
+
+    defaults:
+      run:
+        working-directory: android
+
+    env:
+      # Silences the JDK 22+ "restricted method in java.lang.System has been
+      # called" warning that Gradle's bundled native-platform jar trips at
+      # launch. Affects the LAUNCHER JVM, not the daemon — that's why
+      # org.gradle.jvmargs in gradle.properties isn't enough.
+      JAVA_TOOL_OPTIONS: "--enable-native-access=ALL-UNNAMED"
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Cache Gradle dirs
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.gradle/caches
+            ~/.gradle/wrapper
+            ~/.kotlin
+          key: gradle-${{ runner.os }}-${{ hashFiles('android/gradle/wrapper/gradle-wrapper.properties', 'android/gradle/libs.versions.toml', 'android/**/*.gradle.kts') }}
+          restore-keys: |
+            gradle-${{ runner.os }}-
+
+      - name: Make gradlew executable
+        run: chmod +x ./gradlew
+
+      - name: Gradle wrapper validation
+        run: ./gradlew --version
+
+      - name: ktlint
+        run: ./gradlew ktlintCheck
+
+      - name: detekt
+        run: ./gradlew detekt
+
+      - name: Unit tests
+        run: ./gradlew testDebugUnitTest
+
+      # No debug APK is built or uploaded here. Main used to upload a
+      # debug-signed app-debug.apk: a build signed by a key regenerated in
+      # every container, which no install can update (family idea #5103,
+      # practice 2). Phones get builds from android-release, signed with
+      # the one release key, on dev and on tags.
+
+  # Known vulnerabilities in the Go code and the standard library it is built
+  # with. Runs in the SAME image the Dockerfile's builder stage uses, so the
+  # standard library it checks is the one that ends up in the shipped binary;
+  # the ci-go image carries its own Go and would be checking a different
+  # toolchain. Keep this image and the Dockerfile's builder in step.
+  #
+  # govulncheck is fetched at CI time, unpinned (rule 154): the vulnerability
+  # database and the tool that reads it should both be current.
+  govulncheck:
+    runs-on: go-ci
+    container:
+      image: golang:1.26-bookworm
+
+    steps:
+      # Plain git, not actions/checkout: that action runs on node, which the
+      # golang image does not carry. This step is dash (rule 81).
+      - name: Checkout
+        env:
+          TOKEN: ${{ github.token }}
+        run: |
+          set -eu
+          auth=$(printf 'x-access-token:%s' "$TOKEN" | base64 -w0)
+          git init -q .
+          git remote add origin "${{ github.server_url }}/${{ github.repository }}.git"
+          git -c http.extraHeader="Authorization: Basic ${auth}" fetch -q --depth 1 origin "${{ github.sha }}"
+          git checkout -q FETCH_HEAD
+          git log -1 --format='%H %s'
+
+      - name: govulncheck
+        run: |
+          go version
+          go run golang.org/x/vuln/cmd/govulncheck@latest ./...
+
+  # ------------------------------------------------------------ artifacts --
+
   android-release:
     name: Build signed APK (releases and dev)
     # Also builds on `dev`, which is what makes a test channel possible at
@@ -231,6 +523,42 @@ jobs:
             -PMINSTREL_VERSION_NAME=${{ steps.ver.outputs.name }} \
             -PMINSTREL_VERSION_CODE=${{ steps.ver.outputs.code }}
 
+      # The APK every phone updates from must carry THE release key: Android
+      # updates an app in place only when the signer matches, so an APK
+      # signed by any other key (debug, a regenerated keystore, a swapped
+      # secret) reaches no installed phone. The certificate's digest is
+      # pinned below; it is public, not a secret. Gradle signs with the
+      # release key or leaves the APK unsigned, and an unsigned build fails
+      # here too, as there is no app-release.apk to verify (family idea
+      # #5103, practice 3). apksigner, not keytool: keytool prints nothing
+      # for a v2-only APK.
+      #
+      # Rotating the key on purpose means every install must be removed and
+      # reinstalled; change the digest here in the same commit.
+      - name: The APK carries the release key
+        shell: bash
+        env:
+          # CN=Minstrel, O=FabledSword. Read from run 8446 (#5116).
+          RELEASE_CERT_SHA256: 43d183307bc46b821789d90444a960b137f78f2166ff431efb2406d0fceaf612
+        run: |
+          set -euo pipefail
+          sdk="${ANDROID_HOME:-${ANDROID_SDK_ROOT:-}}"
+          signer="$(ls "$sdk"/build-tools/*/apksigner 2>/dev/null | sort -V | tail -1 || true)"
+          test -n "$signer" || { echo "::error::no apksigner under '$sdk/build-tools'"; exit 1; }
+          certs="$("$signer" verify --print-certs app/build/outputs/apk/release/app-release.apk)"
+          printf '%s\n' "$certs" | grep -E '^Signer #[0-9]+ certificate (DN|SHA-256 digest)'
+          # One signer, and it is ours. A second signer would be a lineage or
+          # a mistake; either way not something to ship unexamined.
+          digests="$(printf '%s\n' "$certs" | sed -n 's/^Signer #[0-9]* certificate SHA-256 digest: //p')"
+          if [ "$digests" != "$RELEASE_CERT_SHA256" ]; then
+            if printf '%s' "$certs" | grep -q 'CN=Android Debug'; then
+              echo "::error::the release APK is signed with a debug key"
+            else
+              echo "::error::the release APK is not signed by the release key: got '${digests//$'\n'/ }', want ${RELEASE_CERT_SHA256}"
+            fi
+            exit 1
+          fi
+
       - name: Upload APK as workflow artifact
         # Stock action (snippet #2271) — never @v3, which uploads something Gitea
         # will never serve back. This is the producing half of a pair:
@@ -245,21 +573,47 @@ jobs:
           # artifact existing, so an empty upload must fail here, not there.
           if-no-files-found: error
 
+  # Publishes the signed APK and its version sidecar on the tag's Release.
+  # Split out of android-release so the APK can be BUILT in parallel with the
+  # lanes while being PUBLISHED only once they have all passed.
+  release-assets:
+    name: Attach APK to the Release (tag releases only)
+    needs: [go, integration, web, android, govulncheck, android-release]
+    if: >-
+      ${{
+      !cancelled()
+      && needs.go.result == 'success'
+      && needs.integration.result == 'success'
+      && needs.web.result == 'success'
+      && needs.android.result == 'success'
+      && needs.govulncheck.result == 'success'
+      && needs.android-release.result == 'success'
+      && startsWith(github.ref, 'refs/tags/v') }}
+    runs-on: go-ci
+    container:
+      image: git.fabledsword.com/bvandeusen/ci-go:1.26
+
+    steps:
+      - name: Download signed APK artifact
+        uses: actions/download-artifact@v8
+        with:
+          name: minstrel-apk
+          path: release-apk/
+
       - name: Attach APK to gitea Release
         # Tag releases only. A dev build has no Release to hang assets on and
         # does not need one — the :dev image bundles the APK, and the server
         # serves it from /api/client/apk like any other.
-        if: startsWith(github.ref, 'refs/tags/v')
         shell: bash
         env:
           CI_TOKEN: ${{ secrets.CI_TOKEN }}
-          VERSION_NAME: ${{ steps.ver.outputs.name }}
-          VERSION_CODE: ${{ steps.ver.outputs.code }}
+          VERSION_NAME: ${{ needs.android-release.outputs.version_name }}
+          VERSION_CODE: ${{ needs.android-release.outputs.version_code }}
         run: |
           set -euxo pipefail
           TAG="${GITHUB_REF#refs/tags/}"
           REPO="${GITHUB_REPOSITORY}"
-          APK_PATH="app/build/outputs/apk/release/app-release.apk"
+          APK_PATH="release-apk/app-release.apk"
           ls -lh "${APK_PATH}"
 
           # Publish the version sidecar as a release asset next to the APK.
@@ -313,13 +667,21 @@ jobs:
 
   image-release:
     name: Build + push container image
-    # `needs:` waits for android-release. For tag pushes android-release
-    # runs and must succeed before this job starts — guaranteeing the
-    # APK artifact is present. For main pushes android-release is
-    # skipped; the `if: ...` below lets this job run anyway and the
-    # download/copy steps gate themselves on the tag context.
-    needs: [android-release]
-    if: ${{ !failure() && !cancelled() }}
+    # Every lane must have SUCCEEDED, each named here (rule 177). Then the
+    # APK: tag and dev pushes build one and it must have succeeded; main
+    # pushes skip android-release and bundle the latest release's APK
+    # instead, so for main alone a skipped android-release is expected.
+    needs: [go, integration, web, android, govulncheck, android-release]
+    if: >-
+      ${{
+      !cancelled()
+      && needs.go.result == 'success'
+      && needs.integration.result == 'success'
+      && needs.web.result == 'success'
+      && needs.android.result == 'success'
+      && needs.govulncheck.result == 'success'
+      && (needs.android-release.result == 'success'
+      || (needs.android-release.result == 'skipped' && github.ref == 'refs/heads/main')) }}
     runs-on: go-ci
     container:
       image: git.fabledsword.com/bvandeusen/ci-go:1.26
@@ -528,8 +890,13 @@ jobs:
 
       - name: Build and push
         if: steps.guard.outputs.ready == 'true'
+        # --pull: the Dockerfile's base images are floating tags (golang:1.26,
+        # debian:bookworm-slim). Without it the runner's daemon reuses
+        # whatever it cached, and the shipped binary can sit on a Go patch
+        # release govulncheck already flagged while the lane, which pulls
+        # fresh, reports clean.
         run: |
-          docker buildx build \
+          docker buildx build --pull \
             --build-arg MINSTREL_VERSION="${{ steps.tags.outputs.version }}" \
             --build-arg MINSTREL_CHANNEL="${{ steps.tags.outputs.channel }}" \
             --push ${{ steps.tags.outputs.args }} .
@@ -554,7 +921,7 @@ jobs:
   # above did NOT succeed.
   verify-release:
     name: Verify release artifacts (tag releases only)
-    needs: [android-release, image-release]
+    needs: [android-release, release-assets, image-release]
     if: ${{ always() && startsWith(github.ref, 'refs/tags/v') }}
     runs-on: go-ci
     container:

.gitea/workflows/test-go.yml

@@ -1,156 +0,0 @@
-name: test-go
-
-# Go server: vet + golangci-lint + short race tests. Runs on push to
-# dev/main and PRs to main, scoped to Go-side files only — web-only or
-# Flutter-only diffs don't trigger this workflow.
-#
-# Two jobs: `test` (fast — vet + lint + `go test -short -race`, no DB) and
-# `integration` (full `go test -race` against an ephemeral Postgres).
-#
-# Integration-job DB wiring follows the act_runner shared-daemon pattern:
-# the runner's Docker daemon also runs the operator's dev compose stack,
-# so service containers get NO published ports (collision) and no
-# service-name DNS. We discover the service container by the job-scoped
-# name filter via the mounted docker socket and reach it by bridge IP.
-# The exactly-one assertion is a hard guard — pointing tests at the dev
-# Postgres would truncate it (the disaster Fable #339 exists to prevent).
-#
-# `web/build/` has a committed placeholder index.html so go:embed succeeds
-# without needing the SPA to be freshly built. Real builds happen in
-# release.yml (container) and locally during dev.
-
-on:
-  push:
-    branches: [dev, main]
-    paths:
-      - '**/*.go'
-      - 'go.mod'
-      - 'go.sum'
-      - 'sqlc.yaml'
-      - 'Makefile'
-      - 'internal/**'
-      - 'cmd/**'
-      - '.golangci.yml'
-      - '.gitea/workflows/test-go.yml'
-      # The release lane's own trigger is `main` + tags, so nothing it
-      # contains is exercised until a release is already running. These two
-      # entries are what let internal/server/release_version_test.go guard
-      # the version derivation on ordinary dev pushes instead.
-      - 'ci/**'
-      - '.gitea/workflows/release.yml'
-
-# pull_request trigger intentionally omitted — see test-web.yml for
-# the rationale (single-author repo, push covers PR-merge equivalent).
-concurrency:
-  group: ${{ github.workflow }}-${{ github.ref }}
-  cancel-in-progress: true
-
-jobs:
-  test:
-    runs-on: go-ci
-    container:
-      image: git.fabledsword.com/bvandeusen/ci-go:1.26
-
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v4
-
-      - name: Toolchain versions
-        run: |
-          go version
-          golangci-lint --version
-
-      - name: Generated code matches queries (sqlc)
-        run: make verify-generate
-
-      - name: go vet
-        run: go vet ./...
-
-      - name: golangci-lint
-        run: golangci-lint run ./...
-
-      - name: go test (short, race)
-        run: go test -short -race ./...
-
-  integration:
-    runs-on: go-ci
-    container:
-      image: git.fabledsword.com/bvandeusen/ci-go:1.26
-    services:
-      postgres:
-        image: postgres:16-alpine
-        env:
-          POSTGRES_USER: minstrel
-          POSTGRES_PASSWORD: minstrel
-          POSTGRES_DB: minstrel_test
-        # No `ports:` — the runner shares the operator's dev compose
-        # Docker daemon; publishing a fixed host port collides.
-
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v4
-
-      - name: Integration suite (discover service by bridge IP, migrate, test)
-        run: |
-          set -eux
-          # Discover THIS job's Postgres service container via the
-          # mounted docker socket. act_runner attaches the job
-          # container and its service container(s) to a shared per-job
-          # network, so scope discovery to a postgres that sits on a
-          # network THIS job container is also on. The old
-          # `--filter name=integration` matched EVERY concurrent
-          # integration run's postgres (a dev push + the main-merge run
-          # overlap → 2 candidates → false "expected exactly 1" abort).
-          # The operator's dev compose `minstrel-postgres-*` is never on
-          # this job's network; skip it explicitly as belt-and-suspenders
-          # (a wrong target would truncate real data).
-          SELF=$(cat /etc/hostname)
-          SELF_NETS=$(docker inspect -f '{{range $k,$v := .NetworkSettings.Networks}}{{$k}} {{end}}' "$SELF")
-          test -n "$SELF_NETS"
-          echo "self ($SELF) networks: $SELF_NETS"
-          PG_ID=""
-          PG_NAME=""
-          for cid in $(docker ps --filter "ancestor=postgres:16-alpine" -q); do
-            nm=$(docker inspect -f '{{.Name}}' "$cid" | sed 's#^/##')
-            case "$nm" in *minstrel-postgres*|*_postgres_*) continue ;; esac
-            for net in $(docker inspect -f '{{range $k,$v := .NetworkSettings.Networks}}{{$k}} {{end}}' "$cid"); do
-              case " $SELF_NETS " in *" $net "*) PG_ID="$cid"; PG_NAME="$nm"; break 2 ;; esac
-            done
-          done
-          test -n "$PG_ID" || { echo "FATAL: no postgres service container on this job's network (self nets: $SELF_NETS)"; exit 1; }
-          echo "selected postgres: $PG_ID $PG_NAME"
-          PG_IP=$(docker inspect -f '{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' "$PG_ID")
-          test -n "$PG_IP"
-          export MINSTREL_TEST_DATABASE_URL="postgres://minstrel:minstrel@${PG_IP}:5432/minstrel_test?sslmode=disable"
-
-          # Wait for Postgres to accept TCP (no health-check dependency).
-          for i in $(seq 1 60); do (echo > "/dev/tcp/${PG_IP}/5432") 2>/dev/null && break; sleep 2; done
-
-          # Relax durability on the throwaway CI Postgres. Our test pattern
-          # is dbtest.ResetDB → TRUNCATE … RESTART IDENTITY CASCADE before
-          # every test, and the per-TRUNCATE commit fsync is the dominant
-          # cost of the integration suite. The CI DB is rebuilt every run so
-          # fsync / full_page_writes / synchronous_commit buy nothing. Apply
-          # via docker exec because:
-          #  - The act_runner `services:` block can't override the container
-          #    command, so `postgres -c fsync=off` at boot isn't an option.
-          #  - ALTER SYSTEM cannot run inside a transaction; psql -c
-          #    auto-commits each statement, which is what we need.
-          #  - fsync / full_page_writes are sighup GUCs and
-          #    synchronous_commit is user-context, so pg_reload_conf() picks
-          #    all three up with no restart.
-          # Non-fatal: a perms surprise degrades to "slower", never red CI.
-          docker exec "$PG_ID" psql -U minstrel -d minstrel_test \
-            -c "ALTER SYSTEM SET fsync = off" \
-            -c "ALTER SYSTEM SET synchronous_commit = off" \
-            -c "ALTER SYSTEM SET full_page_writes = off" \
-            -c "SELECT pg_reload_conf()" \
-            || echo "WARN: durability relax failed; continuing"
-
-          # Apply embedded migrations to the fresh test DB, then run the
-          # full suite (no -short → integration tests execute). -p 1:
-          # every integration package TRUNCATEs the one shared test DB;
-          # concurrent package binaries → TRUNCATE deadlocks. Serialize
-          # package execution (the documented local invocation too).
-          MINSTREL_DATABASE_URL="$MINSTREL_TEST_DATABASE_URL" go run ./cmd/minstrel migrate
-          go test -p 1 -race ./...

.gitea/workflows/test-web.yml

@@ -1,44 +0,0 @@
-name: test-web
-
-# Web SPA: vitest + svelte-check. Runs on push to dev/main only —
-# the `pull_request` trigger is intentionally omitted because every
-# branch on this repo is local-only (no fork PRs), so the dev push
-# fully covers what a PR run would re-execute. Keeping both events
-# doubled CI cost on every commit.
-
-on:
-  push:
-    branches: [dev, main]
-    paths:
-      - 'web/**'
-      - '.gitea/workflows/test-web.yml'
-
-# Cancel an earlier in-flight run for the same ref when a newer
-# commit arrives. With cancel-in-progress, rapid re-pushes don't
-# pile up zombie runs.
-concurrency:
-  group: ${{ github.workflow }}-${{ github.ref }}
-  cancel-in-progress: true
-
-jobs:
-  test:
-    runs-on: go-ci
-    container:
-      image: git.fabledsword.com/bvandeusen/ci-go:1.26
-
-    defaults:
-      run:
-        working-directory: web
-
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v4
-
-      - name: Install deps
-        run: npm ci
-
-      - name: Type-check + svelte-check
-        run: npm run check
-
-      - name: Vitest
-        run: npm test

Dockerfile

@@ -7,7 +7,7 @@ RUN npm ci
 COPY web/ ./
 RUN npm run build
 
-FROM golang:1.25-bookworm AS builder
+FROM golang:1.26-bookworm AS builder
 WORKDIR /src
 COPY go.mod go.sum ./
 RUN go mod download
@@ -33,8 +33,14 @@ RUN go build -trimpath \
     -o /out/minstrel ./cmd/minstrel
 
 FROM debian:bookworm-slim
+# ffmpeg: duration probes and the exact-tier audio hash (a SHA-256 of the
+# encoded audio packets, so no decode). libchromaprint-tools: fpcalc, the
+# acoustic fingerprint that tells the same recording at two bitrates apart
+# from two different recordings (M400). Both are baked in at build time so a
+# deployed instance never fetches either (rule 164); fpcalc is shelled out
+# rather than bound because CGO_ENABLED=0 above rules out cgo.
 RUN apt-get update \
-    && apt-get install -y --no-install-recommends ca-certificates ffmpeg \
+    && apt-get install -y --no-install-recommends ca-certificates ffmpeg libchromaprint-tools \
     && rm -rf /var/lib/apt/lists/*
 
 RUN groupadd --system --gid 1000 minstrel \

README.md

@@ -34,11 +34,18 @@ Minstrel is not affiliated with or endorsed by Lidarr, ListenBrainz, MusicBrainz
 services:
   minstrel:
     image: git.fabledsword.com/bvandeusen/minstrel:latest
+    # Reachable from your LAN at http://<host>:4533. If this host faces the
+    # internet, bind it to 127.0.0.1 and put an HTTPS proxy in front instead:
+    # see docs/hosting.md.
     ports: ['4533:4533']
     volumes:
       # Your music library. Point ./music at wherever your audio files
-      # live. Mounted read-only — Minstrel never writes to your library.
-      - ./music:/music:ro
+      # live. Writable, because Minstrel deletes a file when an admin asks
+      # it to (for example, quarantine's "Delete file"). It never moves,
+      # renames or retags anything. The container runs as uid 1000, so that
+      # user needs write access to the folders. Mount it :ro to forbid even
+      # deletes: those actions then refuse, say why, and delete nothing.
+      - ./music:/music
       # Generated data: playlist cover collages, artist art, caches.
       # The path must match MINSTREL_STORAGE_DATA_DIR, which the image
       # sets to /app/data — keep this mount on /app/data or your cache
@@ -47,7 +54,7 @@ services:
     environment:
       MINSTREL_DATABASE_URL: postgres://minstrel:minstrel@db:5432/minstrel?sslmode=disable
       # Colon-separated library roots to scan; must match the container
-      # path of the read-only music mount above (/music here).
+      # path of the music mount above (/music here).
       MINSTREL_LIBRARY_SCAN_PATHS: /music
     depends_on: [db]
 
@@ -72,9 +79,9 @@ docker compose up -d
 
 ## First run
 
-With the stack up, a handful of in-app steps get you to a working library. Use your own host in place of `localhost` if you're reaching the server over a LAN/VPN address (plain `http://` is fine — no TLS required).
+With the stack up, a handful of in-app steps get you to a working library. Use your own host in place of `localhost` if you're reaching the server over a LAN/VPN address. Plain `http://` is fine on a network you trust; a server reachable from the internet belongs behind HTTPS, which [docs/hosting.md](docs/hosting.md) walks through.
 
-**1. Create your admin account.** Visit `http://localhost:4533/register`. The first account on a fresh instance is automatically the administrator; later users join through the same form or an invite token (step 5).
+**1. Create your admin account.** Visit `http://localhost:4533/register`. The first account on a fresh instance becomes the administrator, and creating it asks for the **setup token** the server prints in its log (`docker compose logs minstrel | grep setup_token`), so nobody else can claim a newly exposed server first. Later users join through the same form or an invite token (step 5).
 
 <a href="docs/screenshots/register.png"><img src="docs/screenshots/register.png" width="320" alt="Creating the first (admin) account on a fresh instance"></a>
 
@@ -96,6 +103,8 @@ With the stack up, a handful of in-app steps get you to a working library. Use y
 
 For the full configuration surface, see [`config.example.yaml`](./config.example.yaml).
 
+Hosting Minstrel on the internet: see [docs/hosting.md](docs/hosting.md). What Minstrel does to protect accounts, and why: [docs/security.md](docs/security.md).
+
 ## Configuration
 
 Most operators only need the env vars in the quickstart above. A few extras worth knowing:
@@ -150,7 +159,8 @@ Two concurrent dev processes:
   truncates your dev `minstrel` data (admin user, library, likes). It
   brings up the compose Postgres and creates the test DB if missing.
 - CI runs both: a fast `go test -short -race` gate plus an integration
-  job with its own ephemeral Postgres (`.gitea/workflows/test-go.yml`).
+  job with its own ephemeral Postgres (the `integration` lane in
+  `.gitea/workflows/release.yml`, which also gates every image publish).
 
 ### Production build
 

android/app/build.gradle.kts

@@ -72,9 +72,13 @@ android {
                 getDefaultProguardFile("proguard-android-optimize.txt"),
                 "proguard-rules.pro",
             )
+            // Signed with the release key or not at all. Falling back to the
+            // debug key made a missing secret into a published APK that no
+            // install could ever update (family idea #5103, practice 2). An
+            // unsigned build installs nowhere, so the gap shows at once.
             signingConfig =
                 if (System.getenv("ANDROID_KEYSTORE_PATH").isNullOrEmpty()) {
-                    signingConfigs.getByName("debug")
+                    null
                 } else {
                     signingConfigs.getByName("release")
                 }

android/app/src/main/java/com/fabledsword/minstrel/admin/ui/AdminQuarantineScreen.kt

@@ -15,10 +15,14 @@ import androidx.compose.material3.HorizontalDivider
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.OutlinedButton
 import androidx.compose.material3.Scaffold
+import androidx.compose.material3.SnackbarHost
+import androidx.compose.material3.SnackbarHostState
 import androidx.compose.material3.Text
 import androidx.compose.material3.TextButton
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.getValue
+import androidx.compose.runtime.remember
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.text.style.TextOverflow
@@ -42,6 +46,12 @@ fun AdminQuarantineScreen(
     viewModel: AdminQuarantineViewModel = hiltViewModel(),
 ) {
     val state by viewModel.uiState.collectAsStateWithLifecycle()
+    val snackbarHostState = remember { SnackbarHostState() }
+    LaunchedEffect(Unit) {
+        viewModel.transientMessages.collect { msg ->
+            snackbarHostState.showSnackbar(msg)
+        }
+    }
     Scaffold(
         contentWindowInsets = ShellContentWindowInsets,
         modifier = Modifier.fillMaxSize(),
@@ -53,6 +63,7 @@ fun AdminQuarantineScreen(
                 onBack = { navController.popBackStack() },
             )
         },
+        snackbarHost = { SnackbarHost(snackbarHostState) },
     ) { inner ->
         PullToRefreshScaffold(
             onRefresh = { viewModel.refresh().join() },

android/app/src/main/java/com/fabledsword/minstrel/admin/ui/AdminQuarantineViewModel.kt

@@ -10,10 +10,13 @@ import com.fabledsword.minstrel.events.EventsStream
 import com.fabledsword.minstrel.models.AdminQuarantineItemRef
 import dagger.hilt.android.lifecycle.HiltViewModel
 import kotlinx.coroutines.Job
+import kotlinx.coroutines.channels.Channel
+import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.asStateFlow
 import kotlinx.coroutines.flow.filter
+import kotlinx.coroutines.flow.receiveAsFlow
 import kotlinx.coroutines.launch
 import javax.inject.Inject
 
@@ -34,6 +37,15 @@ class AdminQuarantineViewModel @Inject constructor(
     private val internal = MutableStateFlow<AdminQuarantineUiState>(AdminQuarantineUiState.Loading)
     val uiState: StateFlow<AdminQuarantineUiState> = internal.asStateFlow()
 
+    /**
+     * One-shot messages for the screen's snackbar. A failed action has to say
+     * why: the row quietly reappearing reads as a glitch, and for a Delete
+     * file refused by a read-only library it hides the one thing the
+     * operator can fix (#3918).
+     */
+    private val transientMessagesChannel = Channel<String>(Channel.BUFFERED)
+    val transientMessages: Flow<String> = transientMessagesChannel.receiveAsFlow()
+
     init {
         refresh()
         viewModelScope.launch {
@@ -86,8 +98,9 @@ class AdminQuarantineViewModel @Inject constructor(
             try {
                 action(trackId)
             } catch (
-                @Suppress("TooGenericExceptionCaught", "SwallowedException") e: Throwable,
+                @Suppress("TooGenericExceptionCaught") e: Throwable,
             ) {
+                transientMessagesChannel.trySend(ErrorCopy.fromThrowable(e))
                 refresh()
             }
         }

android/app/src/main/java/com/fabledsword/minstrel/api/BaseUrlInterceptor.kt

@@ -50,7 +50,14 @@ class BaseUrlInterceptor @Inject constructor(
                 .port(baseUrl.port)
                 .build()
         } ?: original.url
-        return chain.proceed(original.newBuilder().url(rewritten).build())
+        return chain.proceed(
+            original.newBuilder()
+                .url(rewritten)
+                // Lets CleartextGuardInterceptor tell server requests from
+                // external fetches once the placeholder host is gone.
+                .tag(MinstrelServerRequest::class.java, MinstrelServerRequest)
+                .build(),
+        )
     }
 
     companion object {

android/app/src/main/java/com/fabledsword/minstrel/api/CleartextGuard.kt

@@ -0,0 +1,84 @@
+package com.fabledsword.minstrel.api
+
+import okhttp3.Interceptor
+import okhttp3.Response
+import java.io.IOException
+import java.net.Inet4Address
+import java.net.Inet6Address
+import java.net.InetAddress
+
+/**
+ * Marks a request as bound for the Minstrel server, set by
+ * [BaseUrlInterceptor] when it retargets the placeholder host. Those are the
+ * requests that carry the session cookie and the password.
+ */
+object MinstrelServerRequest
+
+/**
+ * Plain `http://` to the Minstrel server is allowed only when the connection
+ * actually lands on a private address (family security baseline #5105,
+ * practice 13).
+ *
+ * Cleartext stays permitted app-wide for LAN servers and UPnP
+ * (network_security_config.xml, #2439), but a password or session cookie sent
+ * over plain HTTP to a public address can be read by anyone on the path.
+ *
+ * Checked per connection, on the address the socket really reached, not on
+ * the URL when it was typed: a name that resolved to the home network when it
+ * was entered resolves to a public address once the phone leaves home, and
+ * that is exactly when the password would go out in the clear. A network
+ * interceptor runs after the connection is made and before any request byte
+ * is written, so nothing is sent.
+ */
+class CleartextGuardInterceptor(
+    // The policy is a parameter so a test can refuse loopback, the only
+    // address a test server can listen on.
+    private val allows: (InetAddress) -> Boolean = CleartextPolicy::allows,
+) : Interceptor {
+    override fun intercept(chain: Interceptor.Chain): Response {
+        val request = chain.request()
+        if (request.isHttps || request.tag(MinstrelServerRequest::class.java) == null) {
+            return chain.proceed(request)
+        }
+        val address = chain.connection()?.route()?.socketAddress?.address
+        if (address != null && !allows(address)) {
+            throw CleartextToPublicHostException(request.url.host)
+        }
+        return chain.proceed(request)
+    }
+}
+
+/** The server was reached over plain HTTP at a public address, and refused. */
+class CleartextToPublicHostException(host: String) :
+    IOException("refusing plain http:// to $host: it is a public address")
+
+/** Which addresses plain HTTP may reach: the home network, never the internet. */
+object CleartextPolicy {
+    private const val CGNAT_FIRST_OCTET = 100
+    private const val CGNAT_SECOND_MASK = 0xC0
+    private const val CGNAT_SECOND_PREFIX = 64
+    private const val ULA_MASK = 0xFE
+    private const val ULA_PREFIX = 0xFC
+    private const val BYTE = 0xFF
+
+    fun allows(address: InetAddress): Boolean =
+        address.isLoopbackAddress ||
+            address.isSiteLocalAddress || // 10/8, 172.16/12, 192.168/16
+            address.isLinkLocalAddress || // 169.254/16, fe80::/10
+            address.isAnyLocalAddress ||
+            isCarrierGradeNat(address) ||
+            isUniqueLocal(address)
+
+    // 100.64/10. Tailscale and other overlay VPNs hand these out; the overlay
+    // encrypts the traffic itself.
+    private fun isCarrierGradeNat(address: InetAddress): Boolean {
+        if (address !is Inet4Address) return false
+        val b = address.address
+        return (b[0].toInt() and BYTE) == CGNAT_FIRST_OCTET &&
+            (b[1].toInt() and CGNAT_SECOND_MASK) == CGNAT_SECOND_PREFIX
+    }
+
+    // fc00::/7, IPv6's private range.
+    private fun isUniqueLocal(address: InetAddress): Boolean =
+        address is Inet6Address && (address.address[0].toInt() and ULA_MASK) == ULA_PREFIX
+}

android/app/src/main/java/com/fabledsword/minstrel/api/ErrorCopy.kt

@@ -37,18 +37,36 @@ object ErrorCopy {
      * as connection failures.
      */
     fun fromThrowable(t: Throwable): String = when (t) {
-        is HttpException -> messageFor(codeFromHttp(t))
+        is HttpException -> fromHttp(t)
+        is CleartextToPublicHostException -> messageFor("cleartext_public")
         is IOException -> messageFor("connection_refused")
         else -> TABLE.getValue("unknown")
     }
 
-    private fun codeFromHttp(e: HttpException): String {
+    /**
+     * Codes whose server message carries specifics the operator needs in
+     * order to act — which directory, which uid — that fixed copy cannot say.
+     * For these the message follows the copy (#3918). Kept to a named set on
+     * purpose: most server messages are internal detail. Mirrors web's
+     * errors.ts.
+     */
+    private val DETAIL_CODES = setOf("library_not_writable", "file_delete_failed")
+
+    private fun fromHttp(e: HttpException): String {
+        val body = bodyFromHttp(e)
+        val copy = messageFor(body.code.ifEmpty { "unknown" })
+        return if (body.code in DETAIL_CODES && body.message.isNotBlank()) {
+            "$copy ${body.message}"
+        } else {
+            copy
+        }
+    }
+
+    private fun bodyFromHttp(e: HttpException): Body {
         val raw = runCatching { e.response()?.errorBody()?.string() }.getOrNull()
-            ?: return "unknown"
-        val code = runCatching { json.decodeFromString<Envelope>(raw).error?.code }
-            .getOrNull()
-            .orEmpty()
-        return code.ifEmpty { "unknown" }
+            ?: return Body()
+        return runCatching { json.decodeFromString<Envelope>(raw).error }
+            .getOrNull() ?: Body()
     }
 
     private val TABLE: Map<String, String> = mapOf(
@@ -58,6 +76,7 @@ object ErrorCopy {
         "forbidden" to "You don't have permission to do that.",
         "not_authorized" to "You don't have permission to do that.",
         "invalid_credentials" to "Wrong username or password.",
+        "rate_limited" to "Too many attempts. Wait a few minutes and try again.",
         "wrong_password" to "Current password is incorrect.",
         "password_too_short" to "Password must be at least 8 characters.",
         "username_invalid" to "That username isn't valid.",
@@ -83,6 +102,9 @@ object ErrorCopy {
         "mbid_required" to "An MBID is required for this lookup.",
         "system_playlist_readonly" to "System playlists can't be edited directly.",
         "connection_refused" to "Couldn't reach the server. Check the URL and try again.",
+        "cleartext_public" to
+            "This server is on the internet, so its URL must start with https://. " +
+            "Plain http:// only works on your home network.",
         "lidarr_unreachable" to
             "Lidarr is unreachable right now. Try again, or check Admin → Integrations.",
         "lidarr_disabled" to "Lidarr integration is not enabled.",
@@ -99,6 +121,8 @@ object ErrorCopy {
         "request_not_pending" to "This request is no longer pending.",
         "request_not_found" to "That request no longer exists.",
         "track_not_found" to "That track no longer exists.",
+        "library_not_writable" to "The music library isn't writable by the server.",
+        "file_delete_failed" to "The file couldn't be deleted.",
         "album_not_found" to "That album no longer exists.",
         "artist_not_found" to "That artist no longer exists.",
         "playlist_not_found" to "That playlist no longer exists.",

android/app/src/main/java/com/fabledsword/minstrel/api/NetworkModule.kt

@@ -70,6 +70,9 @@ object NetworkModule {
             .addInterceptor(auth)
             .addInterceptor(baseUrl)
             .addInterceptor(logging)
+            // A network interceptor, so it sees the address the connection
+            // really reached and runs before any request byte is written.
+            .addNetworkInterceptor(CleartextGuardInterceptor())
             .connectTimeout(CONNECT_TIMEOUT_SECONDS, TimeUnit.SECONDS)
             .readTimeout(READ_TIMEOUT_SECONDS, TimeUnit.SECONDS)
             .build()

android/app/src/main/java/com/fabledsword/minstrel/api/endpoints/CastApi.kt

@@ -29,11 +29,20 @@ interface CastApi {
  * Request body. [expSeconds] is clamped server-side to [60, 86400];
  * the 21_600 default (6h) is long enough to play through any typical
  * track without re-minting mid-playback.
+ *
+ * [level] asks for the leveled stream (M464 #5001): the track rendered at
+ * the user's loudness gain, which the server works out from their setting.
+ * [asAlbum] says the track plays among its album in order, which picks
+ * album gain in auto mode. [prerender] says the speaker will fetch it
+ * soon, so the server renders it ahead.
  */
 @Serializable
 data class StreamTokenRequest(
     val trackId: String,
     val expSeconds: Int = 21_600,
+    val level: Boolean = false,
+    val asAlbum: Boolean = false,
+    val prerender: Boolean = false,
 )
 
 /**
@@ -53,4 +62,6 @@ data class StreamTokenResponse(
     val url: String,
     val mime: String = "audio/mpeg",
     val title: String = "",
+    /** [url] is the leveled stream; false when leveling is off or changes nothing. */
+    val leveled: Boolean = false,
 )

android/app/src/main/java/com/fabledsword/minstrel/api/endpoints/MeApi.kt

@@ -3,6 +3,7 @@ package com.fabledsword.minstrel.api.endpoints
 import com.fabledsword.minstrel.models.wire.ListenBrainzStatusWire
 import com.fabledsword.minstrel.models.wire.MyProfileWire
 import com.fabledsword.minstrel.models.wire.SystemPlaylistsStatusWire
+import com.fabledsword.minstrel.settings.data.NormalizationPrefs
 import kotlinx.serialization.SerialName
 import kotlinx.serialization.Serializable
 import retrofit2.http.Body
@@ -59,6 +60,14 @@ interface MeApi {
      */
     @PUT("api/me/listenbrainz")
     suspend fun setListenBrainz(@Body body: ListenBrainzPutBody): ListenBrainzStatusWire
+
+    /** The caller's loudness-normalization preference, or the defaults if never set. */
+    @GET("api/me/normalization")
+    suspend fun getNormalization(): NormalizationPrefs
+
+    /** Replaces the whole preference; returns what the server stored. */
+    @PUT("api/me/normalization")
+    suspend fun putNormalization(@Body body: NormalizationPrefs): NormalizationPrefs
 }
 
 /**

android/app/src/main/java/com/fabledsword/minstrel/api/endpoints/ReplayGainApi.kt

@@ -0,0 +1,15 @@
+package com.fabledsword.minstrel.api.endpoints
+
+import com.fabledsword.minstrel.models.wire.ReplayGainResponseWire
+import retrofit2.http.GET
+import retrofit2.http.Query
+
+/** The player's loudness lookup (#4997), kept apart from the browse surface in [LibraryApi]. */
+interface ReplayGainApi {
+    /**
+     * ReplayGain values for up to 200 comma-separated track ids. An id
+     * missing from `items` has not been measured yet.
+     */
+    @GET("api/tracks/replay-gain")
+    suspend fun getReplayGain(@Query("ids") ids: String): ReplayGainResponseWire
+}

android/app/src/main/java/com/fabledsword/minstrel/auth/AuthStore.kt

@@ -4,12 +4,19 @@ import com.fabledsword.minstrel.cache.audiocache.CacheSettings
 import com.fabledsword.minstrel.cache.db.dao.AuthSessionDao
 import com.fabledsword.minstrel.cache.db.entities.AuthSessionEntity
 import com.fabledsword.minstrel.di.ApplicationScope
+import com.fabledsword.minstrel.settings.data.NormalizationPrefs
 import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Deferred
+import kotlinx.coroutines.async
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.asStateFlow
 import kotlinx.coroutines.launch
+import kotlinx.coroutines.sync.Mutex
+import kotlinx.coroutines.sync.withLock
+import kotlinx.coroutines.withTimeoutOrNull
 import kotlinx.serialization.json.Json
+import timber.log.Timber
 import javax.inject.Inject
 import javax.inject.Singleton
 
@@ -27,6 +34,14 @@ import javax.inject.Singleton
  * in-memory state changes synchronously so the next interceptor read
  * sees the new value immediately; the DAO write coroutine catches up
  * shortly after.
+ *
+ * **The session cookie is the exception** (M462 #4985): it is persisted
+ * through [SessionVault] (Keystore-encrypted), not the Room row. On the
+ * first launch after the upgrade, a cookie still in the row is moved into
+ * the vault and the column cleared, so nobody is signed out by the change.
+ * If the Keystore cannot be used on a device, the cookie stays in the row
+ * as before rather than being lost. [awaitSessionHydrated] lets a caller
+ * that needs a definitive answer (the auth gate) wait for this.
  */
 // AuthStore is the single-row facade over auth_session (de-facto
 // app_preferences — see entity comment). It legitimately owns one
@@ -39,6 +54,7 @@ import javax.inject.Singleton
 @Singleton
 class AuthStore @Inject constructor(
     private val dao: AuthSessionDao,
+    private val vault: SessionVault,
     @ApplicationScope private val scope: CoroutineScope,
 ) {
     private val sessionCookieState = MutableStateFlow<String?>(null)
@@ -62,18 +78,32 @@ class AuthStore @Inject constructor(
     private val diagnosticsOptOutState = MutableStateFlow(false)
     val diagnosticsOptOut: StateFlow<Boolean> = diagnosticsOptOutState.asStateFlow()
 
+    private val normalizationState = MutableStateFlow(NormalizationPrefs.DEFAULT)
+    val normalization: StateFlow<NormalizationPrefs> = normalizationState.asStateFlow()
+
     private val json = Json { ignoreUnknownKeys = true }
 
+    // Serialises every cookie persist with the one-time hydration, so a
+    // sign-in or a 401 that lands while hydration runs is never overwritten
+    // by the stale value hydration read.
+    private val cookieLock = Mutex()
+
+    // Set by setSessionCookie. Once something has written the cookie this
+    // process, that value wins over whatever hydration finds on disk.
+    @Volatile private var cookieTouched = false
+
+    private val cookieHydration: Deferred<Unit> = scope.async { hydrateSessionCookie() }
+
     init {
         scope.launch {
             dao.observe().collect { row ->
-                sessionCookieState.value = row?.sessionCookie
                 baseUrlState.value = row?.baseUrl ?: DEFAULT_BASE_URL
                 userJsonState.value = row?.userJson
                 themeModeState.value = row?.themeMode
                 clientIdState.value = row?.clientId
                 cacheSettingsState.value = decodeCacheSettings(row?.cacheSettingsJson)
                 diagnosticsOptOutState.value = row?.diagnosticsOptOut ?: false
+                normalizationState.value = decodeNormalization(row?.normalizationJson)
             }
         }
     }
@@ -85,9 +115,57 @@ class AuthStore @Inject constructor(
         }.getOrDefault(CacheSettings.DEFAULT)
     }
 
+    private fun decodeNormalization(raw: String?): NormalizationPrefs {
+        if (raw.isNullOrEmpty()) return NormalizationPrefs.DEFAULT
+        return runCatching {
+            json.decodeFromString(NormalizationPrefs.serializer(), raw)
+        }.getOrDefault(NormalizationPrefs.DEFAULT)
+    }
+
+    /**
+     * Suspends until the stored session cookie has been loaded into
+     * [sessionCookie], or [HYDRATION_DEADLINE_MS] passes (rule 156: a wedged
+     * Keystore must not leave the start screen spinning). Returns false on
+     * the deadline; the caller then decides from whatever has loaded, and a
+     * late hydration still lands in [sessionCookie].
+     */
+    suspend fun awaitSessionHydrated(): Boolean {
+        val done = withTimeoutOrNull(HYDRATION_DEADLINE_MS) { cookieHydration.await() } != null
+        if (!done) Timber.w("auth store: session hydration passed its deadline; deciding without it")
+        return done
+    }
+
     fun setSessionCookie(value: String?) {
+        cookieTouched = true
         sessionCookieState.value = value
-        scope.launch { persistCookie(value) }
+        scope.launch { cookieLock.withLock { storeCookie(value) } }
+    }
+
+    private suspend fun hydrateSessionCookie() = cookieLock.withLock {
+        val legacy = runCatching { dao.get()?.sessionCookie }.getOrNull()
+        if (cookieTouched) return@withLock
+        // A cookie in the row is the newer one when both exist: the row is
+        // only written when the vault failed, and an install upgrading from
+        // before the vault has nothing in the vault yet.
+        val cookie = legacy ?: vault.read()
+        // Best-effort: if moving it fails, the session still loads this time
+        // and the move is retried on the next launch. Hydration must never
+        // throw, or awaitSessionHydrated would leave the auth gate stuck.
+        if (legacy != null) {
+            runCatching { storeCookie(legacy) }
+                .onFailure { Timber.w(it, "auth store: could not move the session cookie into the vault") }
+        }
+        sessionCookieState.value = cookie
+    }
+
+    // Vault first; the Room row only when the Keystore is unusable, so a
+    // broken Keystore degrades to the old storage rather than a sign-out.
+    private suspend fun storeCookie(value: String?) {
+        if (vault.write(value)) {
+            if (dao.get()?.sessionCookie != null) dao.setSessionCookie(null)
+        } else {
+            persistLegacyCookie(value)
+        }
     }
 
     fun setBaseUrl(value: String) {
@@ -121,7 +199,13 @@ class AuthStore @Inject constructor(
         scope.launch { persistDiagnosticsOptOut(value) }
     }
 
-    private suspend fun persistCookie(value: String?) {
+    fun setNormalization(value: NormalizationPrefs) {
+        normalizationState.value = value
+        val encoded = json.encodeToString(NormalizationPrefs.serializer(), value)
+        scope.launch { persistNormalization(encoded) }
+    }
+
+    private suspend fun persistLegacyCookie(value: String?) {
         if (dao.get() == null) {
             dao.upsert(currentEntity().copy(sessionCookie = value))
         } else {
@@ -177,9 +261,19 @@ class AuthStore @Inject constructor(
         }
     }
 
+    private suspend fun persistNormalization(json: String) {
+        if (dao.get() == null) {
+            dao.upsert(currentEntity().copy(normalizationJson = json))
+        } else {
+            dao.setNormalizationJson(json)
+        }
+    }
+
     private fun currentEntity(): AuthSessionEntity = AuthSessionEntity(
         id = ROW_ID,
-        sessionCookie = sessionCookieState.value,
+        // Never copied into the row: the cookie lives in the vault, and
+        // persistLegacyCookie sets it explicitly on the fallback path.
+        sessionCookie = null,
         baseUrl = baseUrlState.value,
         userJson = userJsonState.value,
         themeMode = themeModeState.value,
@@ -189,10 +283,18 @@ class AuthStore @Inject constructor(
             cacheSettingsState.value,
         ),
         diagnosticsOptOut = diagnosticsOptOutState.value,
+        normalizationJson = json.encodeToString(
+            NormalizationPrefs.serializer(),
+            normalizationState.value,
+        ),
     )
 
     companion object {
         const val DEFAULT_BASE_URL: String = "http://localhost:8080"
+
+        // Generous on purpose: hydration is one local row read and one
+        // Keystore decrypt, normally milliseconds. This only bounds "never".
+        const val HYDRATION_DEADLINE_MS: Long = 10_000
         private const val ROW_ID = 0
     }
 }

android/app/src/main/java/com/fabledsword/minstrel/auth/SessionVault.kt

@@ -0,0 +1,147 @@
+package com.fabledsword.minstrel.auth
+
+import android.content.Context
+import android.security.keystore.KeyGenParameterSpec
+import android.security.keystore.KeyProperties
+import dagger.Binds
+import dagger.Module
+import dagger.hilt.InstallIn
+import dagger.hilt.android.qualifiers.ApplicationContext
+import dagger.hilt.components.SingletonComponent
+import timber.log.Timber
+import java.security.KeyStore
+import java.util.Base64
+import javax.crypto.Cipher
+import javax.crypto.KeyGenerator
+import javax.crypto.SecretKey
+import javax.crypto.spec.GCMParameterSpec
+import javax.inject.Inject
+import javax.inject.Singleton
+
+/**
+ * Where the session cookie lives at rest (M462 #4985).
+ *
+ * The cookie is a bearer credential: anyone holding it is signed in as the
+ * user until the server expires or revokes it. It used to sit in plain text
+ * in the Room `auth_session` row, readable from any copy of the app's data
+ * directory (a rooted device, an adb backup of a debuggable build, a
+ * forensic image). Now only ciphertext is stored, under an AES key that
+ * lives in the Android Keystore and never leaves it, so a copy of the
+ * files alone yields nothing usable.
+ */
+interface SessionVault {
+    /** The stored cookie, or null when none is stored or it can't be decrypted. */
+    fun read(): String?
+
+    /**
+     * Stores [value], or clears the stored cookie when null. Returns false
+     * when the Keystore could not be used, so the caller can fall back
+     * rather than lose the session.
+     */
+    fun write(value: String?): Boolean
+}
+
+/**
+ * AES-GCM sealing of a short string, framed as base64(iv || ciphertext+tag).
+ * Kept apart from the Keystore so the framing can be unit-tested on the JVM
+ * with an ordinary key; the Android Keystore has no JVM implementation.
+ */
+internal object SealedBox {
+    private const val TRANSFORMATION = "AES/GCM/NoPadding"
+    private const val TAG_BITS = 128
+    private const val IV_BYTES = 12
+
+    // Binds a sealed value to its purpose: a blob sealed for something else
+    // under the same key will not open as a session cookie.
+    private val AAD = "minstrel-session-cookie-v1".toByteArray(Charsets.UTF_8)
+
+    fun seal(key: SecretKey, plaintext: String): String {
+        val cipher = Cipher.getInstance(TRANSFORMATION)
+        // No IV passed: the provider generates a fresh random one. Keystore
+        // keys refuse a caller-chosen IV for encryption by default.
+        cipher.init(Cipher.ENCRYPT_MODE, key)
+        cipher.updateAAD(AAD)
+        val sealed = cipher.iv + cipher.doFinal(plaintext.toByteArray(Charsets.UTF_8))
+        return Base64.getEncoder().encodeToString(sealed)
+    }
+
+    fun open(key: SecretKey, sealed: String): String {
+        val bytes = Base64.getDecoder().decode(sealed)
+        require(bytes.size > IV_BYTES) { "sealed value too short" }
+        val cipher = Cipher.getInstance(TRANSFORMATION)
+        cipher.init(Cipher.DECRYPT_MODE, key, GCMParameterSpec(TAG_BITS, bytes, 0, IV_BYTES))
+        cipher.updateAAD(AAD)
+        return String(cipher.doFinal(bytes, IV_BYTES, bytes.size - IV_BYTES), Charsets.UTF_8)
+    }
+}
+
+/**
+ * [SessionVault] backed by a Keystore AES key and a private prefs file that
+ * holds only the sealed value.
+ *
+ * A value that will not open (the key was wiped by a factory-reset of the
+ * Keystore, or the file was restored onto another device; app backup is off,
+ * but a vendor transfer tool may still copy files) is discarded and reported
+ * as absent. The user signs in again, which is the right outcome for a
+ * credential that no longer verifies.
+ */
+@Singleton
+class KeystoreSessionVault @Inject constructor(
+    @ApplicationContext context: Context,
+) : SessionVault {
+    private val prefs = context.getSharedPreferences(PREFS_NAME, Context.MODE_PRIVATE)
+
+    override fun read(): String? {
+        val sealed = prefs.getString(KEY_COOKIE, null) ?: return null
+        return runCatching { SealedBox.open(key(), sealed) }
+            .onFailure {
+                Timber.w(it, "session vault: stored cookie would not decrypt; discarding it")
+                prefs.edit().remove(KEY_COOKIE).commit()
+            }
+            .getOrNull()
+    }
+
+    override fun write(value: String?): Boolean = runCatching {
+        val editor = prefs.edit()
+        if (value == null) {
+            editor.remove(KEY_COOKIE)
+        } else {
+            editor.putString(KEY_COOKIE, SealedBox.seal(key(), value))
+        }
+        editor.commit()
+    }.onFailure {
+        Timber.w(it, "session vault: Keystore unavailable; cookie not stored in the vault")
+    }.getOrDefault(false)
+
+    private fun key(): SecretKey {
+        val keyStore = KeyStore.getInstance(ANDROID_KEYSTORE).apply { load(null) }
+        (keyStore.getKey(KEY_ALIAS, null) as? SecretKey)?.let { return it }
+        val generator = KeyGenerator.getInstance(KeyProperties.KEY_ALGORITHM_AES, ANDROID_KEYSTORE)
+        generator.init(
+            KeyGenParameterSpec.Builder(
+                KEY_ALIAS,
+                KeyProperties.PURPOSE_ENCRYPT or KeyProperties.PURPOSE_DECRYPT,
+            )
+                .setBlockModes(KeyProperties.BLOCK_MODE_GCM)
+                .setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_NONE)
+                .setKeySize(KEY_BITS)
+                .build(),
+        )
+        return generator.generateKey()
+    }
+
+    private companion object {
+        const val ANDROID_KEYSTORE = "AndroidKeyStore"
+        const val KEY_ALIAS = "minstrel_session_cookie"
+        const val KEY_BITS = 256
+        const val PREFS_NAME = "session_vault"
+        const val KEY_COOKIE = "sealed_cookie"
+    }
+}
+
+@Module
+@InstallIn(SingletonComponent::class)
+abstract class SessionVaultModule {
+    @Binds
+    abstract fun bindSessionVault(impl: KeystoreSessionVault): SessionVault
+}

android/app/src/main/java/com/fabledsword/minstrel/auth/ui/AuthGateViewModel.kt

@@ -16,10 +16,11 @@ import javax.inject.Inject
 
 /**
  * Computes the initial startDestination for the root NavHost based on
- * persisted auth state. Sits on top of AuthSessionDao directly rather
- * than AuthStore's StateFlow because the StateFlow defaults to null
- * until Room's first async emission — we need a definitive answer
- * before drawing any nav graph.
+ * persisted auth state. Reads the row from AuthSessionDao directly, and
+ * the session cookie only after [AuthStore.awaitSessionHydrated]: both
+ * StateFlows default to null until their async load lands, and we need a
+ * definitive answer before drawing any nav graph. The cookie is no longer
+ * in the row (it lives in the Keystore-backed SessionVault, #4985).
  *
  *   - no row at all          → ServerUrl   (first launch)
  *   - row with baseUrl, no cookie → Login   (URL configured, not yet signed in)
@@ -31,6 +32,7 @@ import javax.inject.Inject
 @HiltViewModel
 class AuthGateViewModel @Inject constructor(
     private val dao: AuthSessionDao,
+    private val authStore: AuthStore,
 ) : ViewModel() {
 
     private val internal = MutableStateFlow<Any?>(null)
@@ -38,12 +40,13 @@ class AuthGateViewModel @Inject constructor(
 
     init {
         viewModelScope.launch {
+            authStore.awaitSessionHydrated()
+            val signedIn = !authStore.sessionCookie.value.isNullOrEmpty()
             val row = dao.get()
             internal.value = when {
                 row == null -> ServerUrl
-                row.baseUrl == AuthStore.DEFAULT_BASE_URL && row.sessionCookie.isNullOrEmpty() ->
-                    ServerUrl
-                row.sessionCookie.isNullOrEmpty() -> Login
+                row.baseUrl == AuthStore.DEFAULT_BASE_URL && !signedIn -> ServerUrl
+                !signedIn -> Login
                 else -> Home
             }
         }

android/app/src/main/java/com/fabledsword/minstrel/cache/db/AppDatabase.kt

@@ -3,6 +3,8 @@ package com.fabledsword.minstrel.cache.db
 import androidx.room.Database
 import androidx.room.RoomDatabase
 import androidx.room.TypeConverters
+import androidx.room.migration.Migration
+import androidx.sqlite.db.SupportSQLiteDatabase
 import com.fabledsword.minstrel.cache.db.dao.AudioCacheIndexDao
 import com.fabledsword.minstrel.cache.db.dao.AuthSessionDao
 import com.fabledsword.minstrel.cache.db.dao.CachedAlbumDao
@@ -65,13 +67,22 @@ import com.fabledsword.minstrel.cache.db.entities.SyncMetadataEntity
         AuthSessionEntity::class,
         DiagnosticEventEntity::class,
     ],
+    // v10: + cached_tracks.trackGain/trackPeak and cached_albums.albumGain/
+    // albumPeak, the ReplayGain values the player levels by (M464 #5000).
+    // MIGRATION_9_10 also rewinds the sync cursor, so the next sync re-sends
+    // every row and an existing cache gains its values.
+    // v9: + auth_session.normalizationJson, the loudness-normalization
+    // preference (M464 #4998). The first schema step with an explicit
+    // Migration (MIGRATION_8_9): a destructive rebuild would also wipe this
+    // row — the server address and theme — and the queued offline writes,
+    // which is too much to lose for one added column.
     // v8: + cached_tracks.missing, the server's missing-file mark (#2704),
     // so cache-first surfaces stop offering files that cannot stream.
     // v7: + diagnostic_events table (M9) and the diagnosticsOptOut column
     // on auth_session. Pre-v1 destructive fallback rebuilds on mismatch —
     // which is exactly right here: the next sync refills every row with the
     // new column populated, so there is nothing to migrate by hand.
-    version = 8,
+    version = 10,
     exportSchema = true,
 )
 @TypeConverters(MinstrelTypeConverters::class)
@@ -92,3 +103,25 @@ abstract class AppDatabase : RoomDatabase() {
     abstract fun authSessionDao(): AuthSessionDao
     abstract fun diagnosticEventDao(): DiagnosticEventDao
 }
+
+/** v8 → v9: add the nullable normalization preference column (#4998). */
+val MIGRATION_8_9: Migration = object : Migration(8, 9) {
+    override fun migrate(db: SupportSQLiteDatabase) {
+        db.execSQL("ALTER TABLE auth_session ADD COLUMN normalizationJson TEXT")
+    }
+}
+
+/**
+ * v9 → v10: the gain columns (#5000). Rows synced before this carry no gains,
+ * and the sync is incremental, so it would never re-send them: the cursor goes
+ * back to 0 and the next sync is a full one, upserting every row in place.
+ */
+val MIGRATION_9_10: Migration = object : Migration(9, 10) {
+    override fun migrate(db: SupportSQLiteDatabase) {
+        db.execSQL("ALTER TABLE cached_tracks ADD COLUMN trackGain REAL")
+        db.execSQL("ALTER TABLE cached_tracks ADD COLUMN trackPeak REAL")
+        db.execSQL("ALTER TABLE cached_albums ADD COLUMN albumGain REAL")
+        db.execSQL("ALTER TABLE cached_albums ADD COLUMN albumPeak REAL")
+        db.execSQL("UPDATE sync_metadata SET cursor = 0")
+    }
+}

android/app/src/main/java/com/fabledsword/minstrel/cache/db/DatabaseModule.kt

@@ -37,6 +37,7 @@ object DatabaseModule {
             // launch, so users lose only the unsynced mutation queue
             // (acceptable while we're iterating). Replace with explicit
             // Migration entries before the first tagged release.
+            .addMigrations(MIGRATION_8_9, MIGRATION_9_10)
             .fallbackToDestructiveMigration(dropAllTables = true)
             .build()
 

android/app/src/main/java/com/fabledsword/minstrel/cache/db/dao/AuthSessionDao.kt

@@ -46,4 +46,8 @@ interface AuthSessionDao {
     /** Partial update: change only the per-device diagnostics opt-out. */
     @Query("UPDATE auth_session SET diagnosticsOptOut = :optOut WHERE id = 0")
     suspend fun setDiagnosticsOptOut(optOut: Boolean)
+
+    /** Partial update: change only the serialized normalization preference. */
+    @Query("UPDATE auth_session SET normalizationJson = :json WHERE id = 0")
+    suspend fun setNormalizationJson(json: String?)
 }

android/app/src/main/java/com/fabledsword/minstrel/cache/db/dao/CachedMutationDao.kt

@@ -31,4 +31,8 @@ interface CachedMutationDao {
 
     @Query("DELETE FROM cached_mutations")
     suspend fun clear()
+
+    /** Whether a write of [kind] is still waiting to be replayed. */
+    @Query("SELECT EXISTS(SELECT 1 FROM cached_mutations WHERE kind = :kind)")
+    suspend fun hasPending(kind: String): Boolean
 }

android/app/src/main/java/com/fabledsword/minstrel/cache/db/dao/CachedTrackDao.kt

@@ -38,6 +38,27 @@ interface CachedTrackDao {
     @Insert(onConflict = OnConflictStrategy.REPLACE)
     suspend fun upsertAll(rows: List<CachedTrackEntity>)
 
+    /**
+     * ReplayGain values for [ids] (M464 #5000): the track's own from its row,
+     * the album's from its album row. A track not in the cache has no row.
+     */
+    @Query(
+        "SELECT t.id AS id, t.trackGain AS trackGain, t.trackPeak AS trackPeak, " +
+            "a.albumGain AS albumGain, a.albumPeak AS albumPeak " +
+            "FROM cached_tracks t LEFT JOIN cached_albums a ON a.id = t.albumId " +
+            "WHERE t.id IN (:ids)",
+    )
+    suspend fun replayGains(ids: List<String>): List<CachedReplayGain>
+
     @Query("DELETE FROM cached_tracks WHERE id IN (:ids)")
     suspend fun deleteByIds(ids: List<String>)
 }
+
+/** One row of [CachedTrackDao.replayGains]. */
+data class CachedReplayGain(
+    val id: String,
+    val trackGain: Float?,
+    val trackPeak: Float?,
+    val albumGain: Float?,
+    val albumPeak: Float?,
+)

android/app/src/main/java/com/fabledsword/minstrel/cache/db/entities/AuthSessionEntity.kt

@@ -43,4 +43,10 @@ data class AuthSessionEntity(
      * choice lives here. Default false = honor the account flag.
      */
     val diagnosticsOptOut: Boolean = false,
+    /**
+     * JSON-encoded NormalizationPrefs (settings/data), the last value seen
+     * from the server or set here (M464 #4998). Null = never fetched; the
+     * defaults apply. Kept so offline playback still levels.
+     */
+    val normalizationJson: String? = null,
 )

android/app/src/main/java/com/fabledsword/minstrel/cache/db/entities/CachedAlbumEntity.kt

@@ -18,5 +18,8 @@ data class CachedAlbumEntity(
     val releaseDate: String? = null,
     val coverPath: String? = null,
     val mbid: String? = null,
+    // ReplayGain 2.0 album values (M464); null until every track is measured.
+    val albumGain: Float? = null,
+    val albumPeak: Float? = null,
     val fetchedAt: Instant = Clock.System.now(),
 )

android/app/src/main/java/com/fabledsword/minstrel/cache/db/entities/CachedTrackEntity.kt

@@ -26,5 +26,9 @@ data class CachedTrackEntity(
     val fileFormat: String? = null,
     val genre: String? = null,
     val missing: Boolean = false,
+    // ReplayGain 2.0 track values (M464), kept so cached audio levels
+    // offline. Null until the server has measured the track.
+    val trackGain: Float? = null,
+    val trackPeak: Float? = null,
     val fetchedAt: Instant = Clock.System.now(),
 )

android/app/src/main/java/com/fabledsword/minstrel/cache/mutations/MutationQueue.kt

@@ -2,6 +2,7 @@ package com.fabledsword.minstrel.cache.mutations
 
 import com.fabledsword.minstrel.cache.db.dao.CachedMutationDao
 import com.fabledsword.minstrel.cache.db.entities.CachedMutationEntity
+import com.fabledsword.minstrel.settings.data.NormalizationPrefs
 import kotlinx.coroutines.channels.BufferOverflow
 import kotlinx.coroutines.flow.MutableSharedFlow
 import kotlinx.coroutines.flow.SharedFlow
@@ -41,6 +42,11 @@ object MutationKind {
     // an undo collapses to the latest intent instead of replaying as two
     // opposed calls whose order decides the outcome.
     const val SUGGESTION_SNOOZE_TOGGLE: String = "suggestion_snooze_toggle"
+
+    // M464 #4998 loudness-normalization preference. The payload is the whole
+    // preference, a target state like the toggles above, so queued changes
+    // collapse to the last one and an older one can never be replayed last.
+    const val NORMALIZATION_SET: String = "normalization_set"
 }
 
 /**
@@ -85,6 +91,7 @@ data class RequestCreatePayload(
  * This matches `feedback_offline_first_for_server_writes` — writes
  * never go fire-and-forget.
  */
+@Suppress("TooManyFunctions") // one enqueue per mutation kind, like the replayer's dispatchers
 @Singleton
 class MutationQueue @Inject constructor(
     private val dao: CachedMutationDao,
@@ -177,6 +184,12 @@ class MutationQueue @Inject constructor(
         ),
     )
 
+    /** Queues the user's whole normalization preference for replay. */
+    suspend fun enqueueNormalizationSet(prefs: NormalizationPrefs): Long = insertUserDriven(
+        MutationKind.NORMALIZATION_SET,
+        json.encodeToString(NormalizationPrefs.serializer(), prefs),
+    )
+
     suspend fun enqueueRequestCancel(requestId: String): Long = insertUserDriven(
         MutationKind.REQUEST_CANCEL,
         json.encodeToString(

android/app/src/main/java/com/fabledsword/minstrel/cache/mutations/MutationReplayer.kt

@@ -7,6 +7,7 @@ import com.fabledsword.minstrel.api.endpoints.DiscoverApi
 import com.fabledsword.minstrel.api.endpoints.EventsApi
 import com.fabledsword.minstrel.api.endpoints.FlagRequest
 import com.fabledsword.minstrel.api.endpoints.LikesApi
+import com.fabledsword.minstrel.api.endpoints.MeApi
 import com.fabledsword.minstrel.api.endpoints.PlaybackErrorReportRequest
 import com.fabledsword.minstrel.api.endpoints.PlaybackErrorsApi
 import com.fabledsword.minstrel.api.endpoints.PlaylistsApi
@@ -22,6 +23,7 @@ import com.fabledsword.minstrel.cache.db.dao.CachedMutationDao
 import com.fabledsword.minstrel.cache.db.entities.CachedMutationEntity
 import com.fabledsword.minstrel.di.ApplicationScope
 import com.fabledsword.minstrel.likes.data.LikesRepository
+import com.fabledsword.minstrel.settings.data.NormalizationPrefs
 import com.fabledsword.minstrel.models.wire.CreateRequestBody
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.flow.distinctUntilChanged
@@ -79,6 +81,7 @@ class MutationReplayer @Inject constructor(
     private val eventsApi: EventsApi = retrofit.create()
     private val requestsApi: RequestsApi = retrofit.create()
     private val playbackErrorsApi: PlaybackErrorsApi = retrofit.create()
+    private val meApi: MeApi = retrofit.create()
 
     private val mutex = Mutex()
 
@@ -166,6 +169,7 @@ class MutationReplayer @Inject constructor(
         MutationKind.REQUEST_CANCEL -> dispatchRequestCancel(row.payload)
         MutationKind.PLAYBACK_ERROR_REPORT -> dispatchPlaybackErrorReport(row.payload)
         MutationKind.SUGGESTION_SNOOZE_TOGGLE -> dispatchSuggestionSnoozeToggle(row.payload)
+        MutationKind.NORMALIZATION_SET -> dispatchNormalizationSet(row.payload)
         // Unknown kind — drop so a stale schema entry can't wedge the queue.
         else -> Outcome.DROP
     }
@@ -279,6 +283,16 @@ class MutationReplayer @Inject constructor(
         return Outcome.SENT
     }
 
+    /**
+     * Sends the queued normalization preference. The device already shows
+     * it, so the server's echo is not written back: a change made since the
+     * row was queued would be a newer row, and the collapse keeps only that.
+     */
+    private suspend fun dispatchNormalizationSet(payload: String): Outcome {
+        meApi.putNormalization(json.decodeFromString(NormalizationPrefs.serializer(), payload))
+        return Outcome.SENT
+    }
+
     private suspend fun dispatchPlaybackErrorReport(payload: String): Outcome {
         val decoded = json.decodeFromString(PlaybackErrorReportPayload.serializer(), payload)
         playbackErrorsApi.report(
@@ -303,7 +317,8 @@ class MutationReplayer @Inject constructor(
 /**
  * Row ids of desired-state toggles superseded by a later toggle for the same
  * entity. Applies to every kind whose payload encodes a TARGET state rather
- * than an action — like-toggles and suggestion snoozes (#2374) — because
+ * than an action — like-toggles, suggestion snoozes (#2374) and the
+ * normalization preference (#4998) — because
  * replaying a stale one last would invert the final state.
  *
  * Top-level and pure so it can be unit-tested without standing up a Retrofit
@@ -340,5 +355,10 @@ private fun toggleKeyOf(row: CachedMutationEntity, json: Json): String? = when (
         json.decodeFromString(SuggestionSnoozeTogglePayload.serializer(), row.payload)
     }.getOrNull()?.let { "${row.kind}:${it.mbid}" }
 
+    // One preference per user, so every normalization row shares one key.
+    MutationKind.NORMALIZATION_SET -> runCatching {
+        json.decodeFromString(NormalizationPrefs.serializer(), row.payload)
+    }.getOrNull()?.let { row.kind }
+
     else -> null
 }

android/app/src/main/java/com/fabledsword/minstrel/cache/sync/SyncController.kt

@@ -206,6 +206,8 @@ private fun SyncAlbumWire.toEntity(): CachedAlbumEntity = CachedAlbumEntity(
     releaseDate = releaseDate,
     coverPath = coverArtPath,
     mbid = mbid,
+    albumGain = albumGain,
+    albumPeak = albumPeak,
 )
 
 private fun SyncTrackWire.toEntity(): CachedTrackEntity = CachedTrackEntity(
@@ -220,4 +222,6 @@ private fun SyncTrackWire.toEntity(): CachedTrackEntity = CachedTrackEntity(
     fileFormat = fileFormat,
     genre = genre,
     missing = missing,
+    trackGain = trackGain,
+    trackPeak = trackPeak,
 )

android/app/src/main/java/com/fabledsword/minstrel/models/wire/ReplayGainWire.kt

@@ -0,0 +1,18 @@
+package com.fabledsword.minstrel.models.wire
+
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+
+/** One track's entry in `GET /api/tracks/replay-gain` (#4997). Decode-only. */
+@Serializable
+data class ReplayGainWire(
+    @SerialName("track_gain") val trackGain: Float? = null,
+    @SerialName("track_peak") val trackPeak: Float? = null,
+    @SerialName("album_gain") val albumGain: Float? = null,
+    @SerialName("album_peak") val albumPeak: Float? = null,
+)
+
+@Serializable
+data class ReplayGainResponseWire(
+    val items: Map<String, ReplayGainWire> = emptyMap(),
+)

android/app/src/main/java/com/fabledsword/minstrel/models/wire/SyncResponseWire.kt

@@ -28,6 +28,10 @@ data class SyncAlbumWire(
     @SerialName("release_date") val releaseDate: String? = null,
     @SerialName("cover_art_path") val coverArtPath: String? = null,
     val mbid: String? = null,
+    // The album's ReplayGain 2.0 values (#4997): dB to -18 LUFS and a linear
+    // peak. Null until every track on the album is measured.
+    @SerialName("album_gain") val albumGain: Float? = null,
+    @SerialName("album_peak") val albumPeak: Float? = null,
 )
 
 @Serializable
@@ -51,6 +55,9 @@ data class SyncTrackWire(
     // its tracks stay playable, which is the correct reading of "this server
     // has nothing to say about missing files".
     val missing: Boolean = false,
+    // The track's ReplayGain 2.0 values (#4997); null until it is measured.
+    @SerialName("track_gain") val trackGain: Float? = null,
+    @SerialName("track_peak") val trackPeak: Float? = null,
 )
 
 /**

android/app/src/main/java/com/fabledsword/minstrel/player/MinstrelForwardingPlayer.kt

@@ -93,6 +93,8 @@ class MinstrelForwardingPlayer(
          * one. Diagnostics-only; see [TransportObservation].
          */
         val onTransport: (TransportObservation) -> Unit = {},
+        /** The renderer's 1-based queue position, every poll. */
+        val onRendererTrack: (trackNumber: Int) -> Unit = {},
     )
 
     private val scope = CoroutineScope(SupervisorJob() + Dispatchers.IO)
@@ -622,6 +624,7 @@ class MinstrelForwardingPlayer(
             trackNumber = info.track,
         )
         syncLocalCursorToRemote(sonosTrack = info.track, trackUri = info.trackUri)
+        events.onRendererTrack(info.track)
         val transport = active.avTransport.getTransportInfo()
         when (transport.state) {
             TransportState.PLAYING -> {

android/app/src/main/java/com/fabledsword/minstrel/player/MinstrelPlayerService.kt

@@ -12,8 +12,10 @@ import androidx.media3.session.SessionCommand
 import com.fabledsword.minstrel.MainActivity
 import com.fabledsword.minstrel.likes.data.LikesRepository
 import com.fabledsword.minstrel.likes.data.LikesRepository.Companion.ENTITY_TRACK
+import com.fabledsword.minstrel.settings.data.NormalizationRepository
 import com.google.common.collect.ImmutableList
 import dagger.hilt.android.AndroidEntryPoint
+import kotlinx.coroutines.CancellationException
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.ExperimentalCoroutinesApi
@@ -25,6 +27,7 @@ import kotlinx.coroutines.flow.flatMapLatest
 import kotlinx.coroutines.flow.flowOf
 import kotlinx.coroutines.flow.onStart
 import kotlinx.coroutines.launch
+import timber.log.Timber
 import javax.inject.Inject
 
 /**
@@ -66,6 +69,8 @@ class MinstrelPlayerService : MediaSessionService() {
 
     @Inject lateinit var likesRepository: LikesRepository
 
+    @Inject lateinit var normalizationRepository: NormalizationRepository
+
     private val serviceScope = CoroutineScope(SupervisorJob() + Dispatchers.Main.immediate)
 
     private var mediaSession: MediaSession? = null
@@ -82,6 +87,21 @@ class MinstrelPlayerService : MediaSessionService() {
             .build()
         mediaSession = session
         serviceScope.launch { observeLikeState(session, player) }
+        serviceScope.launch { refreshNormalization() }
+    }
+
+    // Takes up a leveling preference changed on another device (M464 #5000).
+    // Offline, the device's copy stands, which is the one playback reads.
+    private suspend fun refreshNormalization() {
+        try {
+            normalizationRepository.refresh()
+        } catch (e: CancellationException) {
+            throw e
+        } catch (
+            @Suppress("TooGenericExceptionCaught") e: Throwable,
+        ) {
+            Timber.d(e, "normalization refresh skipped")
+        }
     }
 
     /**

android/app/src/main/java/com/fabledsword/minstrel/player/PlayerController.kt

@@ -14,6 +14,8 @@ import androidx.media3.session.MediaController
 import androidx.media3.session.SessionToken
 import com.fabledsword.minstrel.di.ApplicationScope
 import com.fabledsword.minstrel.models.TrackRef
+import com.fabledsword.minstrel.player.gain.GainAudioProcessor
+import com.fabledsword.minstrel.player.gain.ReplayGainStore
 import com.fabledsword.minstrel.playlists.data.PlaylistsRepository
 import com.fabledsword.minstrel.playlists.data.toPlayableTrackRefs
 import com.fabledsword.minstrel.shared.resolveServerUrl
@@ -69,6 +71,7 @@ class PlayerController @Inject constructor(
     private val playerFactory: PlayerFactory,
     private val activeUpnpHolder: com.fabledsword.minstrel.player.output.ActiveUpnpHolder,
     private val remoteState: RemotePlayerState,
+    private val replayGains: ReplayGainStore,
 ) {
 
     /**
@@ -277,6 +280,11 @@ class PlayerController @Inject constructor(
         queueRefs = playable.tracks
         val items = playable.tracks.map { it.toMediaItem(source) }
         val startIndex = playable.initialIndex
+        // Gains for the first tracks, so the first one levels from its first
+        // sample rather than ramping in once the lookup lands.
+        replayGains.request(
+            playable.tracks.drop(startIndex).take(GAIN_PREFETCH).map { it.id },
+        )
         // Drift #562 cold-boot resume calls this from a non-Main suspend
         // context after awaitReady() unblocks (ResumeController launches
         // on Dispatchers.Default by the time it reaches us). MediaController
@@ -792,7 +800,13 @@ class PlayerController @Inject constructor(
                 // scrubber a real total even when the wrapped ExoPlayer is
                 // paused under UPnP (it never probes a duration in that state).
                 if (durationSec > 0) setDurationMs(durationSec.toLong() * MS_PER_SECOND)
-                if (source != null) setExtras(sourceExtras(source))
+                // Album and track position let the gain processor tell an
+                // album played in order from a mix (M464 #5000).
+                trackNumber?.let { setTrackNumber(it) }
+                discNumber?.let { setDiscNumber(it) }
+                val extras = GainAudioProcessor.albumExtras(albumId)
+                if (source != null) extras.putAll(sourceExtras(source))
+                setExtras(extras)
                 // Point the notification / lock-screen art at the SAME album
                 // cover the in-app surfaces use (TrackRef.coverUrl ->
                 // /api/albums/{id}/cover). Without this, Media3 falls back to
@@ -860,6 +874,7 @@ class PlayerController @Inject constructor(
         const val MINSTREL_SOURCE_KEY: String = "minstrel_source"
         private const val MS_PER_SECOND = 1_000L
         private const val MAX_INTERPOLATION_DRIFT_MS = 5_000L
+        private const val GAIN_PREFETCH = 20
     }
 }
 

android/app/src/main/java/com/fabledsword/minstrel/player/PlayerFactory.kt

@@ -4,6 +4,7 @@ import android.content.Context
 import androidx.media3.common.AudioAttributes
 import androidx.media3.common.C
 import androidx.media3.common.Player
+import androidx.media3.common.audio.AudioProcessor
 import androidx.media3.common.util.BitmapLoader
 import androidx.media3.database.StandaloneDatabaseProvider
 import androidx.media3.datasource.DataSourceBitmapLoader
@@ -12,11 +13,18 @@ import androidx.media3.datasource.cache.CacheDataSource
 import androidx.media3.datasource.cache.LeastRecentlyUsedCacheEvictor
 import androidx.media3.datasource.cache.SimpleCache
 import androidx.media3.datasource.okhttp.OkHttpDataSource
+import androidx.media3.exoplayer.DefaultRenderersFactory
 import androidx.media3.exoplayer.ExoPlayer
+import androidx.media3.exoplayer.audio.AudioSink
+import androidx.media3.exoplayer.audio.DefaultAudioSink
 import androidx.media3.exoplayer.source.DefaultMediaSourceFactory
 import androidx.media3.session.CacheBitmapLoader
+import com.fabledsword.minstrel.auth.AuthStore
 import com.fabledsword.minstrel.cache.audiocache.CacheConfig
+import com.fabledsword.minstrel.player.gain.GainAudioProcessor
+import com.fabledsword.minstrel.player.gain.ReplayGainStore
 import com.fabledsword.minstrel.player.output.ActiveUpnpHolder
+import com.fabledsword.minstrel.player.output.SonosQueueLoader
 import dagger.hilt.android.qualifiers.ApplicationContext
 import kotlinx.coroutines.channels.BufferOverflow
 import kotlinx.coroutines.flow.MutableSharedFlow
@@ -56,6 +64,9 @@ class PlayerFactory @Inject constructor(
     private val activeUpnpHolder: ActiveUpnpHolder,
     private val remoteState: RemotePlayerState,
     private val serverHealth: com.fabledsword.minstrel.connectivity.NetworkStatusController,
+    private val authStore: AuthStore,
+    private val replayGains: ReplayGainStore,
+    private val sonosQueue: SonosQueueLoader,
 ) {
     private val cacheDir: File = File(context.cacheDir, "audio_cache").apply { mkdirs() }
 
@@ -120,6 +131,7 @@ class PlayerFactory @Inject constructor(
                 onStalled = { trackId -> stallEventsInternal.tryEmit(trackId) },
                 onQueueTruncated = { queueRepairInternal.tryEmit(Unit) },
                 onTransport = { transportInternal.tryEmit(it) },
+                onRendererTrack = { sonosQueue.onRendererTrack(it) },
             ),
         )
     }
@@ -142,7 +154,28 @@ class PlayerFactory @Inject constructor(
         val mediaSourceFactory = DefaultMediaSourceFactory(context)
             .setDataSourceFactory(cacheDataSource)
 
-        return ExoPlayer.Builder(context)
+        // Loudness normalization (M464 #5000) runs inside the audio sink so
+        // each track's gain starts on its first sample. Audio offload would
+        // bypass the sink's processors; ExoPlayer leaves it off unless asked
+        // (TrackSelectionParameters.audioOffloadPreferences), and nothing here
+        // asks, so leveling always applies.
+        val gainProcessor = GainAudioProcessor(
+            prefs = { authStore.normalization.value },
+            store = replayGains,
+        )
+        val renderersFactory = object : DefaultRenderersFactory(context) {
+            override fun buildAudioSink(
+                context: Context,
+                enableFloatOutput: Boolean,
+                enableAudioOutputPlaybackParams: Boolean,
+            ): AudioSink = DefaultAudioSink.Builder(context)
+                .setEnableFloatOutput(enableFloatOutput)
+                .setEnableAudioOutputPlaybackParameters(enableAudioOutputPlaybackParams)
+                .setAudioProcessors(arrayOf<AudioProcessor>(gainProcessor))
+                .build()
+        }
+
+        val exo = ExoPlayer.Builder(context, renderersFactory)
             .setMediaSourceFactory(mediaSourceFactory)
             .setAudioAttributes(
                 AudioAttributes.Builder()
@@ -153,6 +186,17 @@ class PlayerFactory @Inject constructor(
             )
             .setHandleAudioBecomingNoisy(true)
             .build()
+        // The processor finds a track's neighbours in play order, which
+        // depends on shuffle mode.
+        gainProcessor.shuffleEnabled = exo.shuffleModeEnabled
+        exo.addListener(
+            object : Player.Listener {
+                override fun onShuffleModeEnabledChanged(shuffleModeEnabled: Boolean) {
+                    gainProcessor.shuffleEnabled = shuffleModeEnabled
+                }
+            },
+        )
+        return exo
     }
 
     /**

android/app/src/main/java/com/fabledsword/minstrel/player/StreamTokenProvider.kt

@@ -19,6 +19,13 @@ import javax.inject.Singleton
 class StreamTokenProvider @Inject constructor(retrofit: Retrofit) {
     private val api: CastApi = retrofit.create()
 
-    suspend fun mint(trackId: String): StreamTokenResponse =
-        api.streamToken(StreamTokenRequest(trackId = trackId))
+    /**
+     * Mints a URL for a speaker, leveled when the user's setting calls for
+     * it (M464 #5002). The server answers with the plain stream when it does
+     * not, so every speaker URL asks.
+     */
+    suspend fun mint(trackId: String, asAlbum: Boolean = false, prerender: Boolean = false): StreamTokenResponse =
+        api.streamToken(
+            StreamTokenRequest(trackId = trackId, level = true, asAlbum = asAlbum, prerender = prerender),
+        )
 }

android/app/src/main/java/com/fabledsword/minstrel/player/gain/GainAudioProcessor.kt

@@ -0,0 +1,139 @@
+package com.fabledsword.minstrel.player.gain
+
+import android.os.Bundle
+import androidx.media3.common.C
+import androidx.media3.common.MediaItem
+import androidx.media3.common.Player
+import androidx.media3.common.Timeline
+import androidx.media3.common.audio.AudioProcessor
+import androidx.media3.common.audio.BaseAudioProcessor
+import com.fabledsword.minstrel.settings.data.NormalizationBoost
+import com.fabledsword.minstrel.settings.data.NormalizationMode
+import com.fabledsword.minstrel.settings.data.NormalizationPrefs
+import java.nio.ByteBuffer
+
+/**
+ * Applies each track's loudness gain inside ExoPlayer's audio sink (M464
+ * #5000), so the level changes on the exact sample a track starts, gapless
+ * transitions included. `Player.setVolume` could do neither: it stops at 1,
+ * and set from a transition callback it lands about two seconds late
+ * because the next track is already buffered (androidx/media#418).
+ *
+ * Media3 1.11 flushes the sink's processors at every item boundary with the
+ * playlist [Timeline] and the new item's period, which is how this knows
+ * which track it is processing and who its neighbours are.
+ *
+ * Boosts above unity are held under -1 dBFS by a peak limiter when the user
+ * chose one. In headroom mode the gain already stops short of the track's
+ * true peak, and the final clamp only guards against a bad measurement.
+ *
+ * Runs on the playback thread. [prefs] and [store] are read per buffer, so a
+ * changed preference or a gain that arrives mid-track applies at once,
+ * through a short ramp rather than a step.
+ */
+class GainAudioProcessor(
+    private val prefs: () -> NormalizationPrefs,
+    private val store: ReplayGainStore,
+) : BaseAudioProcessor() {
+
+    /** Mirrors the player's shuffle mode, so neighbours are found in play order. */
+    @Volatile var shuffleEnabled: Boolean = false
+
+    private var currentId: String? = null
+    private var asAlbum = false
+    private val stage = GainStage()
+
+    override fun onConfigure(inputAudioFormat: AudioProcessor.AudioFormat): AudioProcessor.AudioFormat =
+        when (inputAudioFormat.encoding) {
+            C.ENCODING_PCM_16BIT, C.ENCODING_PCM_FLOAT -> inputAudioFormat
+            else -> AudioProcessor.AudioFormat.NOT_SET
+        }
+
+    override fun onFlush(streamMetadata: AudioProcessor.StreamMetadata) {
+        identify(streamMetadata)
+        // A new stream starts at its own level: ramping in from the previous
+        // track's gain would swell or dip its first moments.
+        stage.reset(inputAudioFormat.sampleRate, inputAudioFormat.channelCount, targetGain())
+    }
+
+    override fun onReset() {
+        currentId = null
+        asAlbum = false
+    }
+
+    override fun queueInput(inputBuffer: ByteBuffer) {
+        val size = inputBuffer.remaining()
+        if (size == 0) return
+        val out = replaceOutputBuffer(size)
+        val p = prefs()
+        val target = targetGain(p)
+        val limiting = p.mode != NormalizationMode.OFF && p.boost == NormalizationBoost.LIMITER
+        if (stage.isUnity(target, limiting)) {
+            out.put(inputBuffer)
+        } else {
+            stage.process(
+                input = inputBuffer,
+                out = out,
+                channels = inputAudioFormat.channelCount,
+                isFloat = inputAudioFormat.encoding == C.ENCODING_PCM_FLOAT,
+                target = target,
+                limiting = limiting,
+            )
+        }
+        out.flip()
+    }
+
+    private fun targetGain(p: NormalizationPrefs = prefs()): Float {
+        val id = currentId ?: return 1f
+        return GainMath.dbToLinear(GainMath.gainDb(p, store.get(id), asAlbum))
+    }
+
+    // Which track this stream is, and whether it is playing as part of its
+    // album. Also asks the store for the gains of the tracks coming up, so
+    // each is known before it starts.
+    private fun identify(meta: AudioProcessor.StreamMetadata) {
+        currentId = null
+        asAlbum = false
+        val uid = meta.periodUid
+        if (uid == null || meta.timeline.isEmpty) return
+        val timeline = meta.timeline
+        val index = timeline.getPeriodByUid(uid, Timeline.Period()).windowIndex
+        val window = Timeline.Window()
+        fun itemAt(i: Int): MediaItem? =
+            if (i == C.INDEX_UNSET) null else timeline.getWindow(i, window).mediaItem
+        fun nextOf(i: Int) = timeline.getNextWindowIndex(i, Player.REPEAT_MODE_OFF, shuffleEnabled)
+
+        val cur = itemAt(index)
+        val prev = itemAt(timeline.getPreviousWindowIndex(index, Player.REPEAT_MODE_OFF, shuffleEnabled))
+        val next = itemAt(nextOf(index))
+        if (cur != null) {
+            currentId = cur.mediaId
+            asAlbum = GainMath.playingAsAlbum(prev?.albumPosition(), cur.albumPosition(), next?.albumPosition())
+        }
+
+        val upcoming = mutableListOf<String>()
+        var i = index
+        while (i != C.INDEX_UNSET && upcoming.size < LOOKAHEAD) {
+            itemAt(i)?.let { upcoming += it.mediaId }
+            i = nextOf(i)
+        }
+        store.request(upcoming)
+    }
+
+    companion object {
+        /** MediaMetadata extras key holding the track's album id. */
+        const val EXTRA_ALBUM_ID = "minstrel.album_id"
+
+        private const val LOOKAHEAD = 20
+
+        /** Puts what [albumPosition] reads into a MediaItem's metadata extras. */
+        fun albumExtras(albumId: String, into: Bundle = Bundle()): Bundle =
+            into.apply { putString(EXTRA_ALBUM_ID, albumId) }
+    }
+}
+
+private fun MediaItem.albumPosition(): AlbumPosition = AlbumPosition(
+    albumId = mediaMetadata.extras?.getString(GainAudioProcessor.EXTRA_ALBUM_ID),
+    discNumber = mediaMetadata.discNumber,
+    trackNumber = mediaMetadata.trackNumber,
+)

android/app/src/main/java/com/fabledsword/minstrel/player/gain/GainMath.kt

@@ -0,0 +1,96 @@
+package com.fabledsword.minstrel.player.gain
+
+import com.fabledsword.minstrel.settings.data.NormalizationBoost
+import com.fabledsword.minstrel.settings.data.NormalizationMode
+import com.fabledsword.minstrel.settings.data.NormalizationPrefs
+import kotlin.math.log10
+import kotlin.math.min
+import kotlin.math.pow
+
+/**
+ * One track's ReplayGain 2.0 values from the server (#4997): dB to the
+ * -18 LUFS reference, and linear true peaks. A null field has not been
+ * measured yet.
+ */
+data class ReplayGain(
+    val trackGain: Float?,
+    val trackPeak: Float?,
+    val albumGain: Float?,
+    val albumPeak: Float?,
+) {
+    companion object {
+        val NONE = ReplayGain(null, null, null, null)
+    }
+}
+
+/** Where a queue item sits in its album, for the auto-mode album rule. */
+data class AlbumPosition(val albumId: String?, val discNumber: Int?, val trackNumber: Int?)
+
+/**
+ * Loudness-normalization math (M464 #5000). The same rules as the web
+ * player's `web/src/lib/player/gain.ts`, so a track levels the same on
+ * every device.
+ */
+object GainMath {
+    private const val REFERENCE_LUFS = -18
+
+    /** Headroom mode raises a quiet track only until its true peak reaches this. */
+    const val PEAK_CEILING_DBTP = -1f
+
+    /**
+     * No track is raised more than this, whatever its measurement says: a
+     * near-silent track would otherwise come out as amplified noise.
+     */
+    const val MAX_BOOST_DB = 12f
+
+    private const val DISC_STRIDE = 1000
+
+    // Amplitude decibels: 20 dB per factor of ten.
+    private const val DB_PER_DECADE = 20f
+
+    /**
+     * The gain to apply, in dB. 0 when leveling is off or the track has not
+     * been measured: an unmeasured track plays as mastered.
+     */
+    fun gainDb(prefs: NormalizationPrefs, g: ReplayGain?, asAlbum: Boolean): Float {
+        if (prefs.mode == NormalizationMode.OFF || g == null) return 0f
+        val wantAlbum = prefs.mode == NormalizationMode.ALBUM ||
+            (prefs.mode == NormalizationMode.AUTO && asAlbum)
+        // Album gain falls back to track gain while the album is still being
+        // measured; track gain never falls back to album gain.
+        val useAlbum = wantAlbum && g.albumGain != null
+        val gain = if (useAlbum) g.albumGain else g.trackGain
+        val peak = if (useAlbum) g.albumPeak else g.trackPeak
+        return gain?.let { leveled(prefs, it, peak) } ?: 0f
+    }
+
+    private fun leveled(prefs: NormalizationPrefs, gain: Float, peak: Float?): Float {
+        var db = gain + (prefs.targetLufs - REFERENCE_LUFS)
+        if (prefs.boost == NormalizationBoost.HEADROOM && peak != null && peak > 0f) {
+            db = min(db, PEAK_CEILING_DBTP - DB_PER_DECADE * log10(peak))
+        }
+        return min(db, MAX_BOOST_DB)
+    }
+
+    /**
+     * Whether the current item is being played as part of its album, in
+     * order: a neighbour in play order is from the same album and sits on
+     * the right side of it. That is when album gain keeps the album's own
+     * dynamics (a quiet intro stays quiet); anywhere else track gain levels
+     * the mix.
+     */
+    fun playingAsAlbum(prev: AlbumPosition?, cur: AlbumPosition, next: AlbumPosition?): Boolean {
+        val curOrder = order(cur)
+        if (cur.albumId == null || curOrder == null) return false
+        val prevOrder = prev?.takeIf { it.albumId == cur.albumId }?.let { order(it) }
+        val nextOrder = next?.takeIf { it.albumId == cur.albumId }?.let { order(it) }
+        return (prevOrder != null && prevOrder < curOrder) || (nextOrder != null && nextOrder > curOrder)
+    }
+
+    // Disc-major track order. A track with no number has no place in the
+    // order and is never evidence of album play.
+    private fun order(p: AlbumPosition): Int? =
+        p.trackNumber?.let { (p.discNumber ?: 1) * DISC_STRIDE + it }
+
+    fun dbToLinear(db: Float): Float = 10f.pow(db / DB_PER_DECADE)
+}

android/app/src/main/java/com/fabledsword/minstrel/player/gain/GainStage.kt

@@ -0,0 +1,82 @@
+package com.fabledsword.minstrel.player.gain
+
+import java.nio.ByteBuffer
+import kotlin.math.abs
+import kotlin.math.exp
+import kotlin.math.max
+import kotlin.math.roundToInt
+
+/**
+ * The sample arithmetic of [GainAudioProcessor], apart from Media3 so it can
+ * be tested on the JVM: a gain that ramps toward its target, then an
+ * optional peak limiter, then a clamp to full scale. Interleaved 16-bit or
+ * float PCM in, the same format out.
+ */
+internal class GainStage {
+    private var gain = 1f
+    private var envelope = 0f
+    private var rampCoeff = 1f
+    private var releaseCoeff = 0f
+    private var frame = FloatArray(2)
+
+    /** Sets the sample rate and channel count, and starts the gain at [startGain]. */
+    fun reset(sampleRate: Int, channels: Int, startGain: Float) {
+        val rate = sampleRate.coerceAtLeast(1).toFloat()
+        rampCoeff = 1f - exp(-1f / (RAMP_SECONDS * rate))
+        releaseCoeff = exp(-1f / (RELEASE_SECONDS * rate))
+        if (frame.size < channels) frame = FloatArray(channels)
+        gain = startGain
+        envelope = 0f
+    }
+
+    /** True when processing would copy the input unchanged. */
+    fun isUnity(target: Float, limiting: Boolean): Boolean = gain == 1f && target == 1f && !limiting
+
+    /**
+     * Processes every whole frame of [input] into [out]. A trailing partial
+     * frame is dropped, as Media3's own processors do.
+     */
+    @Suppress("LongParameterList") // the PCM layout is four facts; a holder type would only rename them
+    fun process(
+        input: ByteBuffer,
+        out: ByteBuffer,
+        channels: Int,
+        isFloat: Boolean,
+        target: Float,
+        limiting: Boolean,
+    ) {
+        val bytesPerFrame = channels * if (isFloat) FLOAT_BYTES else PCM16_BYTES
+        val frames = input.remaining() / bytesPerFrame
+        repeat(frames) {
+            gain += (target - gain) * rampCoeff
+            var peak = 0f
+            for (c in 0 until channels) {
+                val s = (if (isFloat) input.float else input.short / PCM16_SCALE) * gain
+                frame[c] = s
+                peak = max(peak, abs(s))
+            }
+            var reduce = 1f
+            if (limiting) {
+                envelope = max(peak, envelope * releaseCoeff)
+                if (envelope > LIMIT_CEILING) reduce = LIMIT_CEILING / envelope
+            }
+            for (c in 0 until channels) {
+                val v = (frame[c] * reduce).coerceIn(-1f, 1f)
+                if (isFloat) out.putFloat(v) else out.putShort((v * PCM16_MAX).roundToInt().toShort())
+            }
+        }
+        input.position(input.limit())
+    }
+
+    companion object {
+        /** -1 dBFS, the ceiling the web player's limiter holds too. */
+        const val LIMIT_CEILING = 0.8913f
+
+        private const val RAMP_SECONDS = 0.05f
+        private const val RELEASE_SECONDS = 0.25f
+        private const val PCM16_SCALE = 32768f
+        private const val PCM16_MAX = 32767f
+        private const val PCM16_BYTES = 2
+        private const val FLOAT_BYTES = 4
+    }
+}

android/app/src/main/java/com/fabledsword/minstrel/player/gain/ReplayGainStore.kt

@@ -0,0 +1,140 @@
+package com.fabledsword.minstrel.player.gain
+
+import com.fabledsword.minstrel.api.endpoints.ReplayGainApi
+import com.fabledsword.minstrel.cache.db.dao.CachedTrackDao
+import com.fabledsword.minstrel.connectivity.NetworkStatusController
+import com.fabledsword.minstrel.connectivity.ServerHealth
+import com.fabledsword.minstrel.di.ApplicationScope
+import kotlinx.coroutines.CancellationException
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.withTimeoutOrNull
+import retrofit2.Retrofit
+import retrofit2.create
+import timber.log.Timber
+import java.util.concurrent.ConcurrentHashMap
+import javax.inject.Inject
+import javax.inject.Singleton
+
+/**
+ * The gains the player levels by (M464 #5000), looked up per track and
+ * held for the life of the process. The audio thread reads them with [get];
+ * [request] fills them in the background.
+ *
+ * Sources, most to least preferred:
+ *  1. the library cache, synced with the gains, so cached audio levels
+ *     offline;
+ *  2. the server's replay-gain lookup, for a track not cached yet or
+ *     measured since the last sync;
+ *  3. none: the track plays as mastered, and the player picks the gain up
+ *     the moment it lands.
+ */
+@Singleton
+class ReplayGainStore internal constructor(
+    private val scope: CoroutineScope,
+    private val trackDao: CachedTrackDao,
+    private val api: ReplayGainApi,
+    private val serverHealth: () -> ServerHealth,
+    private val clock: () -> Long,
+) {
+    @Inject constructor(
+        @ApplicationScope scope: CoroutineScope,
+        trackDao: CachedTrackDao,
+        retrofit: Retrofit,
+        network: NetworkStatusController,
+    ) : this(
+        scope = scope,
+        trackDao = trackDao,
+        api = retrofit.create(),
+        serverHealth = { network.state.value },
+        clock = System::currentTimeMillis,
+    )
+
+    private val gains = ConcurrentHashMap<String, ReplayGain>()
+    private val inflight: MutableSet<String> = ConcurrentHashMap.newKeySet()
+
+    // When the server last said it had nothing for a track. Not cached for
+    // good: the backfill may measure it minutes later.
+    private val missedAt = ConcurrentHashMap<String, Long>()
+
+    /** The track's gains, or null while they are unknown. Safe from any thread. */
+    fun get(trackId: String): ReplayGain? = gains[trackId]
+
+    /** Starts loading gains for any of [trackIds] not already known or loading. */
+    fun request(trackIds: Collection<String>) {
+        val now = clock()
+        val wanted = trackIds.filter { id ->
+            !gains.containsKey(id) &&
+                (missedAt[id]?.let { now - it > MISS_RETRY_MS } ?: true) &&
+                inflight.add(id)
+        }
+        if (wanted.isEmpty()) return
+        scope.launch {
+            try {
+                load(wanted)
+            } finally {
+                inflight.removeAll(wanted.toSet())
+            }
+        }
+    }
+
+    internal suspend fun load(ids: List<String>) {
+        fromCache(ids)
+        val rest = ids.filter { !gains.containsKey(it) }
+        val health = serverHealth()
+        if (rest.isEmpty() || health == ServerHealth.Offline || health == ServerHealth.ServerDown) return
+        for (batch in rest.chunked(MAX_IDS_PER_REQUEST)) {
+            // A failed lookup leaves the batch unknown; the next request asks again.
+            if (!fromServer(batch)) return
+        }
+    }
+
+    private suspend fun fromCache(ids: List<String>) {
+        val rows = try {
+            trackDao.replayGains(ids)
+        } catch (e: CancellationException) {
+            throw e
+        } catch (
+            @Suppress("TooGenericExceptionCaught") e: Throwable,
+        ) {
+            Timber.w(e, "replay gain: cache read failed")
+            emptyList()
+        }
+        for (row in rows) {
+            // A cached row without a track gain is not an answer: the server
+            // may have measured the track since this device last synced.
+            if (row.trackGain == null) continue
+            gains[row.id] = ReplayGain(row.trackGain, row.trackPeak, row.albumGain, row.albumPeak)
+        }
+    }
+
+    /** Asks the server about [batch]; false when it could not be asked. */
+    private suspend fun fromServer(batch: List<String>): Boolean {
+        val res = try {
+            withTimeoutOrNull(REQUEST_TIMEOUT_MS) { api.getReplayGain(batch.joinToString(",")) }
+        } catch (e: CancellationException) {
+            throw e
+        } catch (
+            @Suppress("TooGenericExceptionCaught") e: Throwable,
+        ) {
+            Timber.w(e, "replay gain: lookup failed")
+            null
+        } ?: return false
+        val now = clock()
+        for (id in batch) {
+            val w = res.items[id]
+            if (w == null) {
+                missedAt[id] = now
+            } else {
+                gains[id] = ReplayGain(w.trackGain, w.trackPeak, w.albumGain, w.albumPeak)
+            }
+        }
+        return true
+    }
+
+    private companion object {
+        const val MAX_IDS_PER_REQUEST = 200 // the endpoint's limit
+        const val REQUEST_TIMEOUT_MS = 10_000L
+        const val MISS_RETRY_MS = 5 * 60_000L
+    }
+}

android/app/src/main/java/com/fabledsword/minstrel/player/output/SonosQueueLoader.kt

@@ -4,6 +4,8 @@ import com.fabledsword.minstrel.di.ApplicationScope
 import com.fabledsword.minstrel.models.TrackRef
 import com.fabledsword.minstrel.player.RemotePlayerState
 import com.fabledsword.minstrel.player.StreamTokenProvider
+import com.fabledsword.minstrel.player.gain.AlbumPosition
+import com.fabledsword.minstrel.player.gain.GainMath
 import com.fabledsword.minstrel.player.output.upnp.AVTransportClient
 import com.fabledsword.minstrel.player.output.upnp.SoapFaultException
 import com.fabledsword.minstrel.player.output.upnp.bareUdn
@@ -24,6 +26,11 @@ import javax.inject.Singleton
  * with its own failure modes, and it had grown large enough to hide one:
  * every write here is a SOAP call that can fail individually, and until
  * [verifyQueueLength] nothing ever read the result back.
+ *
+ * Every URL sent is a leveled one (M464 #5002): the server renders the track
+ * at the user's loudness gain, or hands back the plain stream when leveling
+ * is off. Renders are slow enough to matter, so the track playing and the
+ * one after it are rendered ahead; the rest render when the speaker asks.
  */
 @Singleton
 class SonosQueueLoader @Inject constructor(
@@ -32,6 +39,13 @@ class SonosQueueLoader @Inject constructor(
     private val activeUpnpHolder: ActiveUpnpHolder,
     private val remoteState: RemotePlayerState,
 ) {
+    // The queue as last sent to the renderer, for looking up the track after
+    // the one it is playing.
+    @Volatile private var sent: List<TrackRef> = emptyList()
+
+    // The renderer track the next one was last prerendered for.
+    @Volatile private var prerenderedAfter = 0
+
     suspend fun load(
         transport: AVTransportClient,
         route: OutputRoute,
@@ -46,8 +60,10 @@ class SonosQueueLoader @Inject constructor(
             "UPnP select: add %d initial tracks (currentIndex=%d, totalQueue=%d)",
             initialBatch.size, currentIndex, queue.size,
         )
-        initialBatch.forEachIndexed { idx, ref ->
-            val token = streamTokens.mint(ref.id)
+        sent = queue
+        prerenderedAfter = currentIndex + 1
+        initialBatch.indices.forEach { idx ->
+            val token = mint(queue, idx, prerender = idx == currentIndex)
             transport.addURIToQueue(
                 uri = token.url,
                 mime = token.mime,
@@ -64,12 +80,12 @@ class SonosQueueLoader @Inject constructor(
         Timber.w("UPnP select: Play")
         transport.play()
         Timber.w("UPnP select: initial done; backgrounding remainder")
-        val remaining = queue.drop(initialEnd)
         // Verify even when there is no tail to append: the initial batch is
         // sent the same way and can be dropped the same way.
         scope.launch {
-            if (remaining.isNotEmpty()) {
-                extendQueueOnSonos(transport, route, remaining, initialEnd)
+            prerender(queue, currentIndex + 1)
+            if (initialEnd < queue.size) {
+                extendQueueOnSonos(transport, route, queue, initialEnd)
             }
             verifyQueueLength(transport, route, queue)
         }
@@ -84,15 +100,16 @@ class SonosQueueLoader @Inject constructor(
     private suspend fun extendQueueOnSonos(
         transport: AVTransportClient,
         route: OutputRoute,
-        tracks: List<TrackRef>,
+        queue: List<TrackRef>,
         startPosition: Int,
     ) {
+        val count = queue.size - startPosition
         Timber.w(
             "UPnP extend: appending %d tracks starting at position %d",
-            tracks.size, startPosition + 1,
+            count, startPosition + 1,
         )
-        val succeeded = appendTracksToQueue(transport, route, tracks, startPosition)
-        Timber.w("UPnP extend: done (%d / %d appended)", succeeded, tracks.size)
+        val succeeded = appendTracksToQueue(transport, route, queue, startPosition)
+        Timber.w("UPnP extend: done (%d / %d appended)", succeeded, count)
     }
 
     /**
@@ -136,18 +153,17 @@ class SonosQueueLoader @Inject constructor(
                 Timber.w("UPnP verify: renderer holds %d tracks, queue intact", nrTracks)
                 return
             }
-            val missing = fullQueue.drop(nrTracks)
             Timber.w(
                 "UPnP verify: %s holds %d of %d tracks; appending %d missing (round %d)",
-                route.name, nrTracks, fullQueue.size, missing.size, round + 1,
+                route.name, nrTracks, fullQueue.size, fullQueue.size - nrTracks, round + 1,
             )
-            appendTracksToQueue(transport, route, missing, nrTracks)
+            appendTracksToQueue(transport, route, fullQueue, nrTracks)
         }
         Timber.w("UPnP verify: gave up repairing queue length on %s", route.name)
     }
 
     /**
-     * Append [tracks] at [startPosition] (0-based), returning how many landed.
+     * Append [queue] from [startPosition] (0-based) on, returning how many landed.
      * Tolerates individual AddURIToQueue failures — log and continue so some
      * tracks loaded is better than zero tracks loaded — and stops early after
      * [EXTEND_ABORT_AFTER_FAILURES] consecutive ones.
@@ -155,20 +171,20 @@ class SonosQueueLoader @Inject constructor(
     private suspend fun appendTracksToQueue(
         transport: AVTransportClient,
         route: OutputRoute,
-        tracks: List<TrackRef>,
+        queue: List<TrackRef>,
         startPosition: Int,
     ): Int {
         var consecutiveFailures = 0
         var succeeded = 0
         var aborted = false
-        for ((i, ref) in tracks.withIndex()) {
+        for (i in 0 until queue.size - startPosition) {
             if (aborted) break
             if (activeUpnpHolder.active.value?.routeId != route.id) {
                 Timber.w("UPnP extend: cancelled at offset %d (route changed)", i)
                 aborted = true
             } else {
                 val outcome = runCatching {
-                    val token = streamTokens.mint(ref.id)
+                    val token = mint(queue, startPosition + i)
                     transport.addURIToQueue(
                         uri = token.url,
                         mime = token.mime,
@@ -220,6 +236,7 @@ class SonosQueueLoader @Inject constructor(
         newQueue: List<TrackRef>,
     ): Boolean {
         val newIds = newQueue.map { it.id }
+        sent = newQueue
         if (oldIds == newIds) return true
         val prefixLen = commonPrefixLength(oldIds, newIds)
         val suffixLen = commonSuffixLength(
@@ -271,8 +288,7 @@ class SonosQueueLoader @Inject constructor(
             prefixLen + 1,
         )
         for (i in 0 until addedCount) {
-            val ref = newQueue[prefixLen + i]
-            val token = streamTokens.mint(ref.id)
+            val token = mint(newQueue, prefixLen + i)
             transport.addURIToQueue(
                 uri = token.url,
                 mime = token.mime,
@@ -283,6 +299,27 @@ class SonosQueueLoader @Inject constructor(
         }
     }
 
+    /**
+     * Called on every poll with the renderer's 1-based track number. When it
+     * moves, the track after it is rendered ahead, so the speaker's fetch of
+     * it finds the render ready.
+     */
+    fun onRendererTrack(trackNumber: Int) {
+        if (trackNumber <= 0 || trackNumber == prerenderedAfter) return
+        prerenderedAfter = trackNumber
+        val queue = sent
+        scope.launch { prerender(queue, trackNumber) }
+    }
+
+    private suspend fun prerender(queue: List<TrackRef>, index: Int) {
+        if (index !in queue.indices) return
+        runCatching { mint(queue, index, prerender = true) }
+            .onFailure { Timber.w(it, "UPnP prerender failed for %s", queue[index].id) }
+    }
+
+    private suspend fun mint(queue: List<TrackRef>, index: Int, prerender: Boolean = false) =
+        streamTokens.mint(queue[index].id, asAlbum = playingAsAlbum(queue, index), prerender = prerender)
+
     private fun commonPrefixLength(a: List<String>, b: List<String>): Int {
         val limit = minOf(a.size, b.size)
         for (i in 0 until limit) {
@@ -299,18 +336,33 @@ class SonosQueueLoader @Inject constructor(
         return limit
     }
 
-    private companion object {
+    companion object {
+        /**
+         * Whether [queue]'s track at [index] plays among its album in order,
+         * judged by its neighbours in the renderer's queue, which plays
+         * straight through.
+         */
+        internal fun playingAsAlbum(queue: List<TrackRef>, index: Int): Boolean =
+            GainMath.playingAsAlbum(
+                prev = queue.getOrNull(index - 1)?.let(::position),
+                cur = position(queue[index]),
+                next = queue.getOrNull(index + 1)?.let(::position),
+            )
+
+        private fun position(t: TrackRef) =
+            AlbumPosition(t.albumId.ifEmpty { null }, t.discNumber, t.trackNumber)
+
         // Abort the append loop after this many consecutive AddURIToQueue
         // failures; Sonos rate-limits burst adds and a wall of failures means
         // it has stopped accepting, not that the next one might land.
-        const val EXTEND_ABORT_AFTER_FAILURES = 3
-        const val EXTEND_THROTTLE_MS = 50L
+        private const val EXTEND_ABORT_AFTER_FAILURES = 3
+        private const val EXTEND_THROTTLE_MS = 50L
 
         // Verify/repair passes after a queue load. Two: one to catch the
         // common case (a rate-limit burst dropped a chunk), one to catch a
         // repair that itself got rate-limited. Beyond that the renderer is
         // refusing for a reason retrying won't fix, and the stall watchdog
         // becomes the backstop.
-        const val VERIFY_ROUNDS = 2
+        private const val VERIFY_ROUNDS = 2
     }
 }

android/app/src/main/java/com/fabledsword/minstrel/settings/data/NormalizationPrefs.kt

@@ -0,0 +1,55 @@
+package com.fabledsword.minstrel.settings.data
+
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+
+/**
+ * The user's loudness-normalization preference (M464 #4998). The server
+ * holds it, so this device, the web player and casts all level the same
+ * way; a copy is kept on the device so offline playback still applies it.
+ * Field names and values match `GET/PUT /api/me/normalization`.
+ *
+ * No constructor defaults, on purpose: the app's Json leaves out any field
+ * equal to its default (encodeDefaults is off), and the server refuses a PUT
+ * missing a field. Without defaults every field is always sent.
+ */
+@Serializable
+data class NormalizationPrefs(
+    val mode: NormalizationMode,
+    @SerialName("target_lufs") val targetLufs: Int,
+    val boost: NormalizationBoost,
+) {
+    companion object {
+        /** The targets the server accepts, quietest first. */
+        val TARGETS: List<Int> = listOf(-18, -16, -14)
+
+        /** Must match library.DefaultNormalizationPrefs on the server. */
+        val DEFAULT: NormalizationPrefs = NormalizationPrefs(
+            mode = NormalizationMode.AUTO,
+            targetLufs = -18,
+            boost = NormalizationBoost.HEADROOM,
+        )
+    }
+}
+
+@Serializable
+enum class NormalizationMode {
+    /** Tracks play at their mastered volume. */
+    @SerialName("off") OFF,
+
+    /** Album gain while an album plays in order, track gain otherwise. */
+    @SerialName("auto") AUTO,
+
+    @SerialName("track") TRACK,
+
+    @SerialName("album") ALBUM,
+}
+
+@Serializable
+enum class NormalizationBoost {
+    /** Quiet tracks are raised only as far as their true peak allows. */
+    @SerialName("headroom") HEADROOM,
+
+    /** Quiet tracks are raised all the way and a limiter holds the peaks. */
+    @SerialName("limiter") LIMITER,
+}

android/app/src/main/java/com/fabledsword/minstrel/settings/data/NormalizationRepository.kt

@@ -0,0 +1,67 @@
+package com.fabledsword.minstrel.settings.data
+
+import com.fabledsword.minstrel.api.endpoints.MeApi
+import com.fabledsword.minstrel.auth.AuthStore
+import com.fabledsword.minstrel.cache.db.dao.CachedMutationDao
+import com.fabledsword.minstrel.cache.mutations.MutationKind
+import com.fabledsword.minstrel.cache.mutations.MutationQueue
+import kotlinx.coroutines.CancellationException
+import kotlinx.coroutines.flow.StateFlow
+import retrofit2.Retrofit
+import retrofit2.create
+import timber.log.Timber
+import javax.inject.Inject
+import javax.inject.Singleton
+
+/**
+ * The user's loudness-normalization preference (M464 #4998). The device's
+ * copy lives in [AuthStore] so playback reads it offline; the server's copy
+ * is what other devices and casts use.
+ *
+ * Writes follow rule 100: the device shows the change at once, the PUT is
+ * best effort, and a failed PUT is queued for the MutationReplayer.
+ */
+@Singleton
+class NormalizationRepository @Inject constructor(
+    retrofit: Retrofit,
+    private val authStore: AuthStore,
+    private val mutationQueue: MutationQueue,
+    private val mutationDao: CachedMutationDao,
+) {
+    private val api: MeApi = retrofit.create()
+
+    val prefs: StateFlow<NormalizationPrefs> = authStore.normalization
+
+    /**
+     * Takes the server's value, unless a change made here is still queued:
+     * the server has not seen it yet, and taking its older value would undo
+     * the change on screen until the replay landed. Throws on a network
+     * failure; the device's copy then stands.
+     */
+    suspend fun refresh() {
+        val server = api.getNormalization()
+        if (mutationDao.hasPending(MutationKind.NORMALIZATION_SET)) return
+        authStore.setNormalization(server)
+    }
+
+    suspend fun set(next: NormalizationPrefs) {
+        authStore.setNormalization(next)
+        // An earlier change still queued would be replayed after this PUT
+        // and undo it. Queue behind it instead: the replayer sends only the
+        // newest queued preference.
+        if (mutationDao.hasPending(MutationKind.NORMALIZATION_SET)) {
+            mutationQueue.enqueueNormalizationSet(next)
+            return
+        }
+        try {
+            api.putNormalization(next)
+        } catch (e: CancellationException) {
+            throw e
+        } catch (
+            @Suppress("TooGenericExceptionCaught") e: Throwable,
+        ) {
+            Timber.i(e, "normalization: PUT failed; queued for replay")
+            mutationQueue.enqueueNormalizationSet(next)
+        }
+    }
+}

android/app/src/main/java/com/fabledsword/minstrel/settings/ui/AboutCardViewModel.kt

@@ -41,6 +41,10 @@ data class AboutUiState(
     // check must decide on. Held in state rather than read inline so a test
     // can drive the comparison without a BuildConfig.
     val installedCode: Long = BuildConfig.VERSION_CODE.toLong(),
+    // A debug build is signed with this machine's debug key, so the server's
+    // release-signed APK can never install over it (family idea #5103,
+    // practice 9). It updates from Android Studio instead.
+    val selfUpdates: Boolean = !BuildConfig.DEBUG,
     val isChecking: Boolean = false,
     val installStage: InstallStage = InstallStage.IDLE,
     val installMessage: String? = null,
@@ -67,7 +71,7 @@ class AboutCardViewModel @Inject constructor(
     val state: StateFlow<AboutUiState> = internal.asStateFlow()
 
     fun checkForUpdates() {
-        if (internal.value.isChecking) return
+        if (internal.value.isChecking || !internal.value.selfUpdates) return
         viewModelScope.launch {
             internal.update { it.copy(isChecking = true, installMessage = null) }
             val installed = internal.value.installedVersion

android/app/src/main/java/com/fabledsword/minstrel/settings/ui/NormalizationCard.kt

@@ -0,0 +1,143 @@
+package com.fabledsword.minstrel.settings.ui
+
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.material3.ElevatedCard
+import androidx.compose.material3.ExperimentalMaterial3Api
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.SegmentedButton
+import androidx.compose.material3.SegmentedButtonDefaults
+import androidx.compose.material3.SingleChoiceSegmentedButtonRow
+import androidx.compose.material3.Switch
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.unit.dp
+import androidx.hilt.navigation.compose.hiltViewModel
+import androidx.lifecycle.compose.collectAsStateWithLifecycle
+import com.fabledsword.minstrel.settings.data.NormalizationBoost
+import com.fabledsword.minstrel.settings.data.NormalizationMode
+import com.fabledsword.minstrel.settings.data.NormalizationPrefs
+
+/**
+ * Volume leveling (M464 #4998). The choice is stored on the server, so the
+ * web player and casts follow it too.
+ */
+@Composable
+fun NormalizationCard(viewModel: NormalizationViewModel = hiltViewModel()) {
+    val prefs by viewModel.prefs.collectAsStateWithLifecycle()
+    NormalizationCardContent(prefs = prefs, onChange = viewModel::update)
+}
+
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+internal fun NormalizationCardContent(
+    prefs: NormalizationPrefs,
+    onChange: (NormalizationPrefs) -> Unit,
+) {
+    ElevatedCard(modifier = Modifier.fillMaxWidth()) {
+        Column(
+            modifier = Modifier.padding(16.dp),
+            verticalArrangement = Arrangement.spacedBy(8.dp),
+        ) {
+            Text(
+                text = "Volume leveling",
+                style = MaterialTheme.typography.titleMedium,
+                color = MaterialTheme.colorScheme.onSurface,
+            )
+            Hint(modeHint(prefs.mode))
+            val modes = NormalizationMode.entries
+            SingleChoiceSegmentedButtonRow(modifier = Modifier.fillMaxWidth()) {
+                modes.forEachIndexed { index, mode ->
+                    SegmentedButton(
+                        selected = mode == prefs.mode,
+                        onClick = { onChange(prefs.copy(mode = mode)) },
+                        shape = SegmentedButtonDefaults.itemShape(
+                            index = index,
+                            count = modes.size,
+                        ),
+                    ) { Text(modeLabel(mode)) }
+                }
+            }
+            if (prefs.mode != NormalizationMode.OFF) {
+                TargetRow(prefs = prefs, onChange = onChange)
+                BoostRow(prefs = prefs, onChange = onChange)
+            }
+        }
+    }
+}
+
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+private fun TargetRow(prefs: NormalizationPrefs, onChange: (NormalizationPrefs) -> Unit) {
+    Text(
+        text = "Target loudness",
+        style = MaterialTheme.typography.bodyLarge,
+        color = MaterialTheme.colorScheme.onSurface,
+    )
+    val targets = NormalizationPrefs.TARGETS
+    SingleChoiceSegmentedButtonRow(modifier = Modifier.fillMaxWidth()) {
+        targets.forEachIndexed { index, lufs ->
+            SegmentedButton(
+                selected = lufs == prefs.targetLufs,
+                onClick = { onChange(prefs.copy(targetLufs = lufs)) },
+                shape = SegmentedButtonDefaults.itemShape(
+                    index = index,
+                    count = targets.size,
+                ),
+            ) { Text("$lufs LUFS") }
+        }
+    }
+}
+
+@Composable
+private fun BoostRow(prefs: NormalizationPrefs, onChange: (NormalizationPrefs) -> Unit) {
+    Row(verticalAlignment = Alignment.CenterVertically) {
+        Column(modifier = Modifier.weight(1f)) {
+            Text(
+                text = "Boost quiet tracks fully",
+                style = MaterialTheme.typography.bodyLarge,
+                color = MaterialTheme.colorScheme.onSurface,
+            )
+            Hint("A limiter catches the peaks.")
+        }
+        Spacer(Modifier.size(12.dp))
+        Switch(
+            checked = prefs.boost == NormalizationBoost.LIMITER,
+            onCheckedChange = { on ->
+                val boost = if (on) NormalizationBoost.LIMITER else NormalizationBoost.HEADROOM
+                onChange(prefs.copy(boost = boost))
+            },
+        )
+    }
+}
+
+@Composable
+private fun Hint(text: String) {
+    Text(
+        text = text,
+        style = MaterialTheme.typography.bodySmall,
+        color = MaterialTheme.colorScheme.onSurfaceVariant,
+    )
+}
+
+private fun modeLabel(mode: NormalizationMode): String = when (mode) {
+    NormalizationMode.OFF -> "Off"
+    NormalizationMode.AUTO -> "Auto"
+    NormalizationMode.TRACK -> "Track"
+    NormalizationMode.ALBUM -> "Album"
+}
+
+private fun modeHint(mode: NormalizationMode): String = when (mode) {
+    NormalizationMode.OFF -> "Tracks play at their mastered volume."
+    NormalizationMode.AUTO -> "Album gain for whole albums, track gain otherwise."
+    NormalizationMode.TRACK -> "Every track at the same loudness."
+    NormalizationMode.ALBUM -> "Albums keep their own quiet and loud tracks."
+}

android/app/src/main/java/com/fabledsword/minstrel/settings/ui/NormalizationViewModel.kt

@@ -0,0 +1,44 @@
+package com.fabledsword.minstrel.settings.ui
+
+import androidx.lifecycle.ViewModel
+import androidx.lifecycle.viewModelScope
+import com.fabledsword.minstrel.settings.data.NormalizationPrefs
+import com.fabledsword.minstrel.settings.data.NormalizationRepository
+import dagger.hilt.android.lifecycle.HiltViewModel
+import kotlinx.coroutines.CancellationException
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.launch
+import timber.log.Timber
+import javax.inject.Inject
+
+/**
+ * Backs the Volume leveling card. Shows the device's copy straight away and
+ * refreshes it from the server on open, so a change made on the web shows
+ * here too.
+ */
+@HiltViewModel
+class NormalizationViewModel @Inject constructor(
+    private val repository: NormalizationRepository,
+) : ViewModel() {
+
+    val prefs: StateFlow<NormalizationPrefs> = repository.prefs
+
+    init {
+        viewModelScope.launch {
+            try {
+                repository.refresh()
+            } catch (e: CancellationException) {
+                throw e
+            } catch (
+                @Suppress("TooGenericExceptionCaught") e: Throwable,
+            ) {
+                // Offline: the device's copy stands.
+                Timber.i(e, "normalization: refresh failed")
+            }
+        }
+    }
+
+    fun update(next: NormalizationPrefs) {
+        viewModelScope.launch { repository.set(next) }
+    }
+}

android/app/src/main/java/com/fabledsword/minstrel/settings/ui/PasswordViewModel.kt

@@ -57,7 +57,7 @@ class PasswordViewModel @Inject constructor(
             try {
                 repository.changePassword(current = s.current, next = s.next)
                 internal.update {
-                    PasswordUiState(message = "Password changed.")
+                    PasswordUiState(message = "Password changed. Your other devices have been signed out.")
                 }
             } catch (
                 @Suppress("TooGenericExceptionCaught") e: Throwable,

android/app/src/main/java/com/fabledsword/minstrel/settings/ui/SettingsScreen.kt

@@ -161,6 +161,7 @@ private fun SettingsList(
                 onToggle = onToggleDiagnostics,
             )
         }
+        NormalizationCard()
         AppearanceCard(themeMode = themeMode, onPick = onPickTheme)
         StorageCard()
         AboutCard()
@@ -382,6 +383,14 @@ private fun AboutCard(viewModel: AboutCardViewModel = hiltViewModel()) {
 
 @Composable
 private fun UpdateControls(state: AboutUiState, viewModel: AboutCardViewModel) {
+    if (!state.selfUpdates) {
+        Text(
+            text = "Debug build: updates install from Android Studio.",
+            style = MaterialTheme.typography.bodySmall,
+            color = MaterialTheme.colorScheme.onSurfaceVariant,
+        )
+        return
+    }
     UpdateCheckLine(result = state.result)
     Button(
         onClick = viewModel::checkForUpdates,

android/app/src/main/java/com/fabledsword/minstrel/update/data/UpdateBannerController.kt

@@ -29,6 +29,9 @@ private const val POLL_INTERVAL_MS = 24 * 60 * 60 * 1000L
  * restart re-shows it, which is acceptable nudging for v1 (matches
  * Flutter). Server 404 / network errors stay silent. Constructed at
  * launch via the construct-the-singleton trick in `MinstrelApplication`.
+ *
+ * A debug build never polls: it is signed with a local debug key, so the
+ * server's release-signed APK could never install over it (#5103).
  */
 @Singleton
 class UpdateBannerController @Inject constructor(
@@ -45,6 +48,10 @@ class UpdateBannerController @Inject constructor(
         }.stateIn(scope, SharingStarted.Eagerly, null)
 
     init {
+        if (!BuildConfig.DEBUG) startPolling()
+    }
+
+    private fun startPolling() {
         scope.launch {
             while (true) {
                 runOnce()

android/app/src/main/res/xml/network_security_config.xml

@@ -17,8 +17,12 @@
   hostnames rather than CIDR ranges, and both sets of hosts above are unknowable
   until runtime. So a permissive base-config is an honest description of our
   situation — the gain over the manifest attribute is that the reasoning now
-  lives somewhere, and there is one place to tighten if a future settings screen
-  can distinguish a LAN server from a WAN one.
+  lives somewhere.
+
+  The LAN/WAN line this file cannot draw is drawn in code instead:
+  api/CleartextGuard.kt refuses plain http:// to the Minstrel server whenever
+  the connection lands on a public address (family baseline #5105, practice
+  13). LAN servers and UPnP speakers are unaffected.
 
   Worth stating because it looks worse than it is: this is NOT a tamper risk for
   the in-app updater. An APK altered in transit and re-signed is rejected by the

android/app/src/test/java/com/fabledsword/minstrel/api/AuthCookieInterceptorTest.kt

@@ -1,6 +1,7 @@
 package com.fabledsword.minstrel.api
 
 import com.fabledsword.minstrel.auth.AuthStore
+import com.fabledsword.minstrel.auth.FakeSessionVault
 import com.fabledsword.minstrel.cache.db.dao.AuthSessionDao
 import io.mockk.coEvery
 import io.mockk.every
@@ -43,7 +44,7 @@ class AuthCookieInterceptorTest {
                 coEvery { setSessionCookie(any()) } returns Unit
                 coEvery { setBaseUrl(any()) } returns Unit
             }
-        authStore = AuthStore(dao, TestScope(UnconfinedTestDispatcher()))
+        authStore = AuthStore(dao, FakeSessionVault(), TestScope(UnconfinedTestDispatcher()))
 
         // BaseUrlInterceptor rewrites placeholder.invalid → mock server.
         // AuthCookieInterceptor scopes its attach + clear behavior to

android/app/src/test/java/com/fabledsword/minstrel/api/BaseUrlInterceptorTest.kt

@@ -1,6 +1,7 @@
 package com.fabledsword.minstrel.api
 
 import com.fabledsword.minstrel.auth.AuthStore
+import com.fabledsword.minstrel.auth.FakeSessionVault
 import com.fabledsword.minstrel.cache.db.dao.AuthSessionDao
 import io.mockk.coEvery
 import io.mockk.every
@@ -38,7 +39,7 @@ class BaseUrlInterceptorTest {
                 coEvery { setSessionCookie(any()) } returns Unit
                 coEvery { setBaseUrl(any()) } returns Unit
             }
-        authStore = AuthStore(dao, TestScope(UnconfinedTestDispatcher()))
+        authStore = AuthStore(dao, FakeSessionVault(), TestScope(UnconfinedTestDispatcher()))
     }
 
     @AfterEach

android/app/src/test/java/com/fabledsword/minstrel/api/CleartextGuardTest.kt

@@ -0,0 +1,89 @@
+package com.fabledsword.minstrel.api
+
+import okhttp3.OkHttpClient
+import okhttp3.Request
+import okhttp3.mockwebserver.MockResponse
+import okhttp3.mockwebserver.MockWebServer
+import org.junit.jupiter.api.AfterEach
+import org.junit.jupiter.api.BeforeEach
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.assertThrows
+import java.net.InetAddress
+import kotlin.test.assertEquals
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+
+/** Plain http:// to the Minstrel server only on a private address (#5105, practice 13). */
+class CleartextGuardTest {
+    private lateinit var server: MockWebServer
+
+    @BeforeEach
+    fun setup() {
+        server = MockWebServer().apply { start() }
+    }
+
+    @AfterEach
+    fun teardown() {
+        server.shutdown()
+    }
+
+    private fun ip(s: String) = InetAddress.getByName(s)
+
+    @Test
+    fun `home network and overlay addresses may use plain http`() {
+        for (a in listOf(
+            "127.0.0.1", "10.1.2.3", "172.16.0.9", "172.31.255.1", "192.168.1.20",
+            "169.254.3.4", "100.64.0.1", "100.127.255.254", "::1", "fd12:3456::1", "fe80::1",
+        )) {
+            assertTrue(CleartextPolicy.allows(ip(a)), "$a should be allowed")
+        }
+    }
+
+    @Test
+    fun `public addresses may not`() {
+        for (a in listOf(
+            "8.8.8.8", "172.32.0.1", "100.128.0.1", "100.63.255.255", "203.0.113.5",
+            "2001:db8::1", "2606:4700::1111",
+        )) {
+            assertFalse(CleartextPolicy.allows(ip(a)), "$a should be refused")
+        }
+    }
+
+    private fun client(allows: Boolean) = OkHttpClient.Builder()
+        .addNetworkInterceptor(CleartextGuardInterceptor { allows })
+        .build()
+
+    private fun serverRequest() = Request.Builder()
+        .url(server.url("/api/auth/login"))
+        .tag(MinstrelServerRequest::class.java, MinstrelServerRequest)
+        .build()
+
+    @Test
+    fun `a refused server request sends nothing`() {
+        server.enqueue(MockResponse().setResponseCode(200))
+        assertThrows<CleartextToPublicHostException> {
+            client(allows = false).newCall(serverRequest()).execute()
+        }
+        assertEquals(0, server.requestCount, "the request reached the server")
+    }
+
+    @Test
+    fun `an allowed server request goes through`() {
+        server.enqueue(MockResponse().setResponseCode(200))
+        client(allows = true).newCall(serverRequest()).execute().use { assertEquals(200, it.code) }
+        assertEquals(1, server.requestCount)
+    }
+
+    @Test
+    fun `requests not bound for the Minstrel server are left alone`() {
+        server.enqueue(MockResponse().setResponseCode(200))
+        client(allows = false).newCall(Request.Builder().url(server.url("/art.jpg")).build())
+            .execute().use { assertEquals(200, it.code) }
+    }
+
+    @Test
+    fun `the refusal has its own message`() {
+        val msg = ErrorCopy.fromThrowable(CleartextToPublicHostException("music.example.com"))
+        assertTrue(msg.contains("https://"), msg)
+    }
+}

android/app/src/test/java/com/fabledsword/minstrel/api/ErrorCopyTest.kt

@@ -0,0 +1,60 @@
+package com.fabledsword.minstrel.api
+
+import okhttp3.MediaType.Companion.toMediaType
+import okhttp3.ResponseBody.Companion.toResponseBody
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Test
+import retrofit2.HttpException
+import retrofit2.Response
+import java.io.IOException
+
+class ErrorCopyTest {
+    private fun httpError(status: Int, body: String): HttpException =
+        HttpException(
+            Response.error<Unit>(status, body.toResponseBody("application/json".toMediaType())),
+        )
+
+    @Test
+    fun libraryNotWritableAppendsTheServerDetail() {
+        val detail = "Minstrel runs as uid 1000, gid 1000 and cannot delete from /music/A " +
+            "(read-only file system). The library mount must be writable by that user. " +
+            "Nothing was deleted."
+        val e = httpError(409, """{"error":{"code":"library_not_writable","message":"$detail"}}""")
+
+        assertEquals(
+            "${ErrorCopy.messageFor("library_not_writable")} $detail",
+            ErrorCopy.fromThrowable(e),
+        )
+    }
+
+    @Test
+    fun detailCodeWithoutAMessageShowsTheCopyAlone() {
+        val e = httpError(409, """{"error":{"code":"library_not_writable","message":""}}""")
+
+        assertEquals(ErrorCopy.messageFor("library_not_writable"), ErrorCopy.fromThrowable(e))
+    }
+
+    // Server messages are usually internal detail; appending them for every
+    // code would leak driver errors into snackbars. This pins the scope.
+    @Test
+    fun otherCodesNeverCarryTheServerMessage() {
+        val e = httpError(404, """{"error":{"code":"track_not_found","message":"pgx: no rows"}}""")
+
+        assertEquals(ErrorCopy.messageFor("track_not_found"), ErrorCopy.fromThrowable(e))
+    }
+
+    @Test
+    fun anUnparseableBodyFallsBackToUnknown() {
+        val e = httpError(500, "not json")
+
+        assertEquals(ErrorCopy.messageFor("unknown"), ErrorCopy.fromThrowable(e))
+    }
+
+    @Test
+    fun transportFailureMapsToConnectionRefused() {
+        assertEquals(
+            ErrorCopy.messageFor("connection_refused"),
+            ErrorCopy.fromThrowable(IOException("refused")),
+        )
+    }
+}

android/app/src/test/java/com/fabledsword/minstrel/auth/AuthStoreSessionVaultTest.kt

@@ -0,0 +1,111 @@
+package com.fabledsword.minstrel.auth
+
+import com.fabledsword.minstrel.cache.db.dao.AuthSessionDao
+import com.fabledsword.minstrel.cache.db.entities.AuthSessionEntity
+import io.mockk.coEvery
+import io.mockk.coVerify
+import io.mockk.every
+import io.mockk.mockk
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.flow.flowOf
+import kotlinx.coroutines.test.StandardTestDispatcher
+import kotlinx.coroutines.test.TestScope
+import kotlinx.coroutines.test.UnconfinedTestDispatcher
+import kotlinx.coroutines.test.advanceUntilIdle
+import kotlinx.coroutines.test.runTest
+import org.junit.jupiter.api.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertNull
+
+/**
+ * The session cookie moved out of the Room row into a Keystore-backed vault
+ * (M462 #4985). What matters is that nobody is signed out by it: an install
+ * upgrading with a cookie in the row keeps it, a device whose Keystore will
+ * not work keeps the old storage, and a sign-in or 401 that lands while the
+ * one-time move runs is never overwritten by the value it read.
+ */
+@OptIn(ExperimentalCoroutinesApi::class)
+class AuthStoreSessionVaultTest {
+    /** A DAO whose single row holds [legacyCookie] in its sessionCookie column. */
+    private class RowDao(var legacyCookie: String?) {
+        val dao: AuthSessionDao = mockk {
+            every { observe() } returns flowOf(null)
+            coEvery { get() } answers {
+                AuthSessionEntity(baseUrl = "http://music.local", sessionCookie = legacyCookie)
+            }
+            coEvery { upsert(any()) } answers { legacyCookie = firstArg<AuthSessionEntity>().sessionCookie }
+            coEvery { setSessionCookie(any()) } answers { legacyCookie = firstArg() }
+        }
+    }
+
+    @Test
+    fun `an upgrading install keeps its session, moved out of the row into the vault`() = runTest {
+        val row = RowDao(legacyCookie = "session=abc")
+        val vault = FakeSessionVault()
+
+        val store = AuthStore(row.dao, vault, TestScope(UnconfinedTestDispatcher(testScheduler)))
+        store.awaitSessionHydrated()
+
+        assertEquals("session=abc", store.sessionCookie.value)
+        assertEquals("session=abc", vault.stored)
+        assertNull(row.legacyCookie, "the plain-text copy must be cleared from the row")
+    }
+
+    @Test
+    fun `a cookie already in the vault is loaded without touching the row`() = runTest {
+        val row = RowDao(legacyCookie = null)
+        val vault = FakeSessionVault(stored = "session=xyz")
+
+        val store = AuthStore(row.dao, vault, TestScope(UnconfinedTestDispatcher(testScheduler)))
+        store.awaitSessionHydrated()
+
+        assertEquals("session=xyz", store.sessionCookie.value)
+        assertEquals(0, vault.writes)
+        coVerify(exactly = 0) { row.dao.setSessionCookie(any()) }
+    }
+
+    @Test
+    fun `when the Keystore will not work the cookie stays in the row instead of being lost`() = runTest {
+        val row = RowDao(legacyCookie = "session=abc")
+        val vault = FakeSessionVault(available = false)
+
+        val store = AuthStore(row.dao, vault, TestScope(UnconfinedTestDispatcher(testScheduler)))
+        store.awaitSessionHydrated()
+        assertEquals("session=abc", store.sessionCookie.value)
+        assertEquals("session=abc", row.legacyCookie)
+
+        store.setSessionCookie("session=new")
+        assertEquals("session=new", row.legacyCookie, "fallback writes go to the row")
+    }
+
+    @Test
+    fun `sign-in and sign-out write the vault, and never the row`() = runTest {
+        val row = RowDao(legacyCookie = null)
+        val vault = FakeSessionVault()
+        val store = AuthStore(row.dao, vault, TestScope(UnconfinedTestDispatcher(testScheduler)))
+        store.awaitSessionHydrated()
+
+        store.setSessionCookie("session=new")
+        assertEquals("session=new", vault.stored)
+        assertNull(row.legacyCookie)
+
+        store.setSessionCookie(null)
+        assertNull(vault.stored)
+        assertNull(store.sessionCookie.value)
+    }
+
+    @Test
+    fun `a sign-out that lands before hydration finishes is not undone by it`() = runTest {
+        val row = RowDao(legacyCookie = "session=stale")
+        val vault = FakeSessionVault()
+        val scope = TestScope(StandardTestDispatcher(testScheduler))
+
+        // Hydration is queued but has not run; a 401 clears the session first.
+        val store = AuthStore(row.dao, vault, scope)
+        store.setSessionCookie(null)
+        scope.advanceUntilIdle()
+
+        assertNull(store.sessionCookie.value, "hydration must not resurrect the stale cookie")
+        assertNull(vault.stored)
+    }
+}

android/app/src/test/java/com/fabledsword/minstrel/auth/FakeSessionVault.kt

@@ -0,0 +1,23 @@
+package com.fabledsword.minstrel.auth
+
+/**
+ * In-memory [SessionVault] for JVM tests: the Android Keystore has no JVM
+ * implementation. [available] = false stands in for a device whose Keystore
+ * refuses to work, so callers' fallback paths can be exercised.
+ */
+class FakeSessionVault(
+    var stored: String? = null,
+    var available: Boolean = true,
+) : SessionVault {
+    var writes = 0
+        private set
+
+    override fun read(): String? = if (available) stored else null
+
+    override fun write(value: String?): Boolean {
+        if (!available) return false
+        writes++
+        stored = value
+        return true
+    }
+}

android/app/src/test/java/com/fabledsword/minstrel/auth/SealedBoxTest.kt

@@ -0,0 +1,48 @@
+package com.fabledsword.minstrel.auth
+
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.assertThrows
+import java.util.Base64
+import javax.crypto.KeyGenerator
+import javax.crypto.SecretKey
+import kotlin.test.assertEquals
+import kotlin.test.assertFalse
+import kotlin.test.assertNotEquals
+
+/**
+ * The sealing half of the session vault, with an ordinary JVM AES key in
+ * place of the Keystore one (the Keystore has no JVM implementation).
+ */
+class SealedBoxTest {
+    private fun newKey(): SecretKey = KeyGenerator.getInstance("AES").apply { init(256) }.generateKey()
+
+    @Test
+    fun `round-trips a cookie`() {
+        val key = newKey()
+        assertEquals("session=abc", SealedBox.open(key, SealedBox.seal(key, "session=abc")))
+    }
+
+    @Test
+    fun `the stored form does not contain the cookie, and differs every time`() {
+        val key = newKey()
+        val first = SealedBox.seal(key, "session=abc")
+        val second = SealedBox.seal(key, "session=abc")
+        assertNotEquals(first, second, "a fresh IV per seal")
+        val decoded = String(Base64.getDecoder().decode(first), Charsets.ISO_8859_1)
+        assertFalse(decoded.contains("session=abc"), "plaintext visible in the sealed value")
+    }
+
+    @Test
+    fun `a tampered value does not open`() {
+        val key = newKey()
+        val bytes = Base64.getDecoder().decode(SealedBox.seal(key, "session=abc"))
+        bytes[bytes.size - 1] = (bytes[bytes.size - 1].toInt() xor 1).toByte()
+        assertThrows<Exception> { SealedBox.open(key, Base64.getEncoder().encodeToString(bytes)) }
+    }
+
+    @Test
+    fun `a value sealed under another key does not open`() {
+        val sealed = SealedBox.seal(newKey(), "session=abc")
+        assertThrows<Exception> { SealedBox.open(newKey(), sealed) }
+    }
+}

android/app/src/test/java/com/fabledsword/minstrel/cache/mutations/SupersededToggleIdsTest.kt

@@ -1,6 +1,8 @@
 package com.fabledsword.minstrel.cache.mutations
 
 import com.fabledsword.minstrel.cache.db.entities.CachedMutationEntity
+import com.fabledsword.minstrel.settings.data.NormalizationMode
+import com.fabledsword.minstrel.settings.data.NormalizationPrefs
 import kotlinx.serialization.json.Json
 import org.junit.jupiter.api.Test
 import kotlin.test.assertEquals
@@ -129,4 +131,26 @@ class SupersededToggleIdsTest {
     fun `an empty queue collapses nothing`() {
         assertTrue(supersededToggleIds(emptyList(), json).isEmpty())
     }
+
+    private fun normalizationRow(id: Long, mode: NormalizationMode) = CachedMutationEntity(
+        id = id,
+        kind = MutationKind.NORMALIZATION_SET,
+        payload = json.encodeToString(
+            NormalizationPrefs.serializer(),
+            NormalizationPrefs.DEFAULT.copy(mode = mode),
+        ),
+    )
+
+    // There is one preference per user, so any two queued changes to it
+    // collapse, and only the newest is sent (#4998).
+    @Test
+    fun `only the newest queued normalization change survives`() {
+        val rows = listOf(
+            normalizationRow(1, NormalizationMode.TRACK),
+            snoozeRow(2, "mb-a", desiredSnoozed = true),
+            normalizationRow(3, NormalizationMode.OFF),
+            normalizationRow(4, NormalizationMode.ALBUM),
+        )
+        assertEquals(setOf(1L, 3L), supersededToggleIds(rows, json))
+    }
 }

android/app/src/test/java/com/fabledsword/minstrel/player/gain/GainMathTest.kt

@@ -0,0 +1,111 @@
+package com.fabledsword.minstrel.player.gain
+
+import com.fabledsword.minstrel.settings.data.NormalizationBoost
+import com.fabledsword.minstrel.settings.data.NormalizationMode
+import com.fabledsword.minstrel.settings.data.NormalizationPrefs
+import org.junit.jupiter.api.Test
+import kotlin.math.log10
+import kotlin.test.assertEquals
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+
+/** Mirrors web/src/lib/player/gain.test.ts: both players must level alike. */
+class GainMathTest {
+
+    private fun prefs(
+        mode: NormalizationMode = NormalizationMode.AUTO,
+        target: Int = -18,
+        boost: NormalizationBoost = NormalizationBoost.HEADROOM,
+    ) = NormalizationPrefs(mode = mode, targetLufs = target, boost = boost)
+
+    private val g = ReplayGain(trackGain = -6f, trackPeak = 1f, albumGain = -4f, albumPeak = 1f)
+
+    @Test
+    fun `off and unmeasured tracks play as mastered`() {
+        assertEquals(0f, GainMath.gainDb(prefs(mode = NormalizationMode.OFF), g, false))
+        assertEquals(0f, GainMath.gainDb(prefs(), null, false))
+        assertEquals(0f, GainMath.gainDb(prefs(), ReplayGain.NONE, false))
+    }
+
+    @Test
+    fun `mode picks the gain and auto follows album play`() {
+        assertEquals(-6f, GainMath.gainDb(prefs(mode = NormalizationMode.TRACK), g, true))
+        assertEquals(-4f, GainMath.gainDb(prefs(mode = NormalizationMode.ALBUM), g, false))
+        assertEquals(-4f, GainMath.gainDb(prefs(), g, true))
+        assertEquals(-6f, GainMath.gainDb(prefs(), g, false))
+    }
+
+    @Test
+    fun `album gain falls back to track gain until the album is measured`() {
+        val partial = ReplayGain(trackGain = -6f, trackPeak = 1f, albumGain = null, albumPeak = null)
+        assertEquals(-6f, GainMath.gainDb(prefs(mode = NormalizationMode.ALBUM), partial, true))
+    }
+
+    @Test
+    fun `a louder target raises every gain by the difference`() {
+        assertEquals(-2f, GainMath.gainDb(prefs(mode = NormalizationMode.TRACK, target = -14), g, false))
+    }
+
+    @Test
+    fun `headroom stops a boost 1 dB under the true peak and the limiter lets it through`() {
+        val quiet = ReplayGain(trackGain = 8f, trackPeak = 0.5f, albumGain = null, albumPeak = null)
+        val headroom = GainMath.gainDb(prefs(mode = NormalizationMode.TRACK), quiet, false)
+        assertEquals(-1f - 20f * log10(0.5f), headroom, 1e-4f)
+        val limited = GainMath.gainDb(
+            prefs(mode = NormalizationMode.TRACK, boost = NormalizationBoost.LIMITER),
+            quiet,
+            false,
+        )
+        assertEquals(8f, limited)
+    }
+
+    @Test
+    fun `no boost passes the cap`() {
+        val silent = ReplayGain(trackGain = 30f, trackPeak = 0.001f, albumGain = null, albumPeak = null)
+        val db = GainMath.gainDb(
+            prefs(mode = NormalizationMode.TRACK, boost = NormalizationBoost.LIMITER),
+            silent,
+            false,
+        )
+        assertEquals(GainMath.MAX_BOOST_DB, db)
+    }
+
+    @Test
+    fun `cuts are never limited by the peak`() {
+        val hot = ReplayGain(trackGain = -9f, trackPeak = 1.4f, albumGain = null, albumPeak = null)
+        assertEquals(-9f, GainMath.gainDb(prefs(mode = NormalizationMode.TRACK), hot, false))
+    }
+
+    private fun pos(album: String, track: Int?, disc: Int? = 1) = AlbumPosition(album, disc, track)
+
+    @Test
+    fun `in-order neighbours from the same album are album play`() {
+        assertTrue(GainMath.playingAsAlbum(null, pos("x", 1), pos("x", 2)))
+        assertTrue(GainMath.playingAsAlbum(pos("x", 1), pos("x", 2), pos("x", 3)))
+        assertTrue(GainMath.playingAsAlbum(pos("x", 2), pos("x", 3), null))
+    }
+
+    @Test
+    fun `a shuffled album, a mix and a lone track are not album play`() {
+        assertFalse(GainMath.playingAsAlbum(null, pos("x", 3), pos("x", 1)))
+        assertFalse(GainMath.playingAsAlbum(null, pos("x", 1), pos("y", 2)))
+        assertFalse(GainMath.playingAsAlbum(null, pos("x", 1), null))
+    }
+
+    @Test
+    fun `disc order counts`() {
+        assertTrue(GainMath.playingAsAlbum(pos("x", 12, disc = 1), pos("x", 1, disc = 2), null))
+    }
+
+    @Test
+    fun `a neighbour without a track number is not evidence of order`() {
+        assertFalse(GainMath.playingAsAlbum(pos("x", null), pos("x", 3), null))
+        assertFalse(GainMath.playingAsAlbum(null, pos("x", null), pos("x", null)))
+    }
+
+    @Test
+    fun `dbToLinear`() {
+        assertEquals(1f, GainMath.dbToLinear(0f))
+        assertEquals(0.1f, GainMath.dbToLinear(-20f), 1e-6f)
+    }
+}

android/app/src/test/java/com/fabledsword/minstrel/player/gain/GainStageTest.kt

@@ -0,0 +1,73 @@
+package com.fabledsword.minstrel.player.gain
+
+import org.junit.jupiter.api.Test
+import java.nio.ByteBuffer
+import java.nio.ByteOrder
+import kotlin.math.abs
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+class GainStageTest {
+
+    private fun floats(vararg v: Float): ByteBuffer =
+        ByteBuffer.allocateDirect(v.size * 4).order(ByteOrder.nativeOrder()).apply {
+            v.forEach { putFloat(it) }
+            flip()
+        }
+
+    private fun shorts(vararg v: Short): ByteBuffer =
+        ByteBuffer.allocateDirect(v.size * 2).order(ByteOrder.nativeOrder()).apply {
+            v.forEach { putShort(it) }
+            flip()
+        }
+
+    private fun runFloat(stage: GainStage, input: ByteBuffer, target: Float, limiting: Boolean): FloatArray {
+        val out = ByteBuffer.allocateDirect(input.remaining()).order(ByteOrder.nativeOrder())
+        stage.process(input, out, channels = 2, isFloat = true, target = target, limiting = limiting)
+        out.flip()
+        return FloatArray(out.remaining() / 4) { out.float }
+    }
+
+    @Test
+    fun `a stream that starts at its gain is scaled from the first sample`() {
+        val stage = GainStage().apply { reset(sampleRate = 44_100, channels = 2, startGain = 0.5f) }
+        val out = runFloat(stage, floats(0.8f, -0.4f), target = 0.5f, limiting = false)
+        assertEquals(0.4f, out[0], 1e-6f)
+        assertEquals(-0.2f, out[1], 1e-6f)
+    }
+
+    @Test
+    fun `a changed target ramps rather than steps`() {
+        val stage = GainStage().apply { reset(sampleRate = 44_100, channels = 2, startGain = 1f) }
+        val n = 44_100 // one second of stereo frames
+        val input = floats(*FloatArray(n * 2) { 0.5f })
+        val out = runFloat(stage, input, target = 0.5f, limiting = false)
+        assertTrue(out[0] > 0.49f, "first frame barely moved: ${out[0]}")
+        assertEquals(0.25f, out.last(), 1e-3f)
+    }
+
+    @Test
+    fun `the limiter holds a boosted peak at -1 dBFS`() {
+        val stage = GainStage().apply { reset(sampleRate = 44_100, channels = 2, startGain = 4f) }
+        val out = runFloat(stage, floats(0.9f, -0.9f, 0.1f, 0.1f), target = 4f, limiting = true)
+        out.forEach { assertTrue(abs(it) <= GainStage.LIMIT_CEILING + 1e-6f, "sample $it over the ceiling") }
+    }
+
+    @Test
+    fun `without the limiter a boost is clamped to full scale, 16-bit included`() {
+        val stage = GainStage().apply { reset(sampleRate = 44_100, channels = 2, startGain = 4f) }
+        val input = shorts(20_000, -20_000)
+        val out = ByteBuffer.allocateDirect(4).order(ByteOrder.nativeOrder())
+        stage.process(input, out, channels = 2, isFloat = false, target = 4f, limiting = false)
+        out.flip()
+        assertEquals(Short.MAX_VALUE, out.short)
+        assertEquals((-Short.MAX_VALUE).toShort(), out.short)
+    }
+
+    @Test
+    fun `unity is a pass-through`() {
+        val stage = GainStage().apply { reset(sampleRate = 44_100, channels = 2, startGain = 1f) }
+        assertTrue(stage.isUnity(target = 1f, limiting = false))
+        assertTrue(!stage.isUnity(target = 1f, limiting = true))
+    }
+}

android/app/src/test/java/com/fabledsword/minstrel/player/gain/ReplayGainStoreTest.kt

@@ -0,0 +1,74 @@
+package com.fabledsword.minstrel.player.gain
+
+import com.fabledsword.minstrel.api.endpoints.ReplayGainApi
+import com.fabledsword.minstrel.cache.db.dao.CachedReplayGain
+import com.fabledsword.minstrel.cache.db.dao.CachedTrackDao
+import com.fabledsword.minstrel.connectivity.ServerHealth
+import com.fabledsword.minstrel.models.wire.ReplayGainResponseWire
+import com.fabledsword.minstrel.models.wire.ReplayGainWire
+import io.mockk.coEvery
+import io.mockk.coVerify
+import io.mockk.mockk
+import kotlinx.coroutines.test.TestScope
+import kotlinx.coroutines.test.runTest
+import org.junit.jupiter.api.Test
+import java.io.IOException
+import kotlin.test.assertEquals
+import kotlin.test.assertNull
+
+/** The fallback ladder: the library cache, then the server, then nothing. */
+class ReplayGainStoreTest {
+    private val dao: CachedTrackDao = mockk()
+    private val api: ReplayGainApi = mockk()
+    private var health = ServerHealth.Healthy
+
+    private fun store() = ReplayGainStore(
+        scope = TestScope(),
+        trackDao = dao,
+        api = api,
+        serverHealth = { health },
+        clock = { 0L },
+    )
+
+    @Test
+    fun `cached gains are used and only the rest are asked of the server`() = runTest {
+        coEvery { dao.replayGains(listOf("a", "b", "c")) } returns listOf(
+            CachedReplayGain("a", trackGain = -6f, trackPeak = 1f, albumGain = -4f, albumPeak = 1f),
+            // Cached but unmeasured at the last sync: the server may know more.
+            CachedReplayGain("b", trackGain = null, trackPeak = null, albumGain = null, albumPeak = null),
+        )
+        coEvery { api.getReplayGain("b,c") } returns ReplayGainResponseWire(
+            items = mapOf("b" to ReplayGainWire(trackGain = -3f, trackPeak = 0.9f)),
+        )
+        val s = store()
+
+        s.load(listOf("a", "b", "c"))
+
+        assertEquals(-4f, s.get("a")?.albumGain)
+        assertEquals(-3f, s.get("b")?.trackGain)
+        assertNull(s.get("c"), "a track the server has not measured stays unknown")
+    }
+
+    @Test
+    fun `offline, the cache is all there is`() = runTest {
+        health = ServerHealth.Offline
+        coEvery { dao.replayGains(any()) } returns emptyList()
+        val s = store()
+
+        s.load(listOf("a"))
+
+        assertNull(s.get("a"))
+        coVerify(exactly = 0) { api.getReplayGain(any()) }
+    }
+
+    @Test
+    fun `a failed lookup leaves the track unknown, to be asked again`() = runTest {
+        coEvery { dao.replayGains(any()) } returns emptyList()
+        coEvery { api.getReplayGain(any()) } throws IOException("reset")
+        val s = store()
+
+        s.load(listOf("a"))
+
+        assertNull(s.get("a"))
+    }
+}

android/app/src/test/java/com/fabledsword/minstrel/player/output/SonosAlbumPlayTest.kt

@@ -0,0 +1,43 @@
+package com.fabledsword.minstrel.player.output
+
+import com.fabledsword.minstrel.models.TrackRef
+import org.junit.jupiter.api.Test
+import kotlin.test.assertEquals
+
+/**
+ * The Sonos queue plays straight through, so a track's album play is judged
+ * from its neighbours in the list sent (M464 #5002).
+ */
+class SonosAlbumPlayTest {
+
+    private fun t(album: String, n: Int?, disc: Int? = null) =
+        TrackRef(id = "$album-$disc-$n", title = "", albumId = album, artistId = "", trackNumber = n, discNumber = disc)
+
+    private fun asAlbum(queue: List<TrackRef>) = queue.indices.map { SonosQueueLoader.playingAsAlbum(queue, it) }
+
+    @Test
+    fun `an album in order plays as an album throughout`() {
+        assertEquals(listOf(true, true, true), asAlbum(listOf(t("a", 1), t("a", 2), t("a", 3))))
+    }
+
+    @Test
+    fun `a mix of albums plays as singles`() {
+        assertEquals(listOf(false, false, false), asAlbum(listOf(t("a", 1), t("b", 1), t("c", 4))))
+    }
+
+    @Test
+    fun `album order runs across discs`() {
+        assertEquals(listOf(true, true), asAlbum(listOf(t("a", 12, disc = 1), t("a", 1, disc = 2))))
+    }
+
+    @Test
+    fun `shuffled tracks of one album are not album play`() {
+        assertEquals(listOf(false, false), asAlbum(listOf(t("a", 3), t("a", 1))))
+    }
+
+    @Test
+    fun `unnumbered tracks and missing albums are never album play`() {
+        assertEquals(listOf(false, false), asAlbum(listOf(t("a", null), t("a", null))))
+        assertEquals(listOf(false, false), asAlbum(listOf(t("", 1), t("", 2))))
+    }
+}

android/app/src/test/java/com/fabledsword/minstrel/settings/data/NormalizationRepositoryTest.kt

@@ -0,0 +1,90 @@
+package com.fabledsword.minstrel.settings.data
+
+import com.fabledsword.minstrel.api.endpoints.MeApi
+import com.fabledsword.minstrel.auth.AuthStore
+import com.fabledsword.minstrel.cache.db.dao.CachedMutationDao
+import com.fabledsword.minstrel.cache.mutations.MutationKind
+import com.fabledsword.minstrel.cache.mutations.MutationQueue
+import io.mockk.coEvery
+import io.mockk.coVerify
+import io.mockk.every
+import io.mockk.mockk
+import io.mockk.verify
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.test.runTest
+import org.junit.jupiter.api.Test
+import retrofit2.Retrofit
+import java.io.IOException
+
+/**
+ * The normalization preference is written offline-first (rule 100): the
+ * device shows the change at once, and a change the server has not seen
+ * yet is never overwritten or reordered.
+ */
+class NormalizationRepositoryTest {
+    private val api: MeApi = mockk()
+    private val authStore: AuthStore = mockk(relaxed = true) {
+        every { normalization } returns MutableStateFlow(NormalizationPrefs.DEFAULT)
+    }
+    private val queue: MutationQueue = mockk(relaxed = true)
+    private val dao: CachedMutationDao = mockk()
+    private val retrofit: Retrofit = mockk {
+        every { create(MeApi::class.java) } returns api
+    }
+    private val repo = NormalizationRepository(retrofit, authStore, queue, dao)
+
+    private val album = NormalizationPrefs.DEFAULT.copy(mode = NormalizationMode.ALBUM)
+
+    @Test
+    fun `a change is shown at once and sent`() = runTest {
+        coEvery { dao.hasPending(MutationKind.NORMALIZATION_SET) } returns false
+        coEvery { api.putNormalization(album) } returns album
+
+        repo.set(album)
+
+        verify { authStore.setNormalization(album) }
+        coVerify { api.putNormalization(album) }
+        coVerify(exactly = 0) { queue.enqueueNormalizationSet(any()) }
+    }
+
+    @Test
+    fun `a change that cannot reach the server is queued`() = runTest {
+        coEvery { dao.hasPending(MutationKind.NORMALIZATION_SET) } returns false
+        coEvery { api.putNormalization(album) } throws IOException("offline")
+
+        repo.set(album)
+
+        verify { authStore.setNormalization(album) }
+        coVerify { queue.enqueueNormalizationSet(album) }
+    }
+
+    @Test
+    fun `a change behind a queued one queues too, so the older one cannot land last`() = runTest {
+        coEvery { dao.hasPending(MutationKind.NORMALIZATION_SET) } returns true
+
+        repo.set(album)
+
+        coVerify(exactly = 0) { api.putNormalization(any()) }
+        coVerify { queue.enqueueNormalizationSet(album) }
+    }
+
+    @Test
+    fun `refresh takes the server value`() = runTest {
+        coEvery { api.getNormalization() } returns album
+        coEvery { dao.hasPending(MutationKind.NORMALIZATION_SET) } returns false
+
+        repo.refresh()
+
+        verify { authStore.setNormalization(album) }
+    }
+
+    @Test
+    fun `refresh leaves a queued change on screen`() = runTest {
+        coEvery { api.getNormalization() } returns NormalizationPrefs.DEFAULT
+        coEvery { dao.hasPending(MutationKind.NORMALIZATION_SET) } returns true
+
+        repo.refresh()
+
+        verify(exactly = 0) { authStore.setNormalization(any()) }
+    }
+}

android/gradle/libs.versions.toml

@@ -21,7 +21,7 @@ kotlinx-serialization = "1.7.3"
 kotlinx-coroutines = "1.9.0"
 kotlinx-datetime = "0.6.1"
 kotlinx-serialization-converter = "1.0.0"
-media3 = "1.10.1"
+media3 = "1.11.0"
 mediarouter = "1.7.0"
 coil = "3.0.0-rc02"
 palette = "1.0.0"

ci-requirements.md

@@ -12,8 +12,9 @@ git.fabledsword.com/bvandeusen/ci-go:1.26
 git.fabledsword.com/bvandeusen/ci-android:36
 ```
 
-- `ci-go:1.26` — Go server tests (`.gitea/workflows/test-go.yml`), web SPA tests (`.gitea/workflows/test-web.yml`), and the release container build (`release.yml`'s `image-release` job).
-- `ci-android:36` — native Kotlin/Compose client: ktlint + detekt + unit tests + debug APK (`.gitea/workflows/android.yml`), and the signed release APK (`release.yml`'s `android-release` job).
+- `ci-go:1.26` — the `go`, `integration` and `web` lanes, `release-assets`, and the container build (`image-release`). All CI lives in one workflow, `.gitea/workflows/release.yml`, so every publishing job can depend on every lane (rule 177).
+- `golang:1.26-bookworm` (Docker Hub) — the `govulncheck` lane. Deliberately the same image as the Dockerfile's builder stage rather than `ci-go`, so the standard library it checks is the one in the shipped binary. Keep the two in step.
+- `ci-android:36` — native Kotlin/Compose client: ktlint + detekt + unit tests + debug APK (the `android` lane), and the signed release APK (`android-release`).
 
 **`ci-flutter` is no longer consumed, and `ci-flutter` can now be retired.**
 The M8 rewrite replaced the Flutter client with the native Android app and
@@ -30,9 +31,9 @@ split below. The label is a scheduling handle, not a toolchain assertion.
 
 ### From `ci-go:1.26`
 - **Go** (1.26 toolchain) — `go vet`, `go test -race`, `go build`, `go mod`.
-- **Node + npm** — `npm ci` and `npm test` / `npm run check` in `test-web.yml`.
-- **golangci-lint** — lint pass in `test-go.yml`.
-- **docker CLI** — bridge-IP discovery of the per-job Postgres service container in `test-go.yml` integration job (via the runner's shared `/var/run/docker.sock`).
+- **Node + npm** — `npm ci`, `npm audit`, `npm test` and `npm run check` in the `web` lane.
+- **golangci-lint** — lint pass in the `go` lane.
+- **docker CLI** — bridge-IP discovery of the per-job Postgres service container in the `integration` lane (via the runner's shared `/var/run/docker.sock`).
 - **docker buildx** — release container build + push in `release.yml`.
 - **curl** — release-asset polling / upload in `release.yml`.
 
@@ -45,7 +46,7 @@ split below. The label is a scheduling handle, not a toolchain assertion.
   No NDK: the native client has no C/C++ sources (this is why it isn't on
   `ci-flutter`).
 - **ktlint + detekt** — `./gradlew ktlintCheck` and `./gradlew detekt` in
-  `android.yml`. Image pins track `android/gradle/libs.versions.toml` so local
+  the `android` lane. Image pins track `android/gradle/libs.versions.toml` so local
   and CI checks agree.
 - **git** — `actions/checkout@v4` baseline (and any shell git operations).
 - **base64 + curl** — keystore decode + release-asset upload in `release.yml`'s
@@ -58,10 +59,10 @@ None.
 ## Notes
 
 - **Label/image split.** Workflows keep `runs-on: go-ci` / `runs-on: flutter-ci` as the scheduling label per the [`ci-runners.md`](https://…/FabledRulebook/ci-runners.md) "label = scheduling handle, image = `container.image`" pattern. The labels are intentional handles, not toolchain assertions — which is why the Android jobs still schedule on `flutter-ci` while pulling `ci-android:36`. Switch them to `android-ci` if that runner label is ever registered; nothing breaks either way.
-- **Integration-job docker-socket dependency.** `test-go.yml`'s integration job uses the runner's shared docker socket (`/var/run/docker.sock`) to bridge-IP-discover the per-job Postgres service container by name + network intersection — the dev compose's `minstrel-postgres-*` containers are explicitly skipped as belt-and-suspenders. Depends on `act_runner.valid_volumes` whitelisting the socket; if that ever stops auto-mounting, integration tests fail at the `docker inspect` step.
+- **Integration-job docker-socket dependency.** The `integration` lane uses the runner's shared docker socket (`/var/run/docker.sock`) to bridge-IP-discover the per-job Postgres service container by name + network intersection — the dev compose's `minstrel-postgres-*` containers are explicitly skipped as belt-and-suspenders. Depends on `act_runner.valid_volumes` whitelisting the socket; if that ever stops auto-mounting, integration tests fail at the `docker inspect` step.
 - **Go toolchain pin.** `go.mod` is on `go 1.25.0` because `golang.org/x/crypto v0.51.0` declares 1.25 as its minimum. `ci-go:1.26` satisfies this with headroom. Future `x/crypto` bumps that move the Go floor should be paired with an image-tag bump in this file + the workflows.
 - **In-app update channel — `needs:`, not polling.** `release.yml`'s `image-release` job declares `needs: [android-release]`, so on tag pushes the signed APK is guaranteed present before the image build starts — no polling window, no race. (The old cross-workflow polling against `flutter.yml` is gone with that workflow.) On non-tag `main` pushes `android-release` is skipped and `image-release` instead pulls the most recent release's APK and reconstructs its exact `versionName`, so `:latest` never ships without an update channel. It degrades to an empty `client/` — never a wrong version — if no release, asset, or tag commit-count can be resolved.
-- **Cache server reachability.** `test-web.yml` does NOT use `cache: 'npm'` on `actions/setup-node` — the Gitea Actions cache server isn't reachable from this runner's container network and `setup-node` was burning ~4m41s on ETIMEDOUT before failing open. With the migration to `ci-go:1.26`, `setup-node` is removed entirely (Node is in the image). The cache concern reappears if a future change re-introduces a network-dependent action.
+- **Cache server reachability.** The `web` lane does NOT use `cache: 'npm'` on `actions/setup-node` — the Gitea Actions cache server isn't reachable from this runner's container network and `setup-node` was burning ~4m41s on ETIMEDOUT before failing open. With the migration to `ci-go:1.26`, `setup-node` is removed entirely (Node is in the image). The cache concern reappears if a future change re-introduces a network-dependent action.
 - **Artifacts — stock `actions/upload-artifact@v7` and `actions/download-artifact@v8`; never `@v3`.**
   ```yaml
   uses: actions/upload-artifact@v7

cmd/minstrel/admin.go

@@ -55,12 +55,14 @@ func runAdmin(args []string) error {
 	}
 }
 
-// adminResetPassword resets a user's credentials. It updates BOTH
-// password_hash (bcrypt, for /api/auth/login) and subsonic_password
-// (plaintext, required for Subsonic t+s token verification) so neither
-// auth path is left stale. Recovers a locked-out operator when the
-// bootstrap password was missed or the DB volume was recreated (Fable
-// #321) without DB surgery.
+// adminResetPassword resets a user's login password (password_hash). It
+// recovers a locked-out operator when the bootstrap password was missed or
+// the DB volume was recreated (Fable #321) without DB surgery.
+//
+// It deliberately leaves subsonic_password alone. That column is stored in
+// plain text, and it used to receive the new login password here, so any
+// account recovered this way had its login password readable in the database
+// (#5026). The Subsonic password is generated separately in Settings.
 func adminResetPassword(args []string) error {
 	fs := flag.NewFlagSet("admin reset-password", flag.ContinueOnError)
 	configPath := fs.String("config", os.Getenv("MINSTREL_CONFIG"), "path to YAML config file")
@@ -112,13 +114,6 @@ func adminResetPassword(args []string) error {
 	}); err != nil {
 		return fmt.Errorf("update password_hash: %w", err)
 	}
-	sp := pw
-	if err := q.SetSubsonicPassword(ctx, dbq.SetSubsonicPasswordParams{
-		ID:               user.ID,
-		SubsonicPassword: &sp,
-	}); err != nil {
-		return fmt.Errorf("update subsonic_password: %w", err)
-	}
 
 	if generated {
 		fmt.Printf("minstrel: password for %q reset.\nNew password: %s\n", *username, pw)

cmd/minstrel/main.go

@@ -14,6 +14,7 @@ import (
 
 	"github.com/jackc/pgx/v5/pgxpool"
 
+	"git.fabledsword.com/bvandeusen/minstrel/internal/acoustid"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/config"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/coplay"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/coverart"
@@ -122,7 +123,31 @@ func run() error {
 	}
 	defer pool.Close()
 
-	scanner := library.New(pool, logger, cfg.Library.ScanPaths)
+	// Fingerprinting settings (M400 #3913): one instance, shared by the scanner,
+	// the fingerprint backfill, the duplicate sweep and the admin API, so a save
+	// reaches all of them without a restart. A load failure is logged, not fatal:
+	// the service falls back to the shipped defaults.
+	fpSettings, fpErr := library.NewFingerprintSettingsService(ctx, pool)
+	if fpErr != nil {
+		logger.Warn("fingerprint settings: using defaults", "err", fpErr)
+	}
+	scanner := library.New(pool, logger, cfg.Library.ScanPaths, fpSettings)
+
+	// Loudness analysis settings (M464 #4995): shared by the loudness backfill
+	// and the admin API, and falls back to the defaults like the above.
+	loudSettings, loudErr := library.NewLoudnessSettingsService(ctx, pool)
+	if loudErr != nil {
+		logger.Warn("loudness settings: using defaults", "err", loudErr)
+	}
+
+	// AcoustID lookup settings (M401): shared by the lookup worker and the
+	// admin API. A load failure leaves the lookup off.
+	acoustIDSettings, acoustIDErr := library.NewAcoustIDSettingsService(ctx, pool)
+	if acoustIDErr != nil {
+		logger.Warn("acoustid settings: using defaults (lookup off)", "err", acoustIDErr)
+	}
+	acoustIDLookup := library.NewAcoustIDLookupWorker(pool, logger.With("component", "acoustid_lookup"),
+		acoustIDSettings, acoustid.New(acoustid.DefaultBaseURL))
 
 	contact := cfg.Library.ContactEmail
 	if contact == "" {
@@ -214,6 +239,27 @@ func run() error {
 	// SQL, no external calls; empty on single-user servers.
 	go coplay.NewWorker(pool, logger.With("component", "coplay")).Run(ctx)
 
+	// Fingerprint backfill (M400 #3908): fingerprints the tracks the scan never
+	// will — everything imported before fingerprinting existed, and rows derived
+	// by an older method. A worker of its own rather than a scan stage; see
+	// internal/library/fingerprint_backfill.go for why.
+	go library.NewFingerprintBackfillWorker(pool, logger.With("component", "fingerprint_backfill"), fpSettings).Run(ctx)
+
+	// Loudness backfill (M464 #4995): measures every track's loudness for
+	// normalization, new tracks included; the scan only drops a changed file's
+	// measurement. See internal/library/loudness_backfill.go.
+	go library.NewLoudnessBackfillWorker(pool, logger.With("component", "loudness_backfill"), loudSettings).Run(ctx)
+
+	// AcoustID lookup (M401): fills the recording MBIDs untagged tracks lack,
+	// so the similarity arms can see them. Idle until the operator adds a key
+	// and switches it on. See internal/library/acoustid_lookup.go.
+	go acoustIDLookup.Run(ctx)
+
+	// Duplicate sweep (M400 #3910): proposes groups of tracks holding one
+	// recording, from the fingerprints above. Sweeps only when fingerprints have
+	// changed since the last sweep.
+	go library.NewDuplicateSweepWorker(pool, logger.With("component", "duplicate_sweep"), fpSettings).Run(ctx)
+
 	// Start the tag-enrichment worker (#1490). Reconciles the compiled-in
 	// tag providers with tag_provider_settings, bumps the sources version if
 	// the provider set changed (re-opening settled rows), then drains tracks
@@ -357,11 +403,22 @@ func run() error {
 	srv.PlaylistScheduler = playlistScheduler
 	srv.RecSettings = recSettings
 	srv.TagSettings = tagSettings
+	srv.FingerprintSettings = fpSettings
+	srv.LoudnessSettings = loudSettings
+	srv.AcoustIDLookup = acoustIDLookup
+	// The sweeper above holds this same instance, so a save from the admin
+	// card changes what it does on its next tick (#3936).
+	srv.ReacqSettings = reacqSettings
 	srv.StreamSecret = cfg.StreamSecret
 	httpServer := &http.Server{
 		Addr:              cfg.Server.Address,
 		Handler:           srv.Router(),
 		ReadHeaderTimeout: 10 * time.Second,
+		// Closes keep-alive connections nobody is using. Deliberately no
+		// ReadTimeout or WriteTimeout: either would cut off audio streams and
+		// the SSE event stream. Request bodies get their own deadline in the
+		// server's limitRequestBody middleware instead.
+		IdleTimeout: 120 * time.Second,
 	}
 
 	errCh := make(chan error, 1)

docker-compose.yml

@@ -8,7 +8,7 @@ version: "3.9"
 # tests at it:
 #   make test-integration
 # (CI runs the same suite against its own ephemeral Postgres service —
-# see .gitea/workflows/test-go.yml.)
+# see the `integration` job in .gitea/workflows/release.yml.)
 #
 # Full stack (server + db):
 #   docker compose up --build

docs/hosting.md

@@ -0,0 +1,92 @@
+# Hosting Minstrel
+
+Minstrel serves plain HTTP on port 4533 and never terminates TLS itself. On a
+home network or a VPN you trust, that is all you need. Once the server is
+reachable from the internet, put it behind a reverse proxy that speaks HTTPS,
+and tell Minstrel about that proxy. This page covers both.
+
+## On a LAN or VPN
+
+Publish the port to the network and use `http://<host>:4533`:
+
+```yaml
+    ports: ['4533:4533']
+```
+
+If nothing sits in front of Minstrel, set **Admin → Integrations → Client IP
+detection** to 0. It defaults to 1, which assumes one proxy (see below for
+why that matters).
+
+## On the internet
+
+Three things, all required:
+
+1. **Don't publish 4533 to the world.** Bind it to the loopback interface so
+   only the proxy on the same host can reach it:
+
+   ```yaml
+       ports: ['127.0.0.1:4533:4533']
+   ```
+
+   If the proxy runs in another container on the same Docker network, drop
+   `ports:` entirely and point the proxy at `minstrel:4533`.
+
+2. **Terminate HTTPS at a reverse proxy.** Any proxy works. With Caddy, which
+   gets and renews certificates by itself:
+
+   ```
+   music.example.com {
+       reverse_proxy 127.0.0.1:4533
+   }
+   ```
+
+   Two settings matter for every proxy:
+   - **Don't buffer responses.** Live updates use Server-Sent Events and audio
+     is streamed; a buffering proxy holds both back. Caddy streams by default.
+     For nginx, set `proxy_buffering off;`.
+   - **Allow long-lived responses.** An event stream stays open for as long as
+     the app is. Raise the proxy's read timeout well past a minute (nginx:
+     `proxy_read_timeout 1h;`).
+
+3. **Tell Minstrel where it lives**, in **Admin → Integrations**:
+   - **Client IP detection:** the number of proxies in front of Minstrel. One
+     proxy (Caddy, Traefik, nginx) is 1; Cloudflare in front of Traefik is 2.
+     Minstrel uses this to find the real client address, for login rate
+     limits and the sessions list, and to tell whether a request arrived over
+     HTTPS.
+   - **Public address:** the URL people use, e.g. `https://music.example.com`.
+     Password-reset emails link here. **Until it is set, no reset email is
+     sent**, so a forged `Host` header can never put a reset token on a link
+     to someone else's server.
+
+### Why the proxy count matters
+
+Minstrel only believes `X-Forwarded-For` and `X-Forwarded-Proto` from the
+number of proxies you configure, counted from the right. Set it too high, or
+leave it at the default of 1 with no proxy in front, and a client can write
+those headers itself: it could claim any address to slip past the per-address
+login limit, or claim HTTPS. With no proxy, set it to 0.
+
+When the proxy reports HTTPS, Minstrel marks the session cookie `Secure` and
+sends `Strict-Transport-Security`. Over plain HTTP it does neither, and it
+never redirects to HTTPS, so LAN use keeps working unchanged.
+
+## First account
+
+A fresh server with no accounts prints a **setup token** in its log:
+
+```
+docker compose logs minstrel | grep setup_token
+```
+
+Creating the first account (which becomes the admin) requires that token, so
+whoever reaches a newly exposed server first can't claim it. The token
+changes on every restart until an account exists.
+
+## Android app
+
+The app connects over whatever URL you give it, HTTP or HTTPS. Once the
+server has a public HTTPS address, give the app that address so the session
+cookie never crosses the internet unencrypted. See
+[security notes](./security.md#android-allows-plain-http) for why plain HTTP
+is still allowed.

docs/security.md

@@ -0,0 +1,105 @@
+# Security notes
+
+What Minstrel does to protect accounts, and the reasoning behind the
+decisions that look odd at first. For deployment steps, see
+[hosting](./hosting.md).
+
+## Accounts and sessions
+
+- **Passwords** are stored as bcrypt hashes.
+- **Login, registration and password reset are rate-limited:** 10 failed
+  sign-ins per account and 50 per address per 15 minutes, with similar limits
+  on register, forgot-password and reset. The Subsonic `/rest` API shares the
+  login limits. An unknown username takes as long to reject as a wrong
+  password, so timing doesn't reveal which accounts exist.
+- **Sessions** are random 256-bit tokens; the server stores only their
+  SHA-256. A session ends after 30 days unused or 365 days in total. Changing
+  your password signs out your other devices; a password reset, or an admin
+  resetting it, signs out all of them.
+- **API keys** (the OpenSubsonic `apiKey`) are stored as SHA-256 too, so a
+  key is shown once, when you generate it in Settings, and can only be
+  replaced after that.
+- **The first account** on an empty server needs the setup token from the
+  server log (see [hosting](./hosting.md#first-account)).
+- **Password-reset links** are built only from the configured public address,
+  never from the request's `Host` header.
+
+## Requests
+
+- Request bodies are capped at 4 MiB and must arrive within 30 seconds.
+  Streams and the live-event connection are unaffected.
+- Every response carries `X-Content-Type-Options: nosniff`,
+  `Referrer-Policy: strict-origin-when-cross-origin`, a restrictive
+  `Permissions-Policy` and `X-Frame-Options: DENY`. The web app also gets a
+  `Content-Security-Policy` that allows only its own scripts, by hash.
+- Media responses are `Cache-Control: private`, so a shared cache never keeps
+  one user's audio or artwork for another.
+
+## CSRF: SameSite cookies plus JSON-only writes
+
+There are no CSRF tokens. The session cookie is `SameSite=Strict`, so
+browsers don't send it with requests that start on another site. That leaves
+one gap: SameSite treats every subdomain of the same registrable domain as the
+same site, so a different app on `other.example.com` could still send a
+request carrying the cookie. To close it, any state-changing `/api` request
+authenticated by the cookie must have a JSON body (`Content-Type:
+application/json`) or no body at all. An HTML form or a script on another
+origin can't send JSON without a CORS preflight, and Minstrel answers no
+cross-origin preflight. Requests authenticated with a bearer token or the
+Subsonic query parameters carry nothing a browser attaches on its own, so
+they aren't checked.
+
+## Subsonic sign-in, and the one password stored in plain text
+
+Classic Subsonic clients sign in with `t` and `s`: the MD5 of the password
+followed by a random salt. To check that, the server has to know the password
+itself, so supporting this sign-in method means storing a password Minstrel
+can read. That is the Subsonic password, and it is the only credential
+Minstrel keeps unhashed.
+
+- **The recommended way in is the API key.** Clients that support the
+  OpenSubsonic `apiKey` should use it. The key is stored hashed and can be
+  replaced at any time in Settings.
+- **The Subsonic password is never your login password.** Minstrel generates
+  it (**Settings → Subsonic password**), shows it once, and lets you replace
+  or turn it off. Because it is random, a copy of the database exposes access
+  to this server's Subsonic API and nothing else: it can't be a password you
+  also use somewhere else.
+- **`t`/`s` and `p=` sign-in are off for an account until it has a Subsonic
+  password.** Plain `p=` sign-in is additionally off server-wide unless
+  `subsonic.allow_plaintext_password` is enabled.
+- `minstrel admin reset-password` changes only the login password. Older
+  versions also copied it into the Subsonic password; upgrading clears every
+  Subsonic password once, so those copies are gone. An account that used
+  `t`/`s` sign-in needs a new Subsonic password generated in Settings.
+
+## Android allows plain HTTP
+
+The Android app permits cleartext connections, for two reasons that can't be
+narrowed to a list of hosts. The server address is whatever the user types,
+and many self-hosted servers run plain HTTP on a LAN. And UPnP, DLNA and
+Sonos speakers are controlled over plain HTTP at addresses that are only
+known once they're discovered. The reasoning lives in
+`android/app/src/main/res/xml/network_security_config.xml`.
+
+This doesn't weaken app updates: an APK altered in transit fails the
+platform's signature check. It does mean a server reached over plain HTTP
+across the internet exposes the session cookie in transit, which is why the
+[hosting guide](./hosting.md) puts public servers behind HTTPS.
+
+On the phone, the session cookie is encrypted with a key held in the Android
+Keystore, so a copy of the app's files doesn't yield a usable session.
+
+## Build pipeline
+
+Nothing is published unless every check passes: the Go, integration, web and
+Android test suites, `govulncheck` against the toolchain that builds the
+image, and `npm audit` on the packages that ship to the browser. See
+`.gitea/workflows/release.yml`.
+
+## Reporting a problem
+
+Open an issue on the
+[repository](https://git.fabledsword.com/bvandeusen/minstrel/issues), or
+contact the maintainer privately first if it's something that shouldn't be
+public until fixed.

go.mod

@@ -13,6 +13,7 @@ require (
 	github.com/jackc/pgx/v5 v5.9.2
 	github.com/stretchr/testify v1.11.1
 	golang.org/x/crypto v0.51.0
+	golang.org/x/sync v0.21.0
 	gopkg.in/yaml.v3 v3.0.1
 )
 
@@ -25,7 +26,6 @@ require (
 	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 // indirect
 	github.com/robfig/cron/v3 v3.0.1 // indirect
 	github.com/rogpeppe/go-internal v1.14.1 // indirect
-	golang.org/x/sync v0.20.0 // indirect
 	golang.org/x/sys v0.44.0 // indirect
-	golang.org/x/text v0.37.0 // indirect
+	golang.org/x/text v0.39.0 // indirect
 )

go.sum

@@ -95,12 +95,12 @@ go.uber.org/goleak v1.3.0 h1:2K3zAYmnTNqV73imy9J1T3WC+gmCePx2hEGkimedGto=
 go.uber.org/goleak v1.3.0/go.mod h1:CoHD4mav9JJNrW/WLlf7HGZPjdw8EucARQHekz1X6bE=
 golang.org/x/crypto v0.51.0 h1:IBPXwPfKxY7cWQZ38ZCIRPI50YLeevDLlLnyC5wRGTI=
 golang.org/x/crypto v0.51.0/go.mod h1:8AdwkbraGNABw2kOX6YFPs3WM22XqI4EXEd8g+x7Oc8=
-golang.org/x/sync v0.20.0 h1:e0PTpb7pjO8GAtTs2dQ6jYa5BWYlMuX047Dco/pItO4=
-golang.org/x/sync v0.20.0/go.mod h1:9xrNwdLfx4jkKbNva9FpL6vEN7evnE43NNNJQ2LF3+0=
+golang.org/x/sync v0.21.0 h1:HLII4xRRTtCRkxYp4HNFF0Js/Og6q2i++KXbg0gHCwM=
+golang.org/x/sync v0.21.0/go.mod h1:9xrNwdLfx4jkKbNva9FpL6vEN7evnE43NNNJQ2LF3+0=
 golang.org/x/sys v0.44.0 h1:ildZl3J4uzeKP07r2F++Op7E9B29JRUy+a27EibtBTQ=
 golang.org/x/sys v0.44.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
-golang.org/x/text v0.37.0 h1:Cqjiwd9eSg8e0QAkyCaQTNHFIIzWtidPahFWR83rTrc=
-golang.org/x/text v0.37.0/go.mod h1:a5sjxXGs9hsn/AJVwuElvCAo9v8QYLzvavO5z2PiM38=
+golang.org/x/text v0.39.0 h1:UbZz4pLOvn600D6Oh6GGEI6VAmndrEBLv8/6BEXzyus=
+golang.org/x/text v0.39.0/go.mod h1:3UwRclnC2g0TU9x8PZiyfOajCd1zaUNHF9cvqcQZ+ZM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c h1:Hei/4ADfdWqJk1ZMxUNpqntNwaWcugrBjAiHlqqRiVk=
 gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c/go.mod h1:JHkPIbrfpd72SG/EVd6muEfDQjcINNoR0C8j2r3qZ4Q=

internal/acoustid/client.go

@@ -0,0 +1,267 @@
+// Package acoustid looks up MusicBrainz recording ids by acoustic fingerprint
+// through the AcoustID web service (M401).
+//
+// What it relies on, from https://acoustid.org/webservice (read 2026-10-06):
+//   - POST https://api.acoustid.org/v2/lookup with client, duration (whole
+//     seconds), fingerprint (fpcalc's compressed string) and meta. A gzip body
+//     with Content-Encoding: gzip is accepted and preferred, because
+//     fingerprints are long.
+//   - meta=recordings returns each recording's title, duration and artists,
+//     which the worker needs to tell several candidates apart (M401 D5).
+//   - "Do not make more than 3 requests per second."
+//   - The service is free for non-commercial use only.
+//
+// Error codes are the server's own, from acoustid-server's
+// acoustid/api/errors.py.
+package acoustid
+
+import (
+	"bytes"
+	"cmp"
+	"compress/gzip"
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"slices"
+	"strconv"
+	"sync"
+	"time"
+)
+
+// DefaultBaseURL is the lookup endpoint.
+const DefaultBaseURL = "https://api.acoustid.org/v2/lookup"
+
+const (
+	// minInterval keeps to AcoustID's 3 requests a second with headroom: one
+	// every 400ms is 2.5 a second.
+	minInterval = 400 * time.Millisecond
+	// lookupTimeout bounds one request, connection included (rule 156). A
+	// lookup answers in well under a second; 20s is the line past which slow
+	// has become never.
+	lookupTimeout = 20 * time.Second
+	// bodyLimit caps the response read. A lookup with meta=recordings for a
+	// popular song runs to tens of kilobytes.
+	bodyLimit = 2 << 20
+	userAgent = "Minstrel ( https://git.fabledsword.com/bvandeusen/minstrel )"
+)
+
+// The server's error codes that the worker treats differently.
+const (
+	codeInvalidFingerprint = 3
+	codeInvalidAPIKey      = 4
+	codeServiceUnavailable = 13
+	codeTooManyRequests    = 14
+	codeUnknownApplication = 17
+)
+
+var (
+	// ErrInvalidKey: the operator's application key was refused. No lookup
+	// can succeed until it is changed, so the worker stops and says so.
+	ErrInvalidKey = errors.New("acoustid: the API key was refused")
+	// ErrInvalidFingerprint: AcoustID rejected this track's fingerprint. A
+	// verdict on the track, not on the service.
+	ErrInvalidFingerprint = errors.New("acoustid: the fingerprint was rejected")
+	// ErrUnavailable: the service could not answer now (unreachable, timed
+	// out, overloaded or rate limiting). Says nothing about the track, so the
+	// lookup is tried again later.
+	ErrUnavailable = errors.New("acoustid: the service is unavailable")
+)
+
+// Recording is one MusicBrainz recording a fingerprint matched.
+type Recording struct {
+	ID    string
+	Title string
+	// DurationSec is MusicBrainz's length for the recording; 0 when unknown.
+	DurationSec int
+	Artists     []string
+}
+
+// Candidate is a recording with the score of the best AcoustID result that
+// linked to it.
+type Candidate struct {
+	Recording
+	Score float64
+}
+
+// Client calls the lookup endpoint, at most one request per minInterval.
+type Client struct {
+	baseURL string
+	http    *http.Client
+
+	mu       sync.Mutex
+	lastCall time.Time
+}
+
+// New returns a client for baseURL (DefaultBaseURL in production).
+func New(baseURL string) *Client {
+	return &Client{baseURL: baseURL, http: &http.Client{Timeout: lookupTimeout}}
+}
+
+// Lookup asks which recordings match fingerprint, a compressed chromaprint
+// of audio durationSec long. It returns every candidate, best score first;
+// choosing among them is the caller's job. No match is an empty slice and
+// no error.
+func (c *Client) Lookup(ctx context.Context, apiKey, fingerprint string, durationSec int) ([]Candidate, error) {
+	if err := c.wait(ctx); err != nil {
+		return nil, err
+	}
+	body, err := gzipForm(url.Values{
+		"client":      {apiKey},
+		"duration":    {strconv.Itoa(durationSec)},
+		"fingerprint": {fingerprint},
+		"meta":        {"recordings"},
+		"format":      {"json"},
+	})
+	if err != nil {
+		return nil, err
+	}
+	reqCtx, cancel := context.WithTimeout(ctx, lookupTimeout)
+	defer cancel()
+	req, err := http.NewRequestWithContext(reqCtx, http.MethodPost, c.baseURL, bytes.NewReader(body))
+	if err != nil {
+		return nil, fmt.Errorf("acoustid: build request: %w", err)
+	}
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	req.Header.Set("Content-Encoding", "gzip")
+	req.Header.Set("Accept", "application/json")
+	req.Header.Set("User-Agent", userAgent)
+
+	resp, err := c.http.Do(req)
+	if err != nil {
+		// The caller giving up is not the service failing.
+		if ctx.Err() != nil {
+			return nil, ctx.Err()
+		}
+		return nil, fmt.Errorf("%w: %v", ErrUnavailable, err)
+	}
+	defer func() { _ = resp.Body.Close() }()
+	raw, err := io.ReadAll(io.LimitReader(resp.Body, bodyLimit))
+	if err != nil {
+		return nil, fmt.Errorf("%w: read body: %v", ErrUnavailable, err)
+	}
+	return parseLookup(resp.StatusCode, raw)
+}
+
+// wait blocks until minInterval has passed since the last request, then
+// claims the slot.
+func (c *Client) wait(ctx context.Context) error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if d := time.Until(c.lastCall.Add(minInterval)); d > 0 {
+		t := time.NewTimer(d)
+		defer t.Stop()
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+		case <-t.C:
+		}
+	}
+	c.lastCall = time.Now()
+	return nil
+}
+
+func gzipForm(v url.Values) ([]byte, error) {
+	var buf bytes.Buffer
+	zw := gzip.NewWriter(&buf)
+	if _, err := zw.Write([]byte(v.Encode())); err != nil {
+		return nil, fmt.Errorf("acoustid: compress request: %w", err)
+	}
+	if err := zw.Close(); err != nil {
+		return nil, fmt.Errorf("acoustid: compress request: %w", err)
+	}
+	return buf.Bytes(), nil
+}
+
+type lookupResponse struct {
+	Status string `json:"status"`
+	Error  *struct {
+		Code    int    `json:"code"`
+		Message string `json:"message"`
+	} `json:"error"`
+	Results []struct {
+		ID         string  `json:"id"`
+		Score      float64 `json:"score"`
+		Recordings []struct {
+			ID       string  `json:"id"`
+			Title    string  `json:"title"`
+			Duration float64 `json:"duration"`
+			Artists  []struct {
+				Name string `json:"name"`
+			} `json:"artists"`
+		} `json:"recordings"`
+	} `json:"results"`
+}
+
+// parseLookup reads a lookup response. AcoustID reports its errors in the
+// body with a code, alongside a 4xx or 5xx status, so the body is read first
+// and the status only decides when the body says nothing usable.
+func parseLookup(status int, raw []byte) ([]Candidate, error) {
+	var r lookupResponse
+	if err := json.Unmarshal(raw, &r); err != nil {
+		if status != http.StatusOK {
+			return nil, fmt.Errorf("%w: status %d", ErrUnavailable, status)
+		}
+		return nil, fmt.Errorf("%w: unreadable response: %v", ErrUnavailable, err)
+	}
+	if r.Status != "ok" {
+		return nil, lookupError(status, r)
+	}
+	return candidates(r), nil
+}
+
+func lookupError(status int, r lookupResponse) error {
+	if r.Error == nil {
+		return fmt.Errorf("%w: status %d", ErrUnavailable, status)
+	}
+	switch r.Error.Code {
+	case codeInvalidAPIKey, codeUnknownApplication:
+		return fmt.Errorf("%w: %s", ErrInvalidKey, r.Error.Message)
+	case codeInvalidFingerprint:
+		return fmt.Errorf("%w: %s", ErrInvalidFingerprint, r.Error.Message)
+	case codeServiceUnavailable, codeTooManyRequests:
+		return fmt.Errorf("%w: %s", ErrUnavailable, r.Error.Message)
+	}
+	if status >= http.StatusInternalServerError {
+		return fmt.Errorf("%w: %s", ErrUnavailable, r.Error.Message)
+	}
+	// Any other code is a request this client built wrongly. Retrying would
+	// repeat it, so it is named rather than folded into unavailable.
+	return fmt.Errorf("acoustid: error %d: %s", r.Error.Code, r.Error.Message)
+}
+
+// candidates flattens the results into one entry per recording. The same
+// recording can hang off several AcoustID results (one audio, fingerprinted
+// from different sources); it keeps the best score it was seen with.
+// Results with no linked recording are fingerprints AcoustID knows but nobody
+// has tied to MusicBrainz, and carry nothing to fill.
+func candidates(r lookupResponse) []Candidate {
+	out := []Candidate{}
+	at := map[string]int{}
+	for _, res := range r.Results {
+		for _, rec := range res.Recordings {
+			if rec.ID == "" {
+				continue
+			}
+			if i, ok := at[rec.ID]; ok {
+				out[i].Score = max(out[i].Score, res.Score)
+				continue
+			}
+			c := Candidate{
+				Recording: Recording{ID: rec.ID, Title: rec.Title, DurationSec: int(rec.Duration + 0.5)},
+				Score:     res.Score,
+			}
+			for _, a := range rec.Artists {
+				c.Artists = append(c.Artists, a.Name)
+			}
+			at[rec.ID] = len(out)
+			out = append(out, c)
+		}
+	}
+	// Best first, keeping AcoustID's order among equals.
+	slices.SortStableFunc(out, func(a, b Candidate) int { return cmp.Compare(b.Score, a.Score) })
+	return out
+}

internal/acoustid/client_test.go

@@ -0,0 +1,220 @@
+package acoustid
+
+import (
+	"compress/gzip"
+	"context"
+	"errors"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"strings"
+	"testing"
+	"time"
+)
+
+// docSample is the meta=recordings response printed in AcoustID's own
+// documentation (https://acoustid.org/webservice), artists and release groups
+// as given.
+const docSample = `{
+  "status": "ok",
+  "results": [{
+    "score": 1.0,
+    "id": "9ff43b6a-4f16-427c-93c2-92307ca505e0",
+    "recordings": [{
+      "duration": 639,
+      "releasegroups": [{"type": "Album", "id": "ddaa2d4d-314e-3e7c-b1d0-f6d207f5aa2f", "title": "Before the Dawn Heals Us"}],
+      "title": "Lower Your Eyelids to Die With the Sun",
+      "id": "cd2e7c47-16f5-46c6-a37c-a1eb7bf599ff",
+      "artists": [{"id": "6d7b7cd4-254b-4c25-83f6-dd20f98ceacd", "name": "M83"}]
+    }]
+  }]
+}`
+
+// severalSample is the shape the worker has to disambiguate: one audio linked
+// to two recordings (an album and a single release), the album recording
+// reached again through a weaker second result, and a third result that
+// AcoustID knows but nobody has tied to MusicBrainz.
+const severalSample = `{
+  "status": "ok",
+  "results": [
+    {"score": 0.71, "id": "a2", "recordings": [{"id": "rec-album", "title": "Song", "duration": 200.4}]},
+    {"score": 0.93, "id": "a1", "recordings": [
+      {"id": "rec-album", "title": "Song", "duration": 200.4, "artists": [{"name": "A"}, {"name": "B"}]},
+      {"id": "rec-single", "title": "Song (radio edit)", "duration": 181}
+    ]},
+    {"score": 0.88, "id": "a3"}
+  ]
+}`
+
+func TestParseLookup(t *testing.T) {
+	cases := []struct {
+		name string
+		body string
+		want []Candidate
+	}{
+		{"single match", docSample, []Candidate{{
+			Recording: Recording{
+				ID: "cd2e7c47-16f5-46c6-a37c-a1eb7bf599ff", Title: "Lower Your Eyelids to Die With the Sun",
+				DurationSec: 639, Artists: []string{"M83"},
+			},
+			Score: 1.0,
+		}}},
+		{"several recordings", severalSample, []Candidate{
+			{Recording: Recording{ID: "rec-album", Title: "Song", DurationSec: 200}, Score: 0.93},
+			{Recording: Recording{ID: "rec-single", Title: "Song (radio edit)", DurationSec: 181}, Score: 0.93},
+		}},
+		// Choosing a threshold is the worker's; the parser carries the score.
+		{"below threshold", `{"status":"ok","results":[{"score":0.31,"id":"x","recordings":[{"id":"rec"}]}]}`,
+			[]Candidate{{Recording: Recording{ID: "rec"}, Score: 0.31}}},
+		{"no results", `{"status":"ok","results":[]}`, []Candidate{}},
+		{"results with no recordings", `{"status":"ok","results":[{"score":0.99,"id":"x"}]}`, []Candidate{}},
+	}
+	for _, c := range cases {
+		got, err := parseLookup(http.StatusOK, []byte(c.body))
+		if err != nil {
+			t.Errorf("%s: err = %v", c.name, err)
+			continue
+		}
+		if !sameCandidates(got, c.want) {
+			t.Errorf("%s:\n got %+v\nwant %+v", c.name, got, c.want)
+		}
+	}
+}
+
+// The first result's recording is the album one with both artists; the
+// weaker repeat must not replace its fields, only fail to lower its score.
+func TestParseLookup_RepeatedRecordingKeepsBestScoreAndFirstFields(t *testing.T) {
+	got, err := parseLookup(http.StatusOK, []byte(severalSample))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got[0].ID != "rec-album" || got[0].Score != 0.93 {
+		t.Errorf("album recording = %+v, want score 0.93", got[0])
+	}
+}
+
+func TestParseLookup_Errors(t *testing.T) {
+	cases := []struct {
+		name   string
+		status int
+		body   string
+		want   error
+	}{
+		{"invalid key", 400, `{"status":"error","error":{"code":4,"message":"invalid API key"}}`, ErrInvalidKey},
+		{"unknown application", 400, `{"status":"error","error":{"code":17,"message":"unknown application"}}`, ErrInvalidKey},
+		{"bad fingerprint", 400, `{"status":"error","error":{"code":3,"message":"invalid fingerprint"}}`, ErrInvalidFingerprint},
+		{"rate limited", 429, `{"status":"error","error":{"code":14,"message":"rate limit (3.000000 requests per second) exceeded, try again later"}}`, ErrUnavailable},
+		{"down", 503, `{"status":"error","error":{"code":13,"message":"service currently unavailable, try again later"}}`, ErrUnavailable},
+		{"internal error", 500, `{"status":"error","error":{"code":5,"message":"internal error"}}`, ErrUnavailable},
+		{"proxy page", 502, `<html>Bad Gateway</html>`, ErrUnavailable},
+	}
+	for _, c := range cases {
+		_, err := parseLookup(c.status, []byte(c.body))
+		if !errors.Is(err, c.want) {
+			t.Errorf("%s: err = %v, want %v", c.name, err, c.want)
+		}
+	}
+
+	// A code this client caused (here a missing parameter) is neither the
+	// key nor the service, so it must not read as either: retrying repeats it.
+	_, err := parseLookup(400, []byte(`{"status":"error","error":{"code":2,"message":"missing required parameter \"fingerprint\""}}`))
+	if err == nil || errors.Is(err, ErrUnavailable) || errors.Is(err, ErrInvalidKey) || !strings.Contains(err.Error(), "missing required parameter") {
+		t.Errorf("missing parameter: err = %v", err)
+	}
+}
+
+// The request is what AcoustID documents: a gzip form POST carrying the key,
+// whole-second duration, fingerprint and meta=recordings.
+func TestLookup_SendsACompressedForm(t *testing.T) {
+	var form url.Values
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodPost || r.Header.Get("Content-Encoding") != "gzip" {
+			t.Errorf("request %s with Content-Encoding %q, want a gzip POST", r.Method, r.Header.Get("Content-Encoding"))
+		}
+		zr, err := gzip.NewReader(r.Body)
+		if err != nil {
+			t.Fatalf("body is not gzip: %v", err)
+		}
+		raw, _ := io.ReadAll(zr)
+		form, _ = url.ParseQuery(string(raw))
+		_, _ = io.WriteString(w, docSample)
+	}))
+	defer srv.Close()
+
+	got, err := New(srv.URL).Lookup(context.Background(), "key123", "AQADtE", 241)
+	if err != nil || len(got) != 1 {
+		t.Fatalf("Lookup = %+v, %v", got, err)
+	}
+	for k, want := range map[string]string{
+		"client": "key123", "duration": "241", "fingerprint": "AQADtE", "meta": "recordings", "format": "json",
+	} {
+		if form.Get(k) != want {
+			t.Errorf("form %s = %q, want %q", k, form.Get(k), want)
+		}
+	}
+}
+
+func TestLookup_DeadlineIsUnavailable(t *testing.T) {
+	release := make(chan struct{})
+	srv := httptest.NewServer(http.HandlerFunc(func(http.ResponseWriter, *http.Request) { <-release }))
+	defer srv.Close()
+	defer close(release)
+
+	c := New(srv.URL)
+	c.http.Timeout = 50 * time.Millisecond
+	_, err := c.Lookup(context.Background(), "k", "f", 1)
+	if !errors.Is(err, ErrUnavailable) {
+		t.Errorf("err = %v, want ErrUnavailable", err)
+	}
+}
+
+// A cancelled caller is reported as such, never as the service being down.
+func TestLookup_CancelledCallerIsNotUnavailable(t *testing.T) {
+	release := make(chan struct{})
+	srv := httptest.NewServer(http.HandlerFunc(func(http.ResponseWriter, *http.Request) { <-release }))
+	defer srv.Close()
+	defer close(release)
+
+	ctx, cancel := context.WithTimeout(context.Background(), 50*time.Millisecond)
+	defer cancel()
+	_, err := New(srv.URL).Lookup(ctx, "k", "f", 1)
+	if !errors.Is(err, context.DeadlineExceeded) || errors.Is(err, ErrUnavailable) {
+		t.Errorf("err = %v, want the caller's own deadline", err)
+	}
+}
+
+func TestLookup_KeepsToTheRateLimit(t *testing.T) {
+	var at []time.Time
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		at = append(at, time.Now())
+		_, _ = io.WriteString(w, `{"status":"ok","results":[]}`)
+	}))
+	defer srv.Close()
+
+	c := New(srv.URL)
+	for range 3 {
+		if _, err := c.Lookup(context.Background(), "k", "f", 1); err != nil {
+			t.Fatal(err)
+		}
+	}
+	for i := 1; i < len(at); i++ {
+		// A little slack for the server's own clock reading.
+		if gap := at[i].Sub(at[i-1]); gap < minInterval-10*time.Millisecond {
+			t.Errorf("requests %d and %d were %s apart, want at least %s", i-1, i, gap, minInterval)
+		}
+	}
+}
+
+func sameCandidates(a, b []Candidate) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i := range a {
+		if a[i].ID != b[i].ID || a[i].Title != b[i].Title || a[i].DurationSec != b[i].DurationSec ||
+			a[i].Score != b[i].Score || strings.Join(a[i].Artists, "|") != strings.Join(b[i].Artists, "|") {
+			return false
+		}
+	}
+	return true
+}

internal/api/admin_acoustid.go

@@ -0,0 +1,171 @@
+package api
+
+import (
+	"encoding/json"
+	"errors"
+	"net/http"
+	"time"
+
+	"git.fabledsword.com/bvandeusen/minstrel/internal/apierror"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/library"
+)
+
+// AcoustID recording-id lookup, admin side (M401 #3922).
+
+// acoustIDUnsettledLimit caps the admin list of tracks a lookup could not
+// settle. It is a list to read, not to page through.
+const acoustIDUnsettledLimit = 200
+
+// acoustIDSettingsResp never carries the key, only whether one is stored.
+type acoustIDSettingsResp struct {
+	Enabled   bool    `json:"enabled"`
+	MinScore  float32 `json:"min_score"`
+	APIKeySet bool    `json:"api_key_set"`
+}
+
+func acoustIDSettingsRespOf(s library.AcoustIDSettings) acoustIDSettingsResp {
+	return acoustIDSettingsResp{Enabled: s.Enabled, MinScore: s.MinScore, APIKeySet: s.APIKey != ""}
+}
+
+type acoustIDStatusResp struct {
+	Running    bool       `json:"running"`
+	LastPassAt *time.Time `json:"last_pass_at"`
+	// Problem is why the last pass stopped short, in words for the card.
+	Problem string `json:"problem"`
+}
+
+// acoustIDCoverageResp: from_tag + from_acoustid + the tracks with no MBID =
+// total. ambiguous, no_match and failed are lookup states of tracks with no
+// MBID; pending is what the worker still has to look at.
+type acoustIDCoverageResp struct {
+	Total        int64 `json:"total"`
+	FromTag      int64 `json:"from_tag"`
+	FromAcoustID int64 `json:"from_acoustid"`
+	Ambiguous    int64 `json:"ambiguous"`
+	NoMatch      int64 `json:"no_match"`
+	Failed       int64 `json:"failed"`
+	Pending      int64 `json:"pending"`
+}
+
+type acoustIDResp struct {
+	Settings acoustIDSettingsResp `json:"settings"`
+	// Ready is whether the worker will call AcoustID at all: switched on
+	// and holding a key.
+	Ready    bool                 `json:"ready"`
+	Status   acoustIDStatusResp   `json:"status"`
+	Coverage acoustIDCoverageResp `json:"coverage"`
+}
+
+// handleGetAcoustID implements GET /api/admin/library/acoustid: the settings,
+// what the worker is doing, and how much of the library has an MBID by source.
+func (h *handlers) handleGetAcoustID(w http.ResponseWriter, r *http.Request) {
+	row, err := library.AcoustIDCoverage(r.Context(), h.pool)
+	if err != nil {
+		writeErrWithLog(w, h.logger, "admin: get acoustid coverage", apierror.InternalMsg("lookup failed", err))
+		return
+	}
+	cfg := h.acoustIDLookup.Settings().Get()
+	st := h.acoustIDLookup.Status()
+	resp := acoustIDResp{
+		Settings: acoustIDSettingsRespOf(cfg),
+		Ready:    cfg.Ready(),
+		Status:   acoustIDStatusResp{Running: st.Running, Problem: st.Problem},
+		Coverage: acoustIDCoverageResp{
+			Total:        row.Total,
+			FromTag:      row.FromTag,
+			FromAcoustID: row.FromAcoustid,
+			Ambiguous:    row.Ambiguous,
+			NoMatch:      row.NoMatch,
+			Failed:       row.Failed,
+			Pending:      row.Pending,
+		},
+	}
+	if !st.LastPassAt.IsZero() {
+		at := st.LastPassAt.UTC()
+		resp.Status.LastPassAt = &at
+	}
+	writeJSON(w, http.StatusOK, resp)
+}
+
+// acoustIDSettingsReq is the PUT body. api_key left out keeps the stored key;
+// an empty string clears it.
+type acoustIDSettingsReq struct {
+	Enabled  bool    `json:"enabled"`
+	MinScore float32 `json:"min_score"`
+	APIKey   *string `json:"api_key"`
+}
+
+// handleUpdateAcoustIDSettings implements PUT /api/admin/library/acoustid-settings.
+func (h *handlers) handleUpdateAcoustIDSettings(w http.ResponseWriter, r *http.Request) {
+	var req acoustIDSettingsReq
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeErr(w, apierror.BadRequest("invalid_body", "malformed JSON"))
+		return
+	}
+	saved, err := h.acoustIDLookup.Settings().Set(r.Context(), library.AcoustIDSettingsUpdate{
+		Enabled: req.Enabled, MinScore: req.MinScore, APIKey: req.APIKey,
+	})
+	if err != nil {
+		if errors.Is(err, library.ErrAcoustIDSettingOutOfRange) {
+			writeErr(w, apierror.BadRequest("invalid_setting", err.Error()))
+			return
+		}
+		writeErrWithLog(w, h.logger, "admin acoustid settings: update failed", apierror.Internal(err))
+		return
+	}
+	writeJSON(w, http.StatusOK, acoustIDSettingsRespOf(saved))
+}
+
+// handleRunAcoustIDLookup implements POST /api/admin/library/acoustid/run:
+// start a pass now rather than at the next tick. 409 when the lookup is off
+// or has no key, so the card can say so rather than appear to do nothing.
+func (h *handlers) handleRunAcoustIDLookup(w http.ResponseWriter, _ *http.Request) {
+	if !h.acoustIDLookup.Settings().Get().Ready() {
+		writeErr(w, apierror.Conflict("not_ready",
+			"Switch the AcoustID lookup on and add an API key first."))
+		return
+	}
+	h.acoustIDLookup.Kick()
+	w.WriteHeader(http.StatusAccepted)
+}
+
+type acoustIDUnsettledResp struct {
+	TrackID    string    `json:"track_id"`
+	Title      string    `json:"title"`
+	Artist     string    `json:"artist"`
+	Album      string    `json:"album"`
+	FilePath   string    `json:"file_path"`
+	State      string    `json:"state"`
+	BestScore  *float32  `json:"best_score"`
+	Candidates int32     `json:"candidates"`
+	Detail     *string   `json:"detail"`
+	LookedUpAt time.Time `json:"looked_up_at"`
+}
+
+// handleListUnsettledAcoustID implements GET /api/admin/library/acoustid/unsettled:
+// the tracks a lookup could not settle (ambiguous or failed), so they can be
+// found and tagged by hand.
+func (h *handlers) handleListUnsettledAcoustID(w http.ResponseWriter, r *http.Request) {
+	rows, err := dbq.New(h.pool).ListUnsettledAcoustIDLookups(r.Context(), acoustIDUnsettledLimit)
+	if err != nil {
+		writeErrWithLog(w, h.logger, "admin: list unsettled acoustid lookups", apierror.InternalMsg("lookup failed", err))
+		return
+	}
+	out := make([]acoustIDUnsettledResp, 0, len(rows))
+	for _, row := range rows {
+		out = append(out, acoustIDUnsettledResp{
+			TrackID:    uuidToString(row.ID),
+			Title:      row.Title,
+			Artist:     row.ArtistName,
+			Album:      row.AlbumTitle,
+			FilePath:   row.FilePath,
+			State:      row.State,
+			BestScore:  row.BestScore,
+			Candidates: row.Candidates,
+			Detail:     row.Detail,
+			LookedUpAt: row.LookedUpAt.Time.UTC(),
+		})
+	}
+	writeJSON(w, http.StatusOK, out)
+}

internal/api/admin_coverage.go

@@ -1,10 +1,12 @@
 package api
 
 import (
+	"context"
 	"net/http"
 
 	"git.fabledsword.com/bvandeusen/minstrel/internal/apierror"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/library"
 )
 
 // coverageRollupResp is the wire shape for GET /api/admin/library/coverage.
@@ -36,3 +38,46 @@ func (h *handlers) handleGetLibraryCoverage(w http.ResponseWriter, r *http.Reque
 		PendingNoMbid: row.PendingNoMbid,
 	})
 }
+
+// fingerprintCoverageResp is the wire shape for GET /api/admin/library/fingerprints.
+// fingerprinted + rejected + pending = total. Missing tracks are not counted:
+// there is no file to fingerprint. Enabled travels with the counts because with
+// fingerprinting off (#3913) pending never shrinks, and a gauge that implies
+// progress would be promising work nothing is doing.
+type fingerprintCoverageResp struct {
+	Total         int64 `json:"total"`
+	Fingerprinted int64 `json:"fingerprinted"`
+	Rejected      int64 `json:"rejected"`
+	Pending       int64 `json:"pending"`
+	Enabled       bool  `json:"enabled"`
+}
+
+// fingerprintCoverage reads the gauge against the current settings: a print at
+// another length counts as pending, because the backfill will re-derive it.
+func (h *handlers) fingerprintCoverage(ctx context.Context) (fingerprintCoverageResp, error) {
+	cfg := h.fingerprintSettings.Get()
+	row, err := library.FingerprintCoverage(ctx, h.pool, cfg)
+	if err != nil {
+		return fingerprintCoverageResp{}, err
+	}
+	return fingerprintCoverageResp{
+		Total:         row.Total,
+		Fingerprinted: row.Fingerprinted,
+		Rejected:      row.Rejected,
+		Pending:       row.Pending,
+		Enabled:       cfg.Enabled,
+	}, nil
+}
+
+// handleGetFingerprintCoverage implements GET /api/admin/library/fingerprints:
+// how far the fingerprint backfill (#3908) has got. The backfill is its own
+// worker spanning many passes, with no scan run to attach a tally to, so its
+// progress is read live here. Always 200; zeros on an empty library.
+func (h *handlers) handleGetFingerprintCoverage(w http.ResponseWriter, r *http.Request) {
+	cov, err := h.fingerprintCoverage(r.Context())
+	if err != nil {
+		writeErrWithLog(w, h.logger, "admin: get fingerprint coverage", apierror.InternalMsg("lookup failed", err))
+		return
+	}
+	writeJSON(w, http.StatusOK, cov)
+}

internal/api/admin_duplicates.go

@@ -0,0 +1,316 @@
+package api
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"io"
+	"net/http"
+
+	"github.com/go-chi/chi/v5"
+	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgtype"
+
+	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/library"
+)
+
+// duplicateMemberView is one copy in a proposed duplicate group. LikeCount and
+// PlayCount span every user: the report is admin-only, and what a copy carries
+// is the fact the operator weighs when choosing which to keep.
+type duplicateMemberView struct {
+	TrackID     string `json:"track_id"`
+	Title       string `json:"title"`
+	ArtistName  string `json:"artist_name"`
+	AlbumID     string `json:"album_id"`
+	AlbumTitle  string `json:"album_title"`
+	FilePath    string `json:"file_path"`
+	FileFormat  string `json:"file_format"`
+	FileSize    int64  `json:"file_size"`
+	DurationSec int32  `json:"duration_sec"`
+	AddedAt     string `json:"added_at"`
+	LikeCount   int64  `json:"like_count"`
+	PlayCount   int64  `json:"play_count"`
+}
+
+// duplicateGroupView is one proposal. SurvivorTrackID and SurvivorReason are
+// the copy the report proposes keeping and the rule that chose it
+// (library.ProposeSurvivor) — a default the merge (#3911) lets the operator
+// override.
+type duplicateGroupView struct {
+	ID                string                `json:"id"`
+	Tier              string                `json:"tier"`
+	WorstBitErrorRate *float32              `json:"worst_bit_error_rate"`
+	DetectedAt        string                `json:"detected_at"`
+	SurvivorTrackID   string                `json:"survivor_track_id"`
+	SurvivorReason    string                `json:"survivor_reason"`
+	Members           []duplicateMemberView `json:"members"`
+}
+
+// duplicateSweepView is the latest sweep. State is "never" when none has run,
+// which is what lets the page tell an empty report apart from a sweep that
+// found nothing.
+type duplicateSweepView struct {
+	State            string  `json:"state"`
+	StartedAt        *string `json:"started_at"`
+	FinishedAt       *string `json:"finished_at"`
+	Candidates       *int32  `json:"candidates"`
+	GroupsFound      *int32  `json:"groups_found"`
+	OversizeClusters *int32  `json:"oversize_clusters"`
+	ErrorMessage     *string `json:"error_message"`
+}
+
+// adminDuplicatesResponse is the paged report. Total counts groups.
+type adminDuplicatesResponse struct {
+	Sweep        duplicateSweepView      `json:"sweep"`
+	Fingerprints fingerprintCoverageResp `json:"fingerprints"`
+	Total        int64                   `json:"total"`
+	Limit        int                     `json:"limit"`
+	Offset       int                     `json:"offset"`
+	Groups       []duplicateGroupView    `json:"groups"`
+}
+
+// handleListDuplicates implements GET /api/admin/library/duplicates (#3912).
+//
+// Read-only. The sweep's state and the fingerprint backfill's progress travel
+// with the groups because an empty report means three different things — still
+// fingerprinting, never swept, or swept and clean — and the page has to say which.
+func (h *handlers) handleListDuplicates(w http.ResponseWriter, r *http.Request) {
+	limit, offset, err := parsePaging(r.URL.Query())
+	if err != nil {
+		writeAdminJSONErr(w, http.StatusBadRequest, "invalid_paging")
+		return
+	}
+	ctx := r.Context()
+	q := dbq.New(h.pool)
+
+	sweep := duplicateSweepView{State: "never"}
+	last, err := q.GetLatestDuplicateSweep(ctx)
+	switch {
+	case err == nil:
+		sweep = duplicateSweepViewOf(last)
+	case !errors.Is(err, pgx.ErrNoRows):
+		h.logger.Error("admin: latest duplicate sweep", "err", err)
+		writeAdminJSONErr(w, http.StatusInternalServerError, "server_error")
+		return
+	}
+
+	cov, err := h.fingerprintCoverage(ctx)
+	if err != nil {
+		h.logger.Error("admin: fingerprint coverage", "err", err)
+		writeAdminJSONErr(w, http.StatusInternalServerError, "server_error")
+		return
+	}
+	total, err := q.CountPendingDuplicateGroups(ctx)
+	if err != nil {
+		h.logger.Error("admin: count duplicate groups", "err", err)
+		writeAdminJSONErr(w, http.StatusInternalServerError, "server_error")
+		return
+	}
+	rows, err := q.ListPendingDuplicateGroupMembers(ctx, dbq.ListPendingDuplicateGroupMembersParams{
+		PageLimit: int32(limit), PageOffset: int32(offset),
+	})
+	if err != nil {
+		h.logger.Error("admin: list duplicate groups", "err", err)
+		writeAdminJSONErr(w, http.StatusInternalServerError, "server_error")
+		return
+	}
+
+	writeJSON(w, http.StatusOK, adminDuplicatesResponse{
+		Sweep:        sweep,
+		Fingerprints: cov,
+		Total:        total,
+		Limit:        limit,
+		Offset:       offset,
+		Groups:       foldDuplicateGroups(rows),
+	})
+}
+
+func duplicateSweepViewOf(s dbq.DuplicateSweep) duplicateSweepView {
+	v := duplicateSweepView{
+		State:            "running",
+		Candidates:       s.Candidates,
+		GroupsFound:      s.GroupsFound,
+		OversizeClusters: s.OversizeClusters,
+		ErrorMessage:     s.ErrorMessage,
+	}
+	started := formatTimestamp(s.StartedAt)
+	v.StartedAt = &started
+	if s.FinishedAt.Valid {
+		finished := formatTimestamp(s.FinishedAt)
+		v.FinishedAt = &finished
+		v.State = "finished"
+	}
+	return v
+}
+
+// foldDuplicateGroups folds the one-row-per-member query result into groups and
+// proposes each group's survivor. It relies on the query ordering members of a
+// group together, so a run-length fold is enough and the page order holds.
+func foldDuplicateGroups(rows []dbq.ListPendingDuplicateGroupMembersRow) []duplicateGroupView {
+	groups := make([]duplicateGroupView, 0, 8)
+	var candidates [][]library.SurvivorCandidate
+	for _, row := range rows {
+		id := uuidToString(row.GroupID)
+		if n := len(groups); n == 0 || groups[n-1].ID != id {
+			groups = append(groups, duplicateGroupView{
+				ID:                id,
+				Tier:              row.Tier,
+				WorstBitErrorRate: row.WorstBitErrorRate,
+				DetectedAt:        formatTimestamp(row.DetectedAt),
+			})
+			candidates = append(candidates, nil)
+		}
+		n := len(groups) - 1
+		trackID := uuidToString(row.TrackID)
+		groups[n].Members = append(groups[n].Members, duplicateMemberView{
+			TrackID:     trackID,
+			Title:       row.Title,
+			ArtistName:  row.ArtistName,
+			AlbumID:     uuidToString(row.AlbumID),
+			AlbumTitle:  row.AlbumTitle,
+			FilePath:    row.FilePath,
+			FileFormat:  row.FileFormat,
+			FileSize:    row.FileSize,
+			DurationSec: row.DurationMs / 1000,
+			AddedAt:     formatTimestamp(row.AddedAt),
+			LikeCount:   row.LikeCount,
+			PlayCount:   row.PlayCount,
+		})
+		candidates[n] = append(candidates[n], library.SurvivorCandidate{
+			TrackID: trackID, FileFormat: row.FileFormat, FileSize: row.FileSize, AddedAt: row.AddedAt.Time,
+		})
+	}
+	for i := range groups {
+		groups[i].SurvivorTrackID, groups[i].SurvivorReason = library.ProposeSurvivor(candidates[i])
+	}
+	return groups
+}
+
+// handleRunDuplicateSweep implements POST /api/admin/library/duplicates/sweep:
+// 202 when a sweep starts, 409 sweep_in_progress when one is already running.
+// The sweep outlives the request, so it runs on a background context, as
+// handleTriggerScan's scan does.
+func (h *handlers) handleRunDuplicateSweep(w http.ResponseWriter, _ *http.Request) {
+	// Runs whatever the sweep interval says: the interval paces the automatic
+	// sweep, and an operator pressing the button has already decided.
+	started, err := library.TryStartDuplicateSweep(
+		context.Background(), h.pool, h.logger.With("source", "manual"), h.fingerprintSettings.Get(),
+	)
+	if err != nil {
+		h.logger.Error("admin: start duplicate sweep", "err", err)
+		writeAdminJSONErr(w, http.StatusInternalServerError, "server_error")
+		return
+	}
+	if !started {
+		writeAdminJSONErr(w, http.StatusConflict, "sweep_in_progress")
+		return
+	}
+	writeJSON(w, http.StatusAccepted, map[string]bool{"started": true})
+}
+
+// handleDismissDuplicateGroup implements POST
+// /api/admin/library/duplicates/{id}/dismiss: "these are not duplicates". The
+// sweep keeps the dismissal and will not propose that set of tracks again. 404
+// duplicate_group_not_pending when the group was already resolved or is gone.
+func (h *handlers) handleDismissDuplicateGroup(w http.ResponseWriter, r *http.Request) {
+	id, ok := parseUUID(chi.URLParam(r, "id"))
+	if !ok {
+		writeAdminJSONErr(w, http.StatusBadRequest, "invalid_id")
+		return
+	}
+	n, err := dbq.New(h.pool).DismissDuplicateGroup(r.Context(), id)
+	if err != nil {
+		h.logger.Error("admin: dismiss duplicate group", "err", err)
+		writeAdminJSONErr(w, http.StatusInternalServerError, "server_error")
+		return
+	}
+	if n == 0 {
+		writeAdminJSONErr(w, http.StatusNotFound, "duplicate_group_not_pending")
+		return
+	}
+	writeJSON(w, http.StatusOK, map[string]string{"status": "dismissed"})
+}
+
+// mergeDuplicateRequest chooses the copy to keep. An empty survivor_track_id
+// keeps the report's proposal.
+type mergeDuplicateRequest struct {
+	SurvivorTrackID string `json:"survivor_track_id"`
+	Unmonitor       bool   `json:"unmonitor"`
+}
+
+// mergeDuplicateResponse reports what the merge removed. RemovedPaths are files
+// deleted from disk; the operator reads them to know exactly what went.
+type mergeDuplicateResponse struct {
+	SurvivorTrackID       string   `json:"survivor_track_id"`
+	RemovedPaths          []string `json:"removed_paths"`
+	LidarrUnmonitorFailed *bool    `json:"lidarr_unmonitor_failed,omitempty"`
+}
+
+// mergeRequestBodyLimit bounds the request body. It holds one id and a flag.
+const mergeRequestBodyLimit = 1 << 16
+
+// handleMergeDuplicateGroup implements POST /api/admin/library/duplicates/{id}/merge
+// (#3911): keep one copy, move the others' likes, plays and playlist entries onto
+// it, and delete the others' files and rows.
+//
+// Errors:
+//   - 409 library_not_writable / 500 file_delete_failed when a file could not be
+//     removed — nothing was changed (fileRemoveAPIError)
+//   - 404 duplicate_group_not_pending when the group was already resolved
+//   - 400 survivor_not_in_group, invalid_id, invalid_body
+func (h *handlers) handleMergeDuplicateGroup(w http.ResponseWriter, r *http.Request) {
+	admin, ok := requireUser(w, r)
+	if !ok {
+		return
+	}
+	groupID, ok := parseUUID(chi.URLParam(r, "id"))
+	if !ok {
+		writeAdminJSONErr(w, http.StatusBadRequest, "invalid_id")
+		return
+	}
+	var body mergeDuplicateRequest
+	if err := json.NewDecoder(http.MaxBytesReader(w, r.Body, mergeRequestBodyLimit)).Decode(&body); err != nil && !errors.Is(err, io.EOF) {
+		writeAdminJSONErr(w, http.StatusBadRequest, "invalid_body")
+		return
+	}
+	var survivorID pgtype.UUID // invalid: keep the proposal
+	if body.SurvivorTrackID != "" {
+		if survivorID, ok = parseUUID(body.SurvivorTrackID); !ok {
+			writeAdminJSONErr(w, http.StatusBadRequest, "invalid_id")
+			return
+		}
+	}
+
+	res, unmonitorFailed, err := h.tracks.MergeDuplicates(r.Context(), groupID, survivorID, admin.ID, body.Unmonitor)
+	if err != nil {
+		if apiErr, ok := fileRemoveAPIError(err); ok {
+			logFileRemoveFailure(h.logger, apiErr, "group_id", uuidToString(groupID))
+			writeErr(w, apiErr)
+			return
+		}
+		switch {
+		case errors.Is(err, library.ErrDuplicateGroupNotPending):
+			writeAdminJSONErr(w, http.StatusNotFound, "duplicate_group_not_pending")
+		case errors.Is(err, library.ErrSurvivorNotInGroup):
+			writeAdminJSONErr(w, http.StatusBadRequest, "survivor_not_in_group")
+		default:
+			h.logger.Error("admin: merge duplicate group", "group_id", uuidToString(groupID), "err", err)
+			writeAdminJSONErr(w, http.StatusInternalServerError, "server_error")
+		}
+		return
+	}
+
+	resp := mergeDuplicateResponse{
+		SurvivorTrackID: uuidToString(res.Survivor.TrackID),
+		RemovedPaths:    make([]string, 0, len(res.Removed)),
+	}
+	for _, c := range res.Removed {
+		resp.RemovedPaths = append(resp.RemovedPaths, c.FilePath)
+	}
+	if body.Unmonitor && unmonitorFailed {
+		failed := true
+		resp.LidarrUnmonitorFailed = &failed
+	}
+	writeJSON(w, http.StatusOK, resp)
+}

internal/api/admin_duplicates_test.go

@@ -0,0 +1,65 @@
+package api
+
+import (
+	"testing"
+	"time"
+
+	"github.com/jackc/pgx/v5/pgtype"
+
+	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
+)
+
+func dupUUID(b byte) pgtype.UUID {
+	var u pgtype.UUID
+	u.Bytes[15] = b
+	u.Valid = true
+	return u
+}
+
+func dupTS(t time.Time) pgtype.Timestamptz { return pgtype.Timestamptz{Time: t, Valid: true} }
+
+// Rows arrive one per member, members of a group together. The fold must keep
+// groups apart, keep the query's order, and propose each group's survivor from
+// its own members only.
+func TestFoldDuplicateGroups(t *testing.T) {
+	older := time.Date(2025, 1, 1, 0, 0, 0, 0, time.UTC)
+	newer := older.Add(48 * time.Hour)
+	ber := float32(0.04)
+	rows := []dbq.ListPendingDuplicateGroupMembersRow{
+		// Group 1: identical audio, sizes tie, the older copy should be kept.
+		{GroupID: dupUUID(1), Tier: "exact", DetectedAt: dupTS(newer), TrackID: dupUUID(10),
+			Title: "WWW", FileFormat: "mp3", FileSize: 6_900_000, DurationMs: 215_400, AddedAt: dupTS(newer), PlayCount: 3},
+		{GroupID: dupUUID(1), Tier: "exact", DetectedAt: dupTS(newer), TrackID: dupUUID(11),
+			Title: "WWW", FileFormat: "mp3", FileSize: 6_900_000, DurationMs: 215_400, AddedAt: dupTS(older), LikeCount: 1},
+		// Group 2: the same recording, FLAC against MP3.
+		{GroupID: dupUUID(2), Tier: "acoustic", WorstBitErrorRate: &ber, DetectedAt: dupTS(older), TrackID: dupUUID(20),
+			Title: "Lovesick", FileFormat: "mp3", FileSize: 9_000_000, DurationMs: 198_000, AddedAt: dupTS(older)},
+		{GroupID: dupUUID(2), Tier: "acoustic", WorstBitErrorRate: &ber, DetectedAt: dupTS(older), TrackID: dupUUID(21),
+			Title: "Lovesick", FileFormat: "flac", FileSize: 30_000_000, DurationMs: 198_000, AddedAt: dupTS(newer)},
+	}
+
+	got := foldDuplicateGroups(rows)
+	if len(got) != 2 {
+		t.Fatalf("folded %d groups, want 2", len(got))
+	}
+
+	g1, g2 := got[0], got[1]
+	if g1.ID != uuidToString(dupUUID(1)) || len(g1.Members) != 2 || g1.WorstBitErrorRate != nil {
+		t.Fatalf("group 1 = %+v, want the exact pair with no score", g1)
+	}
+	if g1.SurvivorTrackID != uuidToString(dupUUID(11)) || g1.SurvivorReason != "in the library longest" {
+		t.Errorf("group 1 survivor = (%s, %q), want the older copy", g1.SurvivorTrackID, g1.SurvivorReason)
+	}
+	if g1.Members[0].DurationSec != 215 || g1.Members[0].PlayCount != 3 || g1.Members[1].LikeCount != 1 {
+		t.Errorf("group 1 members lost their facts: %+v", g1.Members)
+	}
+
+	if g2.Tier != "acoustic" || g2.WorstBitErrorRate == nil || *g2.WorstBitErrorRate != ber {
+		t.Fatalf("group 2 = %+v, want the acoustic pair with its score", g2)
+	}
+	// Chosen from group 2's own members: a survivor leaking across groups is
+	// exactly what a wrong fold boundary would produce.
+	if g2.SurvivorTrackID != uuidToString(dupUUID(21)) || g2.SurvivorReason != "lossless (flac)" {
+		t.Errorf("group 2 survivor = (%s, %q), want the FLAC copy", g2.SurvivorTrackID, g2.SurvivorReason)
+	}
+}

internal/api/admin_fingerprint_settings.go

@@ -0,0 +1,67 @@
+package api
+
+import (
+	"encoding/json"
+	"errors"
+	"net/http"
+
+	"git.fabledsword.com/bvandeusen/minstrel/internal/apierror"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/library"
+)
+
+// fingerprintSettingsBody is the wire shape for GET and PUT
+// /api/admin/library/fingerprint-settings (M400 #3913). The threshold travels as
+// the bit-error rate the matcher uses; the card presents it as a match percentage.
+type fingerprintSettingsBody struct {
+	Enabled                 bool    `json:"enabled"`
+	ChromaprintLengthSec    int32   `json:"chromaprint_length_sec"`
+	AcousticMaxBitErrorRate float64 `json:"acoustic_max_bit_error_rate"`
+	BackfillConcurrency     int32   `json:"backfill_concurrency"`
+	SweepIntervalHours      int32   `json:"sweep_interval_hours"`
+}
+
+func fingerprintSettingsBodyOf(s library.FingerprintSettings) fingerprintSettingsBody {
+	return fingerprintSettingsBody{
+		Enabled:                 s.Enabled,
+		ChromaprintLengthSec:    s.ChromaprintLengthSec,
+		AcousticMaxBitErrorRate: s.AcousticMaxBitErrorRate,
+		BackfillConcurrency:     s.BackfillConcurrency,
+		SweepIntervalHours:      s.SweepIntervalHours,
+	}
+}
+
+// handleGetFingerprintSettings implements GET /api/admin/library/fingerprint-settings.
+func (h *handlers) handleGetFingerprintSettings(w http.ResponseWriter, _ *http.Request) {
+	writeJSON(w, http.StatusOK, fingerprintSettingsBodyOf(h.fingerprintSettings.Get()))
+}
+
+// handleUpdateFingerprintSettings implements PUT /api/admin/library/fingerprint-settings.
+//
+// A whole-row write. A body that leaves a field out decodes it as zero, which no
+// field accepts, so a partial save is refused rather than zeroing what it omitted.
+// The saved settings reach the scanner and both workers at once: they share the
+// service instance.
+func (h *handlers) handleUpdateFingerprintSettings(w http.ResponseWriter, r *http.Request) {
+	var req fingerprintSettingsBody
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeErr(w, apierror.BadRequest("invalid_body", "malformed JSON"))
+		return
+	}
+	saved, err := h.fingerprintSettings.Set(r.Context(), library.FingerprintSettings{
+		Enabled:                 req.Enabled,
+		ChromaprintLengthSec:    req.ChromaprintLengthSec,
+		AcousticMaxBitErrorRate: req.AcousticMaxBitErrorRate,
+		BackfillConcurrency:     req.BackfillConcurrency,
+		SweepIntervalHours:      req.SweepIntervalHours,
+	})
+	if err != nil {
+		// Validation mirrors migration 0061's CHECKs and names the field.
+		if errors.Is(err, library.ErrFingerprintSettingOutOfRange) {
+			writeErr(w, apierror.BadRequest("invalid_setting", err.Error()))
+			return
+		}
+		writeErrWithLog(w, h.logger, "admin fingerprint settings: update failed", apierror.Internal(err))
+		return
+	}
+	writeJSON(w, http.StatusOK, fingerprintSettingsBodyOf(saved))
+}

internal/api/admin_fingerprint_settings_test.go

@@ -0,0 +1,55 @@
+package api
+
+import (
+	"encoding/json"
+	"io"
+	"log/slog"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"git.fabledsword.com/bvandeusen/minstrel/internal/library"
+)
+
+func TestGetFingerprintSettings_ServesDefaultsWithoutAService(t *testing.T) {
+	h := &handlers{logger: slog.New(slog.NewTextHandler(io.Discard, nil))}
+	rec := httptest.NewRecorder()
+	h.handleGetFingerprintSettings(rec, httptest.NewRequest(http.MethodGet, "/api/admin/library/fingerprint-settings", nil))
+	if rec.Code != http.StatusOK {
+		t.Fatalf("status = %d, want 200", rec.Code)
+	}
+	var got fingerprintSettingsBody
+	if err := json.NewDecoder(rec.Body).Decode(&got); err != nil {
+		t.Fatalf("decode: %v", err)
+	}
+	if want := fingerprintSettingsBodyOf(library.DefaultFingerprintSettings); got != want {
+		t.Fatalf("body = %+v, want the defaults %+v", got, want)
+	}
+}
+
+func TestUpdateFingerprintSettings_Rejects(t *testing.T) {
+	h := &handlers{logger: slog.New(slog.NewTextHandler(io.Discard, nil))}
+	for name, tc := range map[string]struct {
+		body     string
+		code     string
+		mentions string
+	}{
+		"a value out of range, naming the field": {
+			body:     `{"enabled":true,"chromaprint_length_sec":5,"acoustic_max_bit_error_rate":0.15,"backfill_concurrency":2,"sweep_interval_hours":1}`,
+			code:     "invalid_setting",
+			mentions: "chromaprint_length_sec",
+		},
+		// A partial body would otherwise zero every field it left out.
+		"a body missing fields": {body: `{"enabled":false}`, code: "invalid_setting"},
+		"malformed JSON":        {body: `{"enabled":`, code: "invalid_body"},
+	} {
+		rec := httptest.NewRecorder()
+		h.handleUpdateFingerprintSettings(rec, httptest.NewRequest(
+			http.MethodPut, "/api/admin/library/fingerprint-settings", strings.NewReader(tc.body)))
+		body := rec.Body.String()
+		if rec.Code != http.StatusBadRequest || !strings.Contains(body, `"`+tc.code+`"`) || !strings.Contains(body, tc.mentions) {
+			t.Errorf("%s: status %d body %s; want 400 %s mentioning %q", name, rec.Code, body, tc.code, tc.mentions)
+		}
+	}
+}

internal/api/admin_loudness.go

@@ -0,0 +1,88 @@
+package api
+
+import (
+	"encoding/json"
+	"errors"
+	"net/http"
+
+	"git.fabledsword.com/bvandeusen/minstrel/internal/apierror"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/library"
+)
+
+// loudnessCoverageResp is the wire shape for GET /api/admin/library/loudness
+// (M464 #4995). measured + silent + unreadable + pending = total; missing
+// tracks are not counted. Enabled travels with the counts because with
+// analysis off, pending never shrinks, and a gauge implying progress would be
+// promising work nothing is doing.
+type loudnessCoverageResp struct {
+	Total      int64 `json:"total"`
+	Measured   int64 `json:"measured"`
+	Silent     int64 `json:"silent"`
+	Unreadable int64 `json:"unreadable"`
+	Pending    int64 `json:"pending"`
+	Enabled    bool  `json:"enabled"`
+}
+
+// handleGetLoudnessCoverage implements GET /api/admin/library/loudness: how
+// far the loudness backfill has got. Always 200; zeros on an empty library.
+func (h *handlers) handleGetLoudnessCoverage(w http.ResponseWriter, r *http.Request) {
+	row, err := library.LoudnessCoverage(r.Context(), h.pool)
+	if err != nil {
+		writeErrWithLog(w, h.logger, "admin: get loudness coverage", apierror.InternalMsg("lookup failed", err))
+		return
+	}
+	writeJSON(w, http.StatusOK, loudnessCoverageResp{
+		Total:      row.Total,
+		Measured:   row.Measured,
+		Silent:     row.Silent,
+		Unreadable: row.Unreadable,
+		Pending:    row.Pending,
+		Enabled:    h.loudnessSettings.Get().Enabled,
+	})
+}
+
+// loudnessSettingsBody is the wire shape for GET and PUT
+// /api/admin/library/loudness-settings.
+type loudnessSettingsBody struct {
+	Enabled             bool  `json:"enabled"`
+	BackfillConcurrency int32 `json:"backfill_concurrency"`
+	LeveledCacheMB      int32 `json:"leveled_cache_mb"`
+}
+
+func loudnessSettingsBodyOf(s library.LoudnessSettings) loudnessSettingsBody {
+	return loudnessSettingsBody{
+		Enabled:             s.Enabled,
+		BackfillConcurrency: s.BackfillConcurrency,
+		LeveledCacheMB:      s.LeveledCacheMB,
+	}
+}
+
+// handleGetLoudnessSettings implements GET /api/admin/library/loudness-settings.
+func (h *handlers) handleGetLoudnessSettings(w http.ResponseWriter, _ *http.Request) {
+	writeJSON(w, http.StatusOK, loudnessSettingsBodyOf(h.loudnessSettings.Get()))
+}
+
+// handleUpdateLoudnessSettings implements PUT /api/admin/library/loudness-settings.
+// A whole-row write: a body that leaves out the concurrency decodes it as zero,
+// which is refused rather than saved.
+func (h *handlers) handleUpdateLoudnessSettings(w http.ResponseWriter, r *http.Request) {
+	var req loudnessSettingsBody
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeErr(w, apierror.BadRequest("invalid_body", "malformed JSON"))
+		return
+	}
+	saved, err := h.loudnessSettings.Set(r.Context(), library.LoudnessSettings{
+		Enabled:             req.Enabled,
+		BackfillConcurrency: req.BackfillConcurrency,
+		LeveledCacheMB:      req.LeveledCacheMB,
+	})
+	if err != nil {
+		if errors.Is(err, library.ErrLoudnessSettingOutOfRange) {
+			writeErr(w, apierror.BadRequest("invalid_setting", err.Error()))
+			return
+		}
+		writeErrWithLog(w, h.logger, "admin loudness settings: update failed", apierror.Internal(err))
+		return
+	}
+	writeJSON(w, http.StatusOK, loudnessSettingsBodyOf(saved))
+}

internal/api/admin_network.go

@@ -23,10 +23,16 @@ type networkSettingsResp struct {
 	// arrived and count them rather than guess.
 	ForwardedChain string `json:"forwarded_chain"`
 	RemoteAddr     string `json:"remote_addr"`
+	// PublicURL is where users reach Minstrel; reset emails link to it and
+	// are not sent while it is empty.
+	PublicURL string `json:"public_url"`
 }
 
+// Both fields are optional so the proxy card and the public-address card can
+// each save their own value without overwriting the other's.
 type updateNetworkSettingsReq struct {
-	TrustedProxyHops int `json:"trusted_proxy_hops"`
+	TrustedProxyHops *int    `json:"trusted_proxy_hops"`
+	PublicURL        *string `json:"public_url"`
 }
 
 func (h *handlers) handleGetNetworkSettings(w http.ResponseWriter, r *http.Request) {
@@ -39,13 +45,37 @@ func (h *handlers) handleUpdateNetworkSettings(w http.ResponseWriter, r *http.Re
 		writeErr(w, apierror.BadRequest("invalid_body", "malformed JSON"))
 		return
 	}
-	if err := h.netSettings.SetHops(r.Context(), req.TrustedProxyHops); err != nil {
-		if errors.Is(err, netsettings.ErrHopsOutOfRange) {
-			writeErr(w, apierror.BadRequest("invalid_hops", err.Error()))
+	if req.TrustedProxyHops == nil && req.PublicURL == nil {
+		writeErr(w, apierror.BadRequest("invalid_body", "nothing to update"))
+		return
+	}
+	// Validate everything before writing anything, so a bad public URL can't
+	// leave the hops half-saved.
+	if req.TrustedProxyHops != nil && (*req.TrustedProxyHops < 0 || *req.TrustedProxyHops > netsettings.MaxTrustedProxyHops) {
+		writeErr(w, apierror.BadRequest("invalid_hops", netsettings.ErrHopsOutOfRange.Error()))
+		return
+	}
+	if req.PublicURL != nil {
+		if _, err := netsettings.NormalizePublicURL(*req.PublicURL); err != nil {
+			writeErr(w, apierror.BadRequest("invalid_public_url", err.Error()))
+			return
+		}
+	}
+	if req.TrustedProxyHops != nil {
+		if err := h.netSettings.SetHops(r.Context(), *req.TrustedProxyHops); err != nil {
+			if errors.Is(err, netsettings.ErrHopsOutOfRange) {
+				writeErr(w, apierror.BadRequest("invalid_hops", err.Error()))
+				return
+			}
+			writeErrWithLog(w, h.logger, "admin network: update failed", apierror.Internal(err))
+			return
+		}
+	}
+	if req.PublicURL != nil {
+		if err := h.netSettings.SetPublicURL(r.Context(), *req.PublicURL); err != nil {
+			writeErrWithLog(w, h.logger, "admin network: public URL update failed", apierror.Internal(err))
 			return
 		}
-		writeErrWithLog(w, h.logger, "admin network: update failed", apierror.Internal(err))
-		return
 	}
 	// Echo the payload recomputed under the NEW value, so the card can show
 	// immediately what the change did to this request's own address rather
@@ -61,5 +91,6 @@ func (h *handlers) networkSettingsPayload(r *http.Request) networkSettingsResp {
 		DetectedClientIP: auth.ClientIP(r, hops),
 		ForwardedChain:   r.Header.Get("X-Forwarded-For"),
 		RemoteAddr:       r.RemoteAddr,
+		PublicURL:        h.netSettings.PublicURL(),
 	}
 }

internal/api/admin_quarantine.go

@@ -133,6 +133,13 @@ func (h *handlers) handleDeleteQuarantineFile(w http.ResponseWriter, r *http.Req
 	}
 	action, err := h.lidarrQuarantine.DeleteFile(r.Context(), id, admin.ID)
 	if err != nil {
+		// Written in the enveloped shape, not writeAdminJSONErr's bare code: the
+		// message is the part that tells the operator which directory and uid.
+		if apiErr, ok := fileRemoveAPIError(err); ok {
+			logFileRemoveFailure(h.logger, apiErr, "track_id", uuidToString(id))
+			writeErr(w, apiErr)
+			return
+		}
 		switch {
 		case errors.Is(err, lidarrquarantine.ErrTrackNotFound):
 			writeAdminJSONErr(w, http.StatusNotFound, "track_not_found")

internal/api/admin_quarantine_test.go

@@ -69,7 +69,7 @@ func installQuarantineClientFn(t *testing.T, h *handlers) {
 		}
 		return lidarr.NewClient(c.BaseURL, c.APIKey)
 	}
-	h.lidarrQuarantine = lidarrquarantine.NewService(h.pool, cfg, clientFn)
+	h.lidarrQuarantine = lidarrquarantine.NewService(h.pool, cfg, clientFn, h.dataDir)
 }
 
 // flagDirect bypasses the HTTP handler to seed a quarantine row via the

internal/api/admin_tracks.go

@@ -23,15 +23,17 @@ type removeTrackResponse struct {
 
 // handleRemoveTrack implements DELETE /api/admin/tracks/{id}?unmonitor=true|false.
 //
-// Admin-only (gated by auth.RequireAdmin on the /admin route group). Always
-// deletes the file + DB row and runs the album/artist cascade tidy-up. When
+// Admin-only (gated by auth.RequireAdmin on the /admin route group). Deletes the
+// file, then the DB row, and runs the album/artist cascade tidy-up — and deletes
+// nothing at all when the file cannot be removed (#3918). When
 // unmonitor=true and the track has an mbid, also calls Lidarr.UnmonitorTrack
 // — failure there is non-fatal (the destructive part already completed) and
 // surfaces as `lidarr_unmonitor_failed: true` in the success envelope.
 //
 // Per spec §5, Lidarr-side errors during the unmonitor step do NOT map to
-// wire error codes; the only error codes this handler emits are not_found,
-// server_error, plus the auth codes the middleware emits upstream.
+// wire error codes. The codes this handler emits are not_found,
+// library_not_writable (409) and file_delete_failed when the file could not be
+// removed, server_error, plus the auth codes the middleware emits upstream.
 func (h *handlers) handleRemoveTrack(w http.ResponseWriter, r *http.Request) {
 	idStr := chi.URLParam(r, "id")
 	trackID, ok := parseUUID(idStr)
@@ -66,6 +68,11 @@ func (h *handlers) handleRemoveTrack(w http.ResponseWriter, r *http.Request) {
 			writeErr(w, &apierror.Error{Status: http.StatusNotFound, Code: "not_found", Message: "track not found"})
 			return
 		}
+		if apiErr, ok := fileRemoveAPIError(err); ok {
+			logFileRemoveFailure(h.logger, apiErr, "track_id", idStr)
+			writeErr(w, apiErr)
+			return
+		}
 		h.logger.Error("api: remove track failed", "err", err, "track_id", idStr)
 		writeErr(w, apierror.InternalMsg("remove failed", err))
 		return

internal/api/admin_users.go

@@ -169,7 +169,7 @@ func (h *handlers) handleAdminCreateUser(w http.ResponseWriter, r *http.Request)
 	user, err := q.CreateUserAdmin(r.Context(), dbq.CreateUserAdminParams{
 		Username:     req.Username,
 		PasswordHash: string(hash),
-		ApiToken:     apiToken,
+		ApiTokenHash: auth.HashAPIToken(apiToken),
 		IsAdmin:      req.IsAdmin,
 		DisplayName:  req.DisplayName,
 	})
@@ -285,6 +285,19 @@ func (h *handlers) handleAdminResetPassword(w http.ResponseWriter, r *http.Reque
 		return
 	}
 
+	// The target's existing sessions end with the old password. An admin
+	// resetting their own password keeps the session they're using, the
+	// same as a self-service change.
+	sessID, ownSession := auth.SessionIDFromContext(r.Context())
+	if targetID == caller.ID && ownSession {
+		_, err = q.DeleteOtherSessionsForUser(r.Context(), dbq.DeleteOtherSessionsForUserParams{UserID: targetID, ID: sessID})
+	} else {
+		_, err = q.DeleteSessionsForUser(r.Context(), targetID)
+	}
+	if err != nil {
+		h.logger.Error("admin reset password: revoke sessions failed", "err", err)
+	}
+
 	audit.WriteOrLog(r.Context(), h.pool, h.logger, caller.ID, targetID, audit.ActionPasswordResetAdmin, nil)
 
 	w.WriteHeader(http.StatusNoContent)

internal/api/api.go

@@ -7,6 +7,8 @@ package api
 import (
 	"log/slog"
 	"math/rand"
+	"path/filepath"
+	"time"
 
 	"github.com/go-chi/chi/v5"
 	"github.com/jackc/pgx/v5/pgxpool"
@@ -33,35 +35,54 @@ import (
 // Mount attaches /api/* handlers to r. Public endpoints (login) are outside
 // RequireUser; everything else is gated by the middleware. The events writer
 // is shared with the Subsonic mount so /rest/scrobble feeds the same store.
-func Mount(r chi.Router, pool *pgxpool.Pool, logger *slog.Logger, events *playevents.Writer, recCfg config.RecommendationConfig, recSettings *recsettings.Service, lidarrCfg *lidarrconfig.Service, lidarrReqs *lidarrrequests.Service, lidarrQuar *lidarrquarantine.Service, tracksSvc *tracks.Service, playlistsSvc *playlists.Service, coverEnricher *coverart.Enricher, coverSettings *coverart.SettingsService, tagSettings *tags.SettingsService, scanner *library.Scanner, scanCfg library.RunScanConfig, dataDir string, sender mailer.Sender, bus *eventbus.Bus, playlistScheduler *playlists.Scheduler, streamSecret []byte, netSettings *netsettings.Service, reacqSettings *reacquisition.SettingsService) {
+func Mount(r chi.Router, pool *pgxpool.Pool, logger *slog.Logger, events *playevents.Writer, recCfg config.RecommendationConfig, recSettings *recsettings.Service, lidarrCfg *lidarrconfig.Service, lidarrReqs *lidarrrequests.Service, lidarrQuar *lidarrquarantine.Service, tracksSvc *tracks.Service, playlistsSvc *playlists.Service, coverEnricher *coverart.Enricher, coverSettings *coverart.SettingsService, tagSettings *tags.SettingsService, scanner *library.Scanner, scanCfg library.RunScanConfig, dataDir string, sender mailer.Sender, bus *eventbus.Bus, playlistScheduler *playlists.Scheduler, streamSecret []byte, netSettings *netsettings.Service, reacqSettings *reacquisition.SettingsService, fpSettings *library.FingerprintSettingsService, loudSettings *library.LoudnessSettingsService, acoustIDLookup *library.AcoustIDLookupWorker) {
 	rng := rand.New(rand.NewSource(rand.Int63()))
+	setupToken, err := auth.NewSetupToken()
+	if err != nil {
+		// crypto/rand failing means the platform can't make secrets at all;
+		// sessions would be minted from the same source. Nothing to degrade to.
+		panic("api: mint setup token: " + err.Error())
+	}
+	logSetupTokenIfNeeded(pool, logger, setupToken)
 	h := &handlers{
 		pool: pool, logger: logger, events: events, recCfg: recCfg,
-		recSettings:       recSettings,
-		rng:               rng.Float64,
-		lidarrCfg:         lidarrCfg,
-		lidarrRequests:    lidarrReqs,
-		lidarrQuarantine:  lidarrQuar,
-		tracks:            tracksSvc,
-		playlists:         playlistsSvc,
-		coverart:          coverEnricher,
-		coverSettings:     coverSettings,
-		tagSettings:       tagSettings,
-		scanner:           scanner,
-		scanCfg:           scanCfg,
-		dataDir:           dataDir,
-		mailer:            sender,
-		eventbus:          bus,
-		playlistScheduler: playlistScheduler,
-		streamSecret:      streamSecret,
-		netSettings:       netSettings,
-		reacqSettings:     reacqSettings,
-		librarySize:       recommendation.NewLibrarySize(nil),
+		recSettings:         recSettings,
+		rng:                 rng.Float64,
+		lidarrCfg:           lidarrCfg,
+		lidarrRequests:      lidarrReqs,
+		lidarrQuarantine:    lidarrQuar,
+		tracks:              tracksSvc,
+		playlists:           playlistsSvc,
+		coverart:            coverEnricher,
+		coverSettings:       coverSettings,
+		tagSettings:         tagSettings,
+		scanner:             scanner,
+		scanCfg:             scanCfg,
+		dataDir:             dataDir,
+		mailer:              sender,
+		eventbus:            bus,
+		playlistScheduler:   playlistScheduler,
+		streamSecret:        streamSecret,
+		netSettings:         netSettings,
+		reacqSettings:       reacqSettings,
+		fingerprintSettings: fpSettings,
+		loudnessSettings:    loudSettings,
+		acoustIDLookup:      acoustIDLookup,
+		leveled:             newLeveledRenderer(dataDir, loudSettings, logger),
+		librarySize:         recommendation.NewLibrarySize(nil),
+		loginGuard:          auth.NewLoginGuard(),
+		setupToken:          setupToken,
+		requireSetupToken:   true,
+		registerLimit:       auth.NewAttemptLimiter(registerPerAddressMax, time.Hour),
+		forgotAddressLimit:  auth.NewAttemptLimiter(forgotPerAddressMax, time.Hour),
+		forgotEmailLimit:    auth.NewAttemptLimiter(forgotPerEmailMax, time.Hour),
+		resetLimit:          auth.NewAttemptLimiter(resetFailuresPerAddressMax, 15*time.Minute),
 	}
 
 	r.Route("/api", func(api chi.Router) {
 		api.Post("/auth/login", h.handleLogin)
 		api.Post("/auth/register", h.handleRegister)
+		api.Get("/auth/setup-status", h.handleSetupStatus)
 		api.Post("/auth/forgot-password", h.handleForgotPassword)
 		api.Post("/auth/reset-password", h.handleResetPassword)
 
@@ -78,6 +99,9 @@ func Mount(r chi.Router, pool *pgxpool.Pool, logger *slog.Logger, events *playev
 		// audio format from the path. The {ext} param is consumed by chi
 		// and ignored by the handler (which keys off {id}). See task #610.
 		api.With(auth.OptionalUser(pool, logger)).Get("/tracks/{id}/stream.{ext}", h.handleGetStream)
+		// The leveled stream for Sonos/UPnP (M464 #5001): session or a
+		// leveled token, like the plain stream.
+		api.With(auth.OptionalUser(pool, logger)).Get("/tracks/{id}/leveled.flac", h.handleGetLeveledStream)
 
 		api.Group(func(authed chi.Router) {
 			authed.Use(auth.RequireUser(pool, netSettings.Hops))
@@ -91,8 +115,12 @@ func Mount(r chi.Router, pool *pgxpool.Pool, logger *slog.Logger, events *playev
 			authed.Put("/me/password", h.handleChangePassword)
 			authed.Put("/me/profile", h.handleUpdateMyProfile)
 			authed.Put("/me/timezone", h.handlePutTimezone)
-			authed.Get("/me/api-token", h.handleGetMyAPIToken)
+			authed.Get("/me/normalization", h.handleGetMyNormalization)
+			authed.Put("/me/normalization", h.handlePutMyNormalization)
 			authed.Post("/me/api-token", h.handleRegenerateMyAPIToken)
+			authed.Get("/me/subsonic-password", h.handleGetMySubsonicPassword)
+			authed.Post("/me/subsonic-password", h.handleGenerateMySubsonicPassword)
+			authed.Delete("/me/subsonic-password", h.handleClearMySubsonicPassword)
 			authed.Get("/me/sessions", h.handleListMySessions)
 			authed.Delete("/me/sessions/{id}", h.handleRevokeMySession)
 			authed.Post("/me/sessions/logout-others", h.handleRevokeMyOtherSessions)
@@ -112,6 +140,9 @@ func Mount(r chi.Router, pool *pgxpool.Pool, logger *slog.Logger, events *playev
 			authed.Get("/library/genres", h.handleListGenres)
 			authed.Get("/library/years", h.handleListAlbumYears)
 			authed.Get("/library/sync", h.handleLibrarySync)
+			// Before /tracks/{id} for readability; chi prefers the static
+			// segment either way.
+			authed.Get("/tracks/replay-gain", h.handleGetReplayGain)
 			authed.Get("/tracks/{id}", h.handleGetTrack)
 			// /tracks/{id}/stream is mounted above with OptionalUser so
 			// it can accept either a session or a signed token.
@@ -215,6 +246,23 @@ func Mount(r chi.Router, pool *pgxpool.Pool, logger *slog.Logger, events *playev
 				admin.Get("/library/missing", h.handleListMissingTracks)
 
 				admin.Get("/library/coverage", h.handleGetLibraryCoverage)
+				admin.Get("/library/fingerprints", h.handleGetFingerprintCoverage)
+				admin.Get("/library/fingerprint-settings", h.handleGetFingerprintSettings)
+				admin.Put("/library/fingerprint-settings", h.handleUpdateFingerprintSettings)
+				admin.Get("/library/loudness", h.handleGetLoudnessCoverage)
+				admin.Get("/library/loudness-settings", h.handleGetLoudnessSettings)
+				admin.Put("/library/loudness-settings", h.handleUpdateLoudnessSettings)
+				admin.Get("/library/acoustid", h.handleGetAcoustID)
+				admin.Put("/library/acoustid-settings", h.handleUpdateAcoustIDSettings)
+				admin.Post("/library/acoustid/run", h.handleRunAcoustIDLookup)
+				admin.Get("/library/acoustid/unsettled", h.handleListUnsettledAcoustID)
+				// Duplicates report (#3912): proposals from the duplicate sweep, a
+				// trigger to sweep now, dismissal, and the merge (#3911), which deletes
+				// the removed copies' files after moving their history onto the kept one.
+				admin.Get("/library/duplicates", h.handleListDuplicates)
+				admin.Post("/library/duplicates/sweep", h.handleRunDuplicateSweep)
+				admin.Post("/library/duplicates/{id}/dismiss", h.handleDismissDuplicateGroup)
+				admin.Post("/library/duplicates/{id}/merge", h.handleMergeDuplicateGroup)
 
 				admin.Get("/invites", h.handleListInvites)
 				admin.Post("/invites", h.handleCreateInvite)
@@ -298,6 +346,34 @@ type handlers struct {
 	// missing files (milestone #290) — grace window, backoff, attempt caps.
 	// Cached in the service, so the admin card reads it without a query.
 	reacqSettings *reacquisition.SettingsService
+	// fingerprintSettings is the fingerprinting policy (M400 #3913), the same
+	// instance the scanner and the fingerprint workers read, so a save from the
+	// admin card reaches them without a restart. Nil serves the defaults.
+	fingerprintSettings *library.FingerprintSettingsService
+	// loudnessSettings is the loudness analysis policy (M464 #4995), the same
+	// instance the loudness backfill reads. Nil serves the defaults.
+	loudnessSettings *library.LoudnessSettingsService
+	// acoustIDLookup is the AcoustID lookup worker (M401): its settings, its
+	// status and "look up now". Nil serves the defaults (off).
+	acoustIDLookup *library.AcoustIDLookupWorker
+	// leveled renders the leveled streams handed to Sonos/UPnP speakers
+	// (M464 #5001). Nil when its cache directory cannot be made: a level
+	// request then gets the plain stream.
+	leveled *library.LeveledRenderer
+	// setupToken must accompany the first registration while no users exist
+	// (see auth.SetupToken). requireSetupToken is set by Mount, the only
+	// production constructor; tests that build handlers directly leave it
+	// off unless they are testing it.
+	setupToken        *auth.SetupToken
+	requireSetupToken bool
+	// loginGuard throttles failed logins per account and per address, and
+	// the limiters below cap the other unauthenticated auth routes. All are
+	// nil-safe, so tests that build handlers directly run unthrottled.
+	loginGuard         *auth.LoginGuard
+	registerLimit      *auth.AttemptLimiter
+	forgotAddressLimit *auth.AttemptLimiter
+	forgotEmailLimit   *auth.AttemptLimiter
+	resetLimit         *auth.AttemptLimiter
 	// netSettings caches the trusted reverse-proxy depth read by the auth
 	// middleware on every request and edited from the admin network card.
 	netSettings *netsettings.Service
@@ -311,3 +387,14 @@ type handlers struct {
 	// anything a client mints), which is the desired slice-1 default.
 	streamSecret []byte
 }
+
+// newLeveledRenderer makes the leveled-stream renderer, caching under the
+// data directory. A failure is logged and leaves leveling off for speakers.
+func newLeveledRenderer(dataDir string, settings *library.LoudnessSettingsService, logger *slog.Logger) *library.LeveledRenderer {
+	r, err := library.NewLeveledRenderer(filepath.Join(dataDir, "leveled-cache"), settings, logger)
+	if err != nil {
+		logger.Error("api: leveled streams unavailable", "err", err)
+		return nil
+	}
+	return r
+}

internal/api/auth.go

@@ -19,6 +19,20 @@ import (
 // so an abandoned laptop doesn't stay logged in forever.
 const sessionCookieMaxAge = 30 * 24 * time.Hour
 
+// Limits on the unauthenticated auth routes other than login (which uses
+// auth.LoginGuard). Per address, per window as wired in Mount.
+const (
+	// registerPerAddressMax: 10 registrations an hour. Every attempt counts,
+	// typos included, which is still far above a household's need.
+	registerPerAddressMax = 10
+	// forgotPerAddressMax / forgotPerEmailMax: reset emails an hour. The
+	// per-email cap is what keeps one inbox from being mailbombed.
+	forgotPerAddressMax = 5
+	forgotPerEmailMax   = 3
+	// resetFailuresPerAddressMax: wrong or expired reset tokens per 15 min.
+	resetFailuresPerAddressMax = 20
+)
+
 func (h *handlers) handleLogout(w http.ResponseWriter, r *http.Request) {
 	// The session token can be on the cookie OR bearer header — RequireUser
 	// accepted either. Re-resolve it here so we can delete the row.
@@ -70,10 +84,22 @@ func (h *handlers) handleLogin(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// Checked before any lookup or bcrypt, so a throttled guess costs the
+	// server nothing and learns nothing.
+	addr := auth.ClientIP(r, h.netSettings.Hops())
+	if blocked, wait := h.loginGuard.Blocked(req.Username, addr); blocked {
+		writeRateLimited(w, wait)
+		return
+	}
+
 	q := dbq.New(h.pool)
 	user, err := q.GetUserByUsername(r.Context(), req.Username)
 	if err != nil {
 		if errors.Is(err, pgx.ErrNoRows) {
+			// Same bcrypt time as a wrong password, so timing doesn't say
+			// which usernames exist.
+			auth.DummyVerify(req.Password)
+			h.loginGuard.Fail(req.Username, addr)
 			writeErr(w, apierror.Unauthorized("invalid_credentials", "invalid username or password"))
 			return
 		}
@@ -82,9 +108,11 @@ func (h *handlers) handleLogin(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	if !auth.VerifyPassword(user.PasswordHash, req.Password) {
+		h.loginGuard.Fail(req.Username, addr)
 		writeErr(w, apierror.Unauthorized("invalid_credentials", "invalid username or password"))
 		return
 	}
+	h.loginGuard.Succeed(req.Username)
 
 	token, err := auth.MintSessionToken()
 	if err != nil {
@@ -100,7 +128,7 @@ func (h *handlers) handleLogin(w http.ResponseWriter, r *http.Request) {
 		// the active-sessions surface: a session that was born somewhere the
 		// user recognises but is being used from somewhere they don't is the
 		// case this whole surface exists to surface.
-		Ip: auth.ClientIP(r, h.netSettings.Hops()),
+		Ip: addr,
 	}); err != nil {
 		h.logger.Error("api: insert session failed", "err", err)
 		writeErr(w, apierror.InternalMsg("insert failed", err))
@@ -112,7 +140,7 @@ func (h *handlers) handleLogin(w http.ResponseWriter, r *http.Request) {
 		Value:    token,
 		Path:     "/",
 		HttpOnly: true,
-		Secure:   r.TLS != nil, // dev over http stays functional; prod over https gets Secure
+		Secure:   auth.IsHTTPS(r, h.netSettings.Hops()), // plain HTTP and LAN stay functional (rule 94)
 		SameSite: http.SameSiteStrictMode,
 		MaxAge:   int(sessionCookieMaxAge.Seconds()),
 	})

internal/api/auth_forgot.go

@@ -14,6 +14,7 @@ import (
 	"github.com/jackc/pgx/v5/pgtype"
 
 	"git.fabledsword.com/bvandeusen/minstrel/internal/audit"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/auth"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/mailer"
 )
@@ -47,6 +48,19 @@ func (h *handlers) handleForgotPassword(w http.ResponseWriter, r *http.Request)
 	}
 	email := strings.ToLower(strings.TrimSpace(req.Email))
 
+	// Throttled per address (a spray) and per email (a mailbomb of one
+	// inbox). Applied whether or not the email matches, so a 429 says
+	// nothing about which addresses are registered.
+	addr := auth.ClientIP(r, h.netSettings.Hops())
+	blockedAddr, waitAddr := h.forgotAddressLimit.Blocked(addr)
+	blockedEmail, waitEmail := h.forgotEmailLimit.Blocked(email)
+	if blockedAddr || blockedEmail {
+		writeRateLimited(w, max(waitAddr, waitEmail))
+		return
+	}
+	h.forgotAddressLimit.Record(addr)
+	h.forgotEmailLimit.Record(email)
+
 	q := dbq.New(h.pool)
 	var matched bool
 	var auditTarget pgtype.UUID
@@ -55,7 +69,7 @@ func (h *handlers) handleForgotPassword(w http.ResponseWriter, r *http.Request)
 		if err == nil && user.Email != nil && *user.Email != "" {
 			matched = true
 			auditTarget = user.ID
-			if sendErr := h.sendResetEmail(r.Context(), r, user); sendErr != nil {
+			if sendErr := h.sendResetEmail(r.Context(), user); sendErr != nil {
 				h.logger.Warn("forgot-password: send failed",
 					"email", email, "err", sendErr)
 				// fall through; response is still 200
@@ -75,7 +89,7 @@ func (h *handlers) handleForgotPassword(w http.ResponseWriter, r *http.Request)
 // sendResetEmail generates a token, persists it, renders + sends the
 // email. Returns the underlying error (caller logs it but doesn't
 // surface to the HTTP response).
-func (h *handlers) sendResetEmail(ctx context.Context, r *http.Request, user dbq.User) error {
+func (h *handlers) sendResetEmail(ctx context.Context, user dbq.User) error {
 	if h.mailer == nil {
 		return errors.New("forgot-password: no mailer configured")
 	}
@@ -95,7 +109,10 @@ func (h *handlers) sendResetEmail(ctx context.Context, r *http.Request, user dbq
 		return err
 	}
 
-	resetURL := buildResetURL(r, token)
+	resetURL, err := buildResetURL(h.netSettings.PublicURL(), token)
+	if err != nil {
+		return err
+	}
 	textBody, htmlBody, err := mailer.RenderResetEmail(mailer.ResetEmailVars{
 		Username:    user.Username,
 		ResetURL:    resetURL,
@@ -113,14 +130,18 @@ func (h *handlers) sendResetEmail(ctx context.Context, r *http.Request, user dbq
 	return h.mailer.Send(ctx, *user.Email, mailer.ResetEmailSubject, textBody, htmlBody)
 }
 
-func buildResetURL(r *http.Request, token string) string {
-	scheme := "http"
-	if r.TLS != nil {
-		scheme = "https"
+// errNoPublicURL stops a reset email from going out before the operator has
+// said where Minstrel lives. It surfaces in the log, not the response, which
+// stays the same opaque 200 either way.
+var errNoPublicURL = errors.New("forgot-password: no public URL set (Admin → Integrations → Public address); reset email not sent")
+
+// buildResetURL builds the emailed link from the operator-set public URL.
+// It deliberately ignores the request: the Host header is whatever the
+// requester sent, and building from it let a forged Host plant a real reset
+// token on a link to someone else's server.
+func buildResetURL(publicURL, token string) (string, error) {
+	if publicURL == "" {
+		return "", errNoPublicURL
 	}
-	host := r.Host
-	if host == "" {
-		host = "localhost"
-	}
-	return scheme + "://" + host + "/reset-password/" + token
+	return publicURL + "/reset-password/" + token, nil
 }

internal/api/auth_forgot_test.go

@@ -7,11 +7,59 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"os"
+	"strings"
 	"testing"
 
+	"github.com/jackc/pgx/v5/pgxpool"
+
 	"git.fabledsword.com/bvandeusen/minstrel/internal/mailer"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/netsettings"
 )
 
+// withPublicURL gives h a network-settings service holding url, restoring an
+// empty value afterwards so other tests see the default.
+func withPublicURL(t *testing.T, h *handlers, pool *pgxpool.Pool, url string) {
+	t.Helper()
+	ns, err := netsettings.New(context.Background(), pool, nil)
+	if err != nil {
+		t.Fatalf("netsettings: %v", err)
+	}
+	if err := ns.SetPublicURL(context.Background(), url); err != nil {
+		t.Fatalf("set public url: %v", err)
+	}
+	t.Cleanup(func() { _ = ns.SetPublicURL(context.Background(), "") })
+	h.netSettings = ns
+}
+
+// With no public URL set, a reset email is not sent at all, and the response
+// is still the same opaque 200.
+func TestForgotPassword_NoPublicURL_SendsNothing(t *testing.T) {
+	if os.Getenv("MINSTREL_TEST_DATABASE_URL") == "" {
+		t.Skip("MINSTREL_TEST_DATABASE_URL not set")
+	}
+	h, pool := testHandlers(t)
+	fake := &mailer.FakeSender{}
+	h.mailer = fake
+	withPublicURL(t, h, pool, "")
+
+	user := seedUser(t, pool, "nourl", "pw", false)
+	if _, err := pool.Exec(context.Background(),
+		"UPDATE users SET email = 'nourl@example.com' WHERE id = $1", user.ID); err != nil {
+		t.Fatalf("seed email: %v", err)
+	}
+	req := httptest.NewRequest(http.MethodPost, "/api/auth/forgot-password",
+		bytes.NewReader([]byte(`{"email":"nourl@example.com"}`)))
+	rec := httptest.NewRecorder()
+	h.handleForgotPassword(rec, req)
+
+	if rec.Code != http.StatusOK {
+		t.Errorf("status = %d, want 200", rec.Code)
+	}
+	if len(fake.Sent) != 0 {
+		t.Errorf("sent %d emails with no public URL set, want 0", len(fake.Sent))
+	}
+}
+
 func TestForgotPassword_KnownEmail_SendsMail(t *testing.T) {
 	if os.Getenv("MINSTREL_TEST_DATABASE_URL") == "" {
 		t.Skip("MINSTREL_TEST_DATABASE_URL not set")
@@ -19,6 +67,7 @@ func TestForgotPassword_KnownEmail_SendsMail(t *testing.T) {
 	h, pool := testHandlers(t)
 	fake := &mailer.FakeSender{}
 	h.mailer = fake
+	withPublicURL(t, h, pool, "https://music.example.com")
 
 	user := seedUser(t, pool, "forgotuser", "pw", false)
 	if _, err := pool.Exec(context.Background(),
@@ -29,7 +78,8 @@ func TestForgotPassword_KnownEmail_SendsMail(t *testing.T) {
 	body := `{"email":"forgot@example.com"}`
 	req := httptest.NewRequest(http.MethodPost, "/api/auth/forgot-password",
 		bytes.NewReader([]byte(body)))
-	req.Host = "minstrel.example.com"
+	// A forged Host must not reach the link: it comes from the public URL.
+	req.Host = "attacker.example.net"
 	rec := httptest.NewRecorder()
 	h.handleForgotPassword(rec, req)
 
@@ -43,6 +93,12 @@ func TestForgotPassword_KnownEmail_SendsMail(t *testing.T) {
 	if got.To != "forgot@example.com" {
 		t.Errorf("To = %q, want forgot@example.com", got.To)
 	}
+	if !strings.Contains(got.TextBody, "https://music.example.com/reset-password/") {
+		t.Errorf("reset link not built from the public URL:\n%s", got.TextBody)
+	}
+	if strings.Contains(got.TextBody+got.HTMLBody, "attacker.example.net") {
+		t.Error("the request's Host header reached the emailed link")
+	}
 	// Token row was inserted.
 	var tokenCount int
 	if err := pool.QueryRow(context.Background(),

internal/api/auth_register.go

@@ -1,8 +1,10 @@
 package api
 
 import (
+	"context"
 	"encoding/json"
 	"errors"
+	"log/slog"
 	"net/http"
 	"regexp"
 	"time"
@@ -10,6 +12,7 @@ import (
 	"github.com/jackc/pgerrcode"
 	"github.com/jackc/pgx/v5"
 	"github.com/jackc/pgx/v5/pgconn"
+	"github.com/jackc/pgx/v5/pgxpool"
 	"golang.org/x/crypto/bcrypt"
 
 	"git.fabledsword.com/bvandeusen/minstrel/internal/apierror"
@@ -26,9 +29,12 @@ var usernameRe = regexp.MustCompile(`^[a-zA-Z0-9_-]{3,32}$`)
 const minPasswordLength = 8
 
 type registerReq struct {
-	Username    string  `json:"username"`
-	Password    string  `json:"password"`
-	InviteToken string  `json:"invite_token"`
+	Username    string `json:"username"`
+	Password    string `json:"password"`
+	InviteToken string `json:"invite_token"`
+	// SetupToken is required only for the very first account; see
+	// auth.SetupToken.
+	SetupToken  string  `json:"setup_token"`
 	DisplayName *string `json:"display_name"`
 }
 
@@ -55,6 +61,15 @@ type registerReq struct {
 //   - 409 username_taken (PG unique violation on users.username)
 //   - 500 server_error otherwise
 func (h *handlers) handleRegister(w http.ResponseWriter, r *http.Request) {
+	// Every attempt counts, not only failures: a successful registration is
+	// the thing being sprayed when the mode is open.
+	addr := auth.ClientIP(r, h.netSettings.Hops())
+	if blocked, wait := h.registerLimit.Blocked(addr); blocked {
+		writeRateLimited(w, wait)
+		return
+	}
+	h.registerLimit.Record(addr)
+
 	var req registerReq
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
 		writeErr(w, apierror.BadRequest("invalid_body", "invalid JSON body"))
@@ -79,6 +94,19 @@ func (h *handlers) handleRegister(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// The first account becomes admin, so it must prove it can read the
+	// server log. Checked before the invite logic, which the empty-users
+	// state skips.
+	if userCount == 0 && h.requireSetupToken && !h.setupToken.Matches(req.SetupToken) {
+		// Repeat the token in the log at the moment someone needs it: the
+		// boot line may have scrolled away, or users may have been deleted
+		// since boot.
+		h.logger.Warn("register: first-admin registration needs the setup token",
+			"setup_token", h.setupToken.Value())
+		writeErr(w, apierror.Forbidden("setup_token_invalid", "the setup token from the server log is required to create the first account"))
+		return
+	}
+
 	// Validate invite (skipped on empty-users state; skipped in 'open' mode).
 	usedInviteToken := ""
 	if userCount > 0 {
@@ -133,7 +161,7 @@ func (h *handlers) handleRegister(w http.ResponseWriter, r *http.Request) {
 	user, err := q.CreateUserFirstAdminRace(r.Context(), dbq.CreateUserFirstAdminRaceParams{
 		Username:     req.Username,
 		PasswordHash: string(hash),
-		ApiToken:     apiToken,
+		ApiTokenHash: auth.HashAPIToken(apiToken),
 		DisplayName:  req.DisplayName,
 	})
 	if err != nil {
@@ -175,7 +203,7 @@ func (h *handlers) handleRegister(w http.ResponseWriter, r *http.Request) {
 		UserID:    user.ID,
 		TokenHash: auth.HashSessionToken(sessionToken),
 		UserAgent: r.UserAgent(),
-		Ip:        auth.ClientIP(r, h.netSettings.Hops()),
+		Ip:        addr,
 	}); err != nil {
 		h.logger.Error("register: insert session failed", "err", err)
 		writeErr(w, apierror.Internal(err))
@@ -186,7 +214,7 @@ func (h *handlers) handleRegister(w http.ResponseWriter, r *http.Request) {
 		Value:    sessionToken,
 		Path:     "/",
 		HttpOnly: true,
-		Secure:   r.TLS != nil,
+		Secure:   auth.IsHTTPS(r, h.netSettings.Hops()), // plain HTTP and LAN stay functional (rule 94)
 		SameSite: http.SameSiteStrictMode,
 		MaxAge:   int(sessionCookieMaxAge.Seconds()),
 	})
@@ -223,3 +251,31 @@ func (h *handlers) handleRegister(w http.ResponseWriter, r *http.Request) {
 		},
 	})
 }
+
+// handleSetupStatus implements GET /api/auth/setup-status. It tells the
+// register screen whether to ask for the setup token, i.e. whether no
+// account exists yet. Public, since it is needed before anyone can sign in;
+// "this server has no users" is not worth hiding from someone who could
+// simply try to register.
+func (h *handlers) handleSetupStatus(w http.ResponseWriter, r *http.Request) {
+	n, err := dbq.New(h.pool).CountUsers(r.Context())
+	if err != nil {
+		writeErrWithLog(w, h.logger, "setup status: count users failed", apierror.Internal(err))
+		return
+	}
+	writeJSON(w, http.StatusOK, map[string]bool{"setup_required": n == 0})
+}
+
+// logSetupTokenIfNeeded writes the setup token to the log at boot when the
+// instance has no accounts yet, with the instruction for using it.
+func logSetupTokenIfNeeded(pool *pgxpool.Pool, logger *slog.Logger, token *auth.SetupToken) {
+	if pool == nil || logger == nil {
+		return
+	}
+	n, err := dbq.New(pool).CountUsers(context.Background())
+	if err != nil || n > 0 {
+		return
+	}
+	logger.Warn("no accounts yet: open the web app, choose Create account, and enter this setup token to become the admin",
+		"setup_token", token.Value())
+}

internal/api/auth_register_test.go

@@ -273,3 +273,75 @@ func TestRegister_FirstAdminRace(t *testing.T) {
 	// not "exactly one" (which would require serializable isolation).
 	t.Logf("admin count after race = %d (>=1 is the invariant)", adminCount)
 }
+
+// With the gate on (as Mount sets it), the first account needs the setup
+// token from the log; a missing or wrong one is refused and creates nothing.
+func TestRegister_FirstUserNeedsSetupToken(t *testing.T) {
+	if os.Getenv("MINSTREL_TEST_DATABASE_URL") == "" {
+		t.Skip("MINSTREL_TEST_DATABASE_URL not set")
+	}
+	h, _ := testHandlers(t)
+	resetUsers(t, h)
+	token, err := auth.NewSetupToken()
+	if err != nil {
+		t.Fatalf("mint: %v", err)
+	}
+	h.setupToken = token
+	h.requireSetupToken = true
+
+	register := func(body string) int {
+		req := httptest.NewRequest(http.MethodPost, "/api/auth/register", bytes.NewReader([]byte(body)))
+		rec := httptest.NewRecorder()
+		h.handleRegister(rec, req)
+		return rec.Code
+	}
+
+	if code := register(`{"username":"squatter","password":"abcd1234"}`); code != http.StatusForbidden {
+		t.Errorf("no token: status = %d, want 403", code)
+	}
+	if code := register(`{"username":"squatter","password":"abcd1234","setup_token":"wrong"}`); code != http.StatusForbidden {
+		t.Errorf("wrong token: status = %d, want 403", code)
+	}
+	var n int
+	if err := h.pool.QueryRow(context.Background(), `SELECT count(*) FROM users`).Scan(&n); err != nil {
+		t.Fatalf("count: %v", err)
+	}
+	if n != 0 {
+		t.Fatalf("a refused registration created %d account(s)", n)
+	}
+
+	if code := register(`{"username":"operator","password":"abcd1234","setup_token":"` + token.Value() + `"}`); code != http.StatusOK {
+		t.Fatalf("right token: status = %d, want 200", code)
+	}
+
+	// Once an account exists the token plays no part: the second user is
+	// governed by registration mode, not the setup token.
+	if _, err := h.pool.Exec(context.Background(),
+		`UPDATE registration_settings SET mode = 'open' WHERE id = true`); err != nil {
+		t.Fatalf("open mode: %v", err)
+	}
+	t.Cleanup(func() {
+		_, _ = h.pool.Exec(context.Background(),
+			`UPDATE registration_settings SET mode = 'invite_only' WHERE id = true`)
+	})
+	if code := register(`{"username":"second","password":"abcd1234"}`); code != http.StatusOK {
+		t.Errorf("second user without token: status = %d, want 200", code)
+	}
+}
+
+func TestSetupToken_MatchesOnlyItself(t *testing.T) {
+	tok, err := auth.NewSetupToken()
+	if err != nil {
+		t.Fatalf("mint: %v", err)
+	}
+	if !tok.Matches(tok.Value()) {
+		t.Error("token does not match itself")
+	}
+	if tok.Matches("") || tok.Matches(tok.Value()+"x") {
+		t.Error("token matched something else")
+	}
+	var none *auth.SetupToken
+	if none.Matches("") || none.Matches("anything") {
+		t.Error("a nil token must fail closed")
+	}
+}

internal/api/auth_reset.go

@@ -10,6 +10,7 @@ import (
 
 	"git.fabledsword.com/bvandeusen/minstrel/internal/apierror"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/audit"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/auth"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
 )
 
@@ -42,6 +43,15 @@ func (h *handlers) handleResetPassword(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// Tokens carry 256 bits, so guessing one is hopeless; the limit is on
+	// failed tries per address so that nobody gets to find that out at our
+	// expense.
+	addr := auth.ClientIP(r, h.netSettings.Hops())
+	if blocked, wait := h.resetLimit.Blocked(addr); blocked {
+		writeRateLimited(w, wait)
+		return
+	}
+
 	q := dbq.New(h.pool)
 
 	// Look up the reset record so we know which user to update before
@@ -50,6 +60,7 @@ func (h *handlers) handleResetPassword(w http.ResponseWriter, r *http.Request) {
 	reset, err := q.GetPasswordReset(r.Context(), req.Token)
 	if err != nil {
 		if errors.Is(err, pgx.ErrNoRows) {
+			h.resetLimit.Record(addr)
 			writeErr(w, apierror.BadRequest("invalid_token", ""))
 			return
 		}
@@ -69,6 +80,7 @@ func (h *handlers) handleResetPassword(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	if rows == 0 {
+		h.resetLimit.Record(addr)
 		writeErr(w, apierror.BadRequest("invalid_token", ""))
 		return
 	}
@@ -92,6 +104,13 @@ func (h *handlers) handleResetPassword(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// End every session the account has. Whoever needed a reset isn't signed
+	// in anywhere they rely on, and whoever may have learned the old password
+	// must not stay signed in on it.
+	if _, err := q.DeleteSessionsForUser(r.Context(), reset.UserID); err != nil {
+		h.logger.Error("reset password: revoke sessions failed", "err", err)
+	}
+
 	audit.WriteOrLog(r.Context(), h.pool, h.logger, reset.UserID, reset.UserID, audit.ActionPasswordResetByEmail, nil)
 
 	w.WriteHeader(http.StatusNoContent)

internal/api/auth_test.go

@@ -65,7 +65,7 @@ func testHandlers(t *testing.T) (*handlers, *pgxpool.Pool) {
 	}
 	lidarrCfg := lidarrconfig.New(pool)
 	lidarrReqs := lidarrrequests.NewService(pool, lidarrCfg, nil, nil)
-	lidarrQuar := lidarrquarantine.NewService(pool, lidarrCfg, nil)
+	lidarrQuar := lidarrquarantine.NewService(pool, lidarrCfg, nil, "")
 	// tracks.Service has no Lidarr unmonitorer in tests by default; the
 	// admin-tracks tests below override h.tracks via installTracksLidarrStub
 	// when they need a stubbed Lidarr.
@@ -91,7 +91,7 @@ func seedUser(t *testing.T, pool *pgxpool.Pool, username, password string, isAdm
 	u, err := dbq.New(pool).CreateUser(context.Background(), dbq.CreateUserParams{
 		Username:     prefixed,
 		PasswordHash: string(hash),
-		ApiToken:     "test-api-token-" + prefixed,
+		ApiTokenHash: "test-api-token-" + prefixed,
 		IsAdmin:      isAdmin,
 	})
 	if err != nil {
@@ -179,6 +179,36 @@ func TestHandleLogin_UnknownUserReturns401(t *testing.T) {
 	}
 }
 
+// A guesser who reaches the account limit is refused with 429 before any
+// password check, so even the right password is turned away until the window
+// passes, and the response says when to come back.
+func TestHandleLogin_ThrottledAfterRepeatedFailures(t *testing.T) {
+	h, pool := testHandlers(t)
+	h.loginGuard = auth.NewLoginGuard()
+	seedUser(t, pool, "alice", "hunter2", false)
+
+	login := func(password string) *httptest.ResponseRecorder {
+		body := strings.NewReader(`{"username":"test-alice","password":"` + password + `"}`)
+		req := httptest.NewRequest(http.MethodPost, "/api/auth/login", body)
+		req.Header.Set("Content-Type", "application/json")
+		w := httptest.NewRecorder()
+		h.handleLogin(w, req)
+		return w
+	}
+	for i := 0; i < 10; i++ {
+		if w := login("wrong"); w.Code != http.StatusUnauthorized {
+			t.Fatalf("attempt %d: status = %d, want 401", i+1, w.Code)
+		}
+	}
+	w := login("hunter2")
+	if w.Code != http.StatusTooManyRequests {
+		t.Fatalf("status = %d, want 429 once the account limit is reached", w.Code)
+	}
+	if w.Header().Get("Retry-After") == "" {
+		t.Error("429 without Retry-After")
+	}
+}
+
 func TestHandleLogin_MalformedBodyReturns400(t *testing.T) {
 	h, _ := testHandlers(t)
 	req := httptest.NewRequest(http.MethodPost, "/api/auth/login",

internal/api/cast_token.go

@@ -8,6 +8,7 @@ import (
 
 	"git.fabledsword.com/bvandeusen/minstrel/internal/apierror"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/library"
 )
 
 const (
@@ -19,6 +20,17 @@ const (
 type castTokenRequest struct {
 	TrackID    string `json:"trackId"`
 	ExpSeconds int    `json:"expSeconds,omitempty"`
+	// Level asks for the leveled stream (M464 #5001): the track rendered at
+	// the user's loudness gain. AsAlbum says the track is playing as part of
+	// its album in order, which picks album gain in auto mode; only the
+	// client holding the queue knows it.
+	Level   bool `json:"level,omitempty"`
+	AsAlbum bool `json:"asAlbum,omitempty"`
+	// Prerender says the speaker will fetch this track soon: the current
+	// track at a queue load, or the next one as it starts. Only those are
+	// rendered ahead; a queue load mints every track and renders none of
+	// the rest until the speaker asks.
+	Prerender bool `json:"prerender,omitempty"`
 }
 
 type castTokenResponse struct {
@@ -31,6 +43,10 @@ type castTokenResponse struct {
 	// `<res protocolInfo>` and `<dc:title>` without a follow-up round trip.
 	MIME  string `json:"mime"`
 	Title string `json:"title"`
+	// Leveled is true when URL is the leveled stream. A level request still
+	// gets the plain stream when there is nothing to change: leveling off,
+	// the track not yet measured, or a gain of 0.
+	Leveled bool `json:"leveled"`
 }
 
 // mimeForFormat returns the audio MIME type for a cast (Sonos/UPnP) URL.
@@ -89,7 +105,8 @@ func extForFormat(format string) string {
 // Part of the output-picker UPnP slice. See
 // docs/superpowers/specs/2026-06-03-android-output-picker-upnp-design.md.
 func (h *handlers) handleCastStreamToken(w http.ResponseWriter, r *http.Request) {
-	if _, ok := requireUser(w, r); !ok {
+	user, ok := requireUser(w, r)
+	if !ok {
 		return
 	}
 	var req castTokenRequest
@@ -112,6 +129,27 @@ func (h *handlers) handleCastStreamToken(w http.ResponseWriter, r *http.Request)
 	expSec := clampExpSeconds(req.ExpSeconds)
 	exp := time.Now().Add(time.Duration(expSec) * time.Second).Unix()
 	token := SignStreamToken(h.streamSecret, req.TrackID, exp)
+	path := streamURLWithExt(trackUUID, extForFormat(track.FileFormat)) +
+		"?token=" + token + "&exp=" + strconv.FormatInt(exp, 10)
+	mime := mimeForFormat(track.FileFormat)
+	leveled := false
+	if req.Level && h.leveled != nil {
+		g, err := h.leveledGainFor(r.Context(), user.ID, trackUUID, req.AsAlbum)
+		if err != nil {
+			// The plain stream still plays; only the leveling is lost.
+			h.logger.Warn("cast token: leveled gain lookup failed", "track", req.TrackID, "err", err)
+		} else if !g.Unity() {
+			token = SignLeveledStreamToken(h.streamSecret, req.TrackID, exp, g)
+			path = leveledStreamPath(trackUUID) + leveledQuery(g, token, exp)
+			mime = "audio/flac"
+			leveled = true
+			if req.Prerender {
+				h.leveled.Prerender(library.LeveledSource{
+					TrackID: req.TrackID, Path: track.FilePath, DurationMs: track.DurationMs,
+				}, g)
+			}
+		}
+	}
 
 	// Behind a TLS-terminating reverse proxy, r.TLS is nil even though
 	// the public-facing URL is https://. UPnP devices (Sonos especially)
@@ -131,18 +169,16 @@ func (h *handlers) handleCastStreamToken(w http.ResponseWriter, r *http.Request)
 	if h := r.Header.Get("X-Forwarded-Host"); h != "" {
 		host = h
 	}
-	// Include the file extension in the path so Sonos's URL probe sees a
+	// The path carries a file extension so Sonos's URL probe sees a
 	// recognizable audio file. Without it, Sonos reports TrackDuration=0
 	// and seeks past 0s land "after the end" -> early track-skip.
-	url := scheme + "://" + host + streamURLWithExt(trackUUID, extForFormat(track.FileFormat)) +
-		"?token=" + token + "&exp=" + strconv.FormatInt(exp, 10)
-
 	writeJSON(w, http.StatusOK, castTokenResponse{
-		Token: token,
-		Exp:   exp,
-		URL:   url,
-		MIME:  mimeForFormat(track.FileFormat),
-		Title: track.Title,
+		Token:   token,
+		Exp:     exp,
+		URL:     scheme + "://" + host + path,
+		MIME:    mime,
+		Title:   track.Title,
+		Leveled: leveled,
 	})
 }
 

internal/api/errors.go

@@ -3,7 +3,10 @@ package api
 import (
 	"encoding/json"
 	"log/slog"
+	"math"
 	"net/http"
+	"strconv"
+	"time"
 
 	"git.fabledsword.com/bvandeusen/minstrel/internal/apierror"
 )
@@ -36,6 +39,17 @@ func writeErr(w http.ResponseWriter, err error) {
 	}})
 }
 
+// writeRateLimited answers 429 with Retry-After in whole seconds, rounded
+// up so a client that honours it never arrives a moment early.
+func writeRateLimited(w http.ResponseWriter, wait time.Duration) {
+	secs := int(math.Ceil(wait.Seconds()))
+	if secs < 1 {
+		secs = 1
+	}
+	w.Header().Set("Retry-After", strconv.Itoa(secs))
+	writeErr(w, apierror.TooManyRequests("rate_limited", "too many attempts; try again later"))
+}
+
 // writeErrWithLog logs the error at Error level and writes the response.
 // Use for 500-class errors where the operator needs the cause in logs.
 func writeErrWithLog(w http.ResponseWriter, logger *slog.Logger, msg string, err error) {

internal/api/file_remove_error.go

@@ -0,0 +1,58 @@
+package api
+
+import (
+	"errors"
+	"fmt"
+	"log/slog"
+	"net/http"
+
+	"git.fabledsword.com/bvandeusen/minstrel/internal/apierror"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/library"
+)
+
+// fileRemoveAPIError answers a delete that could not reach the track's file
+// (#3918). Both delete endpoints use it, so the operator gets the same
+// explanation from the admin remove-track action and from quarantine's Delete
+// file.
+//
+// The unwritable case is a 409 rather than a 500 because nothing is broken: the
+// request conflicts with how the library is mounted, and the fix is the
+// operator's. The message names the directory — removal writes to the parent,
+// not the file — and the uid/gid the process runs as, which is the half of a
+// permission problem invisible from the host. Every case says nothing was
+// deleted, because that is exactly what the operator will be worried about.
+func fileRemoveAPIError(err error) (*apierror.Error, bool) {
+	var fre *library.FileRemoveError
+	if !errors.As(err, &fre) {
+		return nil, false
+	}
+	if fre.NotWritable() {
+		return &apierror.Error{
+			Status: http.StatusConflict,
+			Code:   "library_not_writable",
+			Message: fmt.Sprintf(
+				"Minstrel runs as uid %d, gid %d and cannot delete from %s (%s). "+
+					"The library mount must be writable by that user. Nothing was deleted.",
+				fre.UID, fre.GID, fre.Dir(), fre.Reason()),
+			Cause: err,
+		}, true
+	}
+	return &apierror.Error{
+		Status:  http.StatusInternalServerError,
+		Code:    "file_delete_failed",
+		Message: fmt.Sprintf("Could not delete %s (%s). Nothing was deleted.", fre.Path, fre.Reason()),
+		Cause:   err,
+	}, true
+}
+
+// logFileRemoveFailure records a delete that could not reach its file. An
+// unwritable library is an environment fact the operator can fix, so it is a
+// Warn; anything else is a real fault.
+func logFileRemoveFailure(logger *slog.Logger, apiErr *apierror.Error, attrs ...any) {
+	attrs = append(attrs, "code", apiErr.Code, "err", apiErr.Cause)
+	if apiErr.Status == http.StatusConflict {
+		logger.Warn("api: track file could not be deleted", attrs...)
+		return
+	}
+	logger.Error("api: track file could not be deleted", attrs...)
+}

internal/api/file_remove_error_test.go

@@ -0,0 +1,96 @@
+package api
+
+import (
+	"errors"
+	"fmt"
+	"io/fs"
+	"net/http"
+	"strings"
+	"syscall"
+	"testing"
+
+	"git.fabledsword.com/bvandeusen/minstrel/internal/library"
+)
+
+const removeTestPath = "/music/Moe Shop/WWW (2020)/01 - WWW.mp3"
+
+// removeFailure builds the error a delete service returns when the file would
+// not go, wrapped the way lidarrquarantine.DeleteFile and tracks.RemoveTrack
+// wrap it — the mapping has to see through that.
+func removeFailure(errno syscall.Errno) error {
+	return fmt.Errorf("delete file: %w", &library.FileRemoveError{
+		Path: removeTestPath, UID: 1000, GID: 1000,
+		Err: &fs.PathError{Op: "remove", Path: removeTestPath, Err: errno},
+	})
+}
+
+func TestFileRemoveAPIError(t *testing.T) {
+	cases := []struct {
+		name       string
+		errno      syscall.Errno
+		wantStatus int
+		wantCode   string
+		wantIn     []string
+	}{
+		{
+			name: "read-only mount", errno: syscall.EROFS,
+			wantStatus: http.StatusConflict, wantCode: "library_not_writable",
+			wantIn: []string{"uid 1000, gid 1000", "/music/Moe Shop/WWW (2020)", "read-only file system", "Nothing was deleted"},
+		},
+		{
+			name: "permission denied", errno: syscall.EACCES,
+			wantStatus: http.StatusConflict, wantCode: "library_not_writable",
+			wantIn: []string{"permission denied", "Nothing was deleted"},
+		},
+		{
+			name: "operation not permitted", errno: syscall.EPERM,
+			wantStatus: http.StatusConflict, wantCode: "library_not_writable",
+			wantIn: []string{"operation not permitted"},
+		},
+		{
+			name: "i/o error", errno: syscall.EIO,
+			wantStatus: http.StatusInternalServerError, wantCode: "file_delete_failed",
+			wantIn: []string{removeTestPath, "input/output error", "Nothing was deleted"},
+		},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			apiErr, ok := fileRemoveAPIError(removeFailure(tc.errno))
+			if !ok {
+				t.Fatal("a wrapped *library.FileRemoveError was not recognised")
+			}
+			if apiErr.Status != tc.wantStatus || apiErr.Code != tc.wantCode {
+				t.Fatalf("got %d %s, want %d %s", apiErr.Status, apiErr.Code, tc.wantStatus, tc.wantCode)
+			}
+			for _, want := range tc.wantIn {
+				if !strings.Contains(apiErr.Message, want) {
+					t.Errorf("message %q lacks %q", apiErr.Message, want)
+				}
+			}
+		})
+	}
+}
+
+// The unwritable answer must name the DIRECTORY. Removal needs write access to
+// the parent, so a message naming the file would send the operator to fix the
+// wrong permissions. The directory is a prefix of the file path, which is why a
+// plain "contains the directory" check could never catch that regression.
+func TestFileRemoveAPIError_NotWritableNamesTheDirectoryNotTheFile(t *testing.T) {
+	apiErr, _ := fileRemoveAPIError(removeFailure(syscall.EROFS))
+	if strings.Contains(apiErr.Message, "01 - WWW.mp3") {
+		t.Fatalf("message names the file rather than its directory: %q", apiErr.Message)
+	}
+}
+
+func TestFileRemoveAPIError_IgnoresOtherErrors(t *testing.T) {
+	for name, err := range map[string]error{
+		"nil":         nil,
+		"plain error": errors.New("delete track: connection reset"),
+		"path error":  &fs.PathError{Op: "remove", Path: removeTestPath, Err: syscall.EROFS},
+		"not found":   library.ErrTrackNotFound,
+	} {
+		if _, ok := fileRemoveAPIError(err); ok {
+			t.Errorf("%s: mapped as a file-remove failure", name)
+		}
+	}
+}

internal/api/leveled_stream.go

@@ -0,0 +1,168 @@
+package api
+
+import (
+	"context"
+	"crypto/hmac"
+	"crypto/sha256"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"net/http"
+	"os"
+	"strconv"
+	"time"
+
+	"github.com/go-chi/chi/v5"
+	"github.com/jackc/pgx/v5/pgtype"
+
+	"git.fabledsword.com/bvandeusen/minstrel/internal/apierror"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/auth"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/library"
+)
+
+// The leveled stream (M464 #5001): a track rendered with the user's loudness
+// gain applied, for the Sonos and UPnP speakers that fetch their own audio.
+// See internal/library/leveled.go for how it is rendered.
+
+// SignLeveledStreamToken signs a leveled stream URL. The gain is part of what
+// is signed, so a speaker's URL cannot be edited into a different render.
+// The message cannot collide with SignStreamToken's "<id>|<exp>": a plain
+// token does not open a leveled stream, nor the reverse.
+func SignLeveledStreamToken(secret []byte, trackID string, exp int64, g library.LeveledGain) string {
+	mac := hmac.New(sha256.New, secret)
+	lim := 0
+	if g.Limiter {
+		lim = 1
+	}
+	_, _ = fmt.Fprintf(mac, "%s|%d|leveled|%d|%d", trackID, exp, g.CentiDB, lim)
+	return hex.EncodeToString(mac.Sum(nil))
+}
+
+// VerifyLeveledStreamToken checks a token from SignLeveledStreamToken, and
+// that it has not expired.
+func VerifyLeveledStreamToken(secret []byte, trackID string, exp int64, g library.LeveledGain, token string) bool {
+	if time.Now().Unix() > exp {
+		return false
+	}
+	return hmac.Equal([]byte(SignLeveledStreamToken(secret, trackID, exp, g)), []byte(token))
+}
+
+// leveledStreamPath is the leveled stream's path. It ends in .flac because
+// Sonos reads the format from the URL's extension (task #610).
+func leveledStreamPath(trackID pgtype.UUID) string {
+	return "/api/tracks/" + uuidToString(trackID) + "/leveled.flac"
+}
+
+// leveledQuery is the query string a leveled URL carries.
+func leveledQuery(g library.LeveledGain, token string, exp int64) string {
+	lim := "0"
+	if g.Limiter {
+		lim = "1"
+	}
+	return "?g=" + strconv.Itoa(g.CentiDB) + "&lim=" + lim +
+		"&token=" + token + "&exp=" + strconv.FormatInt(exp, 10)
+}
+
+// leveledGainFor is the render request for one track under the user's
+// preference. Unity when leveling is off or the track is unmeasured, which
+// the caller answers with the plain stream.
+func (h *handlers) leveledGainFor(ctx context.Context, userID, trackID pgtype.UUID, asAlbum bool) (library.LeveledGain, error) {
+	q := dbq.New(h.pool)
+	prefs, err := library.LoadNormalizationPrefs(ctx, q, userID)
+	if err != nil {
+		return library.LeveledGain{}, err
+	}
+	gains, err := library.ReplayGainForTracks(ctx, q, []pgtype.UUID{trackID})
+	if err != nil {
+		return library.LeveledGain{}, err
+	}
+	return library.NewLeveledGain(library.LeveledGainDB(prefs, gains[trackID], asAlbum), prefs.Boost), nil
+}
+
+// parseLeveledGain reads ?g= and ?lim= from a leveled URL.
+func parseLeveledGain(r *http.Request) (library.LeveledGain, bool) {
+	c, err := strconv.Atoi(r.URL.Query().Get("g"))
+	if err != nil {
+		return library.LeveledGain{}, false
+	}
+	lim := r.URL.Query().Get("lim")
+	if lim != "0" && lim != "1" {
+		return library.LeveledGain{}, false
+	}
+	g := library.LeveledGain{CentiDB: c, Limiter: lim == "1"}
+	return g, g.Valid()
+}
+
+// handleGetLeveledStream implements GET /api/tracks/{id}/leveled.flac. It
+// accepts a session, like the plain stream, or a leveled token: the gain in
+// the query must be the one the token was signed for.
+func (h *handlers) handleGetLeveledStream(w http.ResponseWriter, r *http.Request) {
+	rawID := chi.URLParam(r, "id")
+	g, ok := parseLeveledGain(r)
+	if !h.leveledAuthOk(r, rawID, g, ok) {
+		writeErr(w, apierror.ErrUnauthorized)
+		return
+	}
+	if !ok {
+		writeErr(w, apierror.BadRequest("invalid_gain", "g and lim must describe a valid gain"))
+		return
+	}
+	if h.leveled == nil {
+		writeErr(w, &apierror.Error{Status: http.StatusServiceUnavailable, Code: "leveling_unavailable",
+			Message: "leveled streams are not available on this server"})
+		return
+	}
+	track, apiErr := resolveByID(r, "id", dbq.New(h.pool).GetTrackByID, "track")
+	if apiErr != nil {
+		writeErr(w, apiErr)
+		return
+	}
+	path, err := h.leveled.Path(r.Context(), library.LeveledSource{
+		TrackID: rawID, Path: track.FilePath, DurationMs: track.DurationMs,
+	}, g)
+	switch {
+	case errors.Is(err, library.ErrLeveledSourceMissing):
+		writeErr(w, &apierror.Error{Status: http.StatusNotFound, Code: "not_found", Message: "track file not found"})
+		return
+	case r.Context().Err() != nil:
+		return // the speaker hung up; the render carries on for its retry
+	case err != nil:
+		writeErrWithLog(w, h.logger, "leveled stream: render failed", apierror.InternalMsg("render failed", err))
+		return
+	}
+	f, err := os.Open(path)
+	if err != nil {
+		// Evicted between render and open: rare, and the speaker retries.
+		writeErrWithLog(w, h.logger, "leveled stream: open render", apierror.InternalMsg("server error", err))
+		return
+	}
+	defer func() { _ = f.Close() }()
+	info, err := f.Stat()
+	if err != nil {
+		writeErrWithLog(w, h.logger, "leveled stream: stat render", apierror.InternalMsg("server error", err))
+		return
+	}
+	w.Header().Set("Content-Type", "audio/flac")
+	w.Header().Set("Accept-Ranges", "bytes")
+	w.Header().Set("Cache-Control", "private, max-age=86400")
+	http.ServeContent(w, r, "leveled.flac", info.ModTime(), f)
+}
+
+// leveledAuthOk mirrors streamAuthOk: a session, or a token signed over this
+// track and this gain. A malformed gain fails the token path, since there is
+// nothing it could have been signed over.
+func (h *handlers) leveledAuthOk(r *http.Request, trackID string, g library.LeveledGain, gainOK bool) bool {
+	if _, ok := auth.UserFromContext(r.Context()); ok {
+		return true
+	}
+	if !gainOK {
+		return false
+	}
+	tok := r.URL.Query().Get("token")
+	exp, err := strconv.ParseInt(r.URL.Query().Get("exp"), 10, 64)
+	if tok == "" || err != nil {
+		return false
+	}
+	return VerifyLeveledStreamToken(h.streamSecret, trackID, exp, g, tok)
+}