feat: the extension adds Discord channels to an artist you pick, and its tests gate the XPI (milestone 429)

Server (#4420)
- extension_service gains a Discord pattern (server or channel, jump links,
  ptb/canary; not DMs or threads), mirrored in platforms.js and pinned by
  the shared artist-url-samples.json.
- probe on a Discord URL matches the source by ids under any artist, reports
  a whole-server source as covering the channel, suggests the artist who owns
  another source on the same server, and names server/channel via the stored
  token (best-effort, bounded, no rate-limit waits).
- quick-add takes artist_id / artist_name; Discord URLs are stored canonical.

Extension (#4421, #4422)
- Content script on discord.com; SPA navigation by URL polling (the old
  pushState patch ran in the isolated world and never fired); stale probes
  are dropped.
- Discord chip opens an Add panel: this channel or the whole server, and the
  suggested artist / a search / a new name.
- Popup: sources show artist, platform and state; a Discord token export is
  verified by FC and the result shown. Token capture covers ptb/canary.
- Pure logic in lib/chip.js and lib/popup-format.js, with specs.

CI (#4423)
- extension.yml's lane (web-ext lint, vitest, XPI contents) moves into
  build.yml as extension-test and joins the needs of sign-extension,
  build-web and build-agent. As a separate workflow it gated nothing: a red
  extension suite still signed and shipped the XPI (rule 177).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LVjrnpQjRgHdvq95rASoiR

.forgejo/workflows/build.yml

@@ -242,7 +242,7 @@ jobs:
   # rather than left running beside the new mechanism (rule 22).
   #
   # Two things are still worth asserting, and this is the only lane that can:
-  # the extension.yml suite runs on node:24-slim, which is exactly why
+  # the extension-test lane runs on node:24-slim, which is exactly why
   # version.spec.js sticks to packaging.sh's git-free subcommands.
   #   1. the derivation actually resolves on this commit
   #   2. the derived string is one AMO will accept, checked against Mozilla's
@@ -378,6 +378,76 @@ jobs:
       - run: npm run test:unit
       - run: npm run build
 
+  # The extension's lane: web-ext lint, the vitest suite, and the check that
+  # asks web-ext what it ACTUALLY packaged. Moved in from `extension.yml`
+  # (deleted) at milestone 429 — the same move `ci.yml` made on 2026-09-23 and
+  # for the same reason: a separate workflow cannot gate this one, so a red
+  # extension suite still let `sign-extension` sign and `build-web` ship the
+  # XPI. It is a lane in THE GATE now. Its old path filter is gone with it; a
+  # filter here would make the lane skip, and a skipped lane blocks the publish.
+  #
+  # The vitest suite is also the JS half of the #3093 artist-pattern mirror —
+  # the Python half runs in backend-lint-and-test — so until this move one half
+  # of that guard could fail without stopping anything.
+  extension-test:
+    runs-on: python-ci
+    container:
+      image: node:24-bookworm-slim
+    steps:
+      - uses: actions/checkout@v4
+      # Not --no-save: vitest and web-ext are both real devDependencies now,
+      # and the suite needs vitest resolvable from node_modules.
+      - name: Install dev dependencies
+        run: cd extension && npm install --no-audit --no-fund
+      - name: Lint
+        run: cd extension && npm run lint
+      # Pure-logic specs over lib/url.js and lib/platforms.js plus manifest /
+      # package version-consistency checks. No browser, no network.
+      - name: Unit tests
+        run: cd extension && npm run test:unit
+
+      # Everything else about packaging is asserted against our own declaration
+      # of what ships. This is the only check that asks web-ext what it ACTUALLY
+      # put in the archive. Until now that was an unverified assumption about
+      # glob semantics — and a fragile one: `test/**` reaches web-ext intact
+      # only because callers `set -f` first, so losing that quoting would
+      # silently start shipping dev files with no other signal.
+      - name: Verify XPI contents
+        run: |
+          set -eu
+          command -v unzip >/dev/null 2>&1 || { apt-get update -qq && apt-get install -y -qq unzip; }
+          cd extension
+          npm run build
+          ZIP=$(ls web-ext-artifacts/*.zip | head -1)
+          echo "=== packaged entries in $ZIP ==="
+          unzip -Z1 "$ZIP" | sort
+          echo "=== end ==="
+          ENTRIES=$(unzip -Z1 "$ZIP")
+          fail=0
+          # Must NOT ship: repo infrastructure with no business in a user's browser.
+          for pat in 'test/' 'scripts/' 'vitest.config.js' 'package.json' 'package-lock.json' 'README.md' 'node_modules/' 'web-ext-artifacts/'; do
+            if echo "$ENTRIES" | grep -q "^$pat"; then
+              echo "ERROR: '$pat' was packaged into the XPI but must not be"
+              fail=1
+            fi
+          done
+          # Must ship: if an exclusion pattern ever over-matches, the extension
+          # breaks at runtime rather than at build time, so assert presence too.
+          for req in 'manifest.json' 'lib/url.js' 'lib/api.js' 'lib/platforms.js' 'lib/cookies.js' 'lib/chip.js' 'lib/popup-format.js'; do
+            if ! echo "$ENTRIES" | grep -q "^$req$"; then
+              echo "ERROR: '$req' is missing from the XPI"
+              fail=1
+            fi
+          done
+          for dir in 'background/' 'popup/' 'options/' 'content/' 'icons/'; do
+            if ! echo "$ENTRIES" | grep -q "^$dir"; then
+              echo "ERROR: nothing from '$dir' was packaged"
+              fail=1
+            fi
+          done
+          [ "$fail" -eq 0 ] || exit 1
+          echo "XPI contents verified."
+
   # Single integration job — collapsed from a 3-way shard split on 2026-06-04.
   # The shards existed to parallelize ~8.5min of integration tests; once the
   # throwaway Postgres runs with fsync OFF (the durability step below) the whole
@@ -521,7 +591,8 @@ jobs:
     # itself through a job-level `if:` that could not read `env`, and a design
     # where only a FAILED gate blocks would have published unverified images
     # while reporting success.
-    needs: [lint, extension-version, backend-lint-and-test, frontend-build, integration]
+    needs: [lint, extension-version, backend-lint-and-test, frontend-build, extension-test,
+            integration]
     # A pull_request run is the lanes and nothing else. This is the ONLY thing
     # separating "validate a Renovate bump" from "publish a Renovate bump", so
     # it is stated on each publishing job rather than inferred from a `needs`
@@ -859,7 +930,7 @@ jobs:
     # default behaviour is exactly what we want: a failed sign skips build-web
     # rather than shipping an image without its XPI.
     needs: [sign-extension, lint, extension-version, backend-lint-and-test,
-            frontend-build, integration]
+            frontend-build, extension-test, integration]
     # The lanes in that list are THE GATE (2026-09-23) — see sign-extension's
     # copy of this comment for why, including the property that a SKIPPED lane
     # blocks as firmly as a failing one. They are repeated here rather than
@@ -2083,7 +2154,8 @@ jobs:
     # itself through a job-level `if:` that could not read `env`, and a design
     # where only a FAILED gate blocks would have published unverified images
     # while reporting success.
-    needs: [lint, extension-version, backend-lint-and-test, frontend-build, integration]
+    needs: [lint, extension-version, backend-lint-and-test, frontend-build, extension-test,
+            integration]
     # What `promote` needs to publish this image once the smoke has passed:
     # the manifest this run built (empty on a reuse hit) and every tag it
     # belongs under. Same meaning as build-web's outputs of the same names.