New package internal/sync. LogChange writes a library_changes row inside
the supplied tx. Encode helpers produce stable composite ids for like_*
and playlist_track entries. Subsequent commits wire LogChange into the
scanner / likes / playlists services.
Also: dbtest.dataTables now includes library_changes so test isolation
holds across runs.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Append-only change log for library entities. Every mutation on
artists/albums/tracks/likes/playlists/playlist_tracks will write a row
in the same transaction as the mutation itself (wired in subsequent
commits). Powers the Flutter delta-sync endpoint (#357).
- 0025_library_changes migration (up + down)
- internal/db/queries/library_changes.sql (Insert, GetSince, MaxCursor, MinCursor)
- regenerated dbq from sqlc
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
- Updates the happy-path test stub to handle the three list endpoints
Lidarr exposes (qualityprofile / metadataprofile / rootfolder) and
asserts profiles + folders make it through to the response.
- Adds a partial-failure case where one list endpoint 5xxs; verifies
ok=true, the failing list is omitted, and list_errors carries its
bucket code.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Extends POST /api/admin/lidarr/test response to include quality_profiles,
metadata_profiles, root_folders, and an optional list_errors map when the
Lidarr connection succeeds. The three list fetches run in parallel after
the ping; any per-list failure goes into list_errors so the response can
still report ok=true with whatever data did come back. Failed-ping
response shape is unchanged.
This lets /admin/integrations populate its dropdowns on a single
round-trip during first-time setup, fixing the chicken-and-egg where
the dropdowns previously gated on cfg.Enabled (which can't be true
until the first save, which itself needs non-zero defaults).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
The bootstrap-admin-from-env-vars flow was a holdover from before
self-registration could create the first admin. Now that handleRegister
+ CreateUserFirstAdminRace promotes the first user to register on an
empty users table (verified shipped in v2026.05.08.2 / #376), the
bootstrap path is just a second source of truth that confuses operators
(and leaves an "admin" account in the DB that nobody asked for).
Removes:
- internal/auth/bootstrap.go + its test
- The auth.Bootstrap call from cmd/minstrel/main.go
- AuthConfig + AdminBootstrapConfig structs from config
- MINSTREL_AUTH_ADMIN_USERNAME / _PASSWORD env reads + their test
- The auth: block from config.example.yaml
- Bootstrap-related comments in docker-compose.yml + README.md
The README quickstart now points operators at /register on first start
instead of "watch the logs for a one-time password."
Existing instances keep their bootstrap-admin row in the DB; operators
who want it gone can register a new admin via /register, promote them
in /admin/users, then delete the old bootstrap user (last-admin guard
will require the new admin to be promoted first). No migration needed.
Recovery story for forgotten admin passwords now hinges on Fable #321
(admin password reset CLI) — currently the only path back in if no
other admin exists.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Add audit.WriteOrLog: a one-line wrapper around Write that logs at
Warn and swallows the error, matching the package contract that
audit failures must not break user-facing operations.
Migrate the 13 call sites across 7 files in internal/api/ from the
3-line "if err != nil { logger.Warn(...) }" shape to a single call.
audit.Write stays exported for tests + any future caller that
needs strict semantics.
Adds three tests: success (no log), failure-via-closed-pool (Warn
record with action+err keys), and nil-logger (no panic). Tests
skip when MINSTREL_TEST_DATABASE_URL is unset, matching the
existing harness convention.
The PR1-T2 admin handler migration replaced bespoke 500-class messages
("lookup failed", "refetch failed", "trigger failed", "bump failed",
"remove failed", "update failed", "schedule row missing", "re-read
failed", "read failed") with apierror.Internal(err), which forces the
wire Message to "internal server error". That violates the PR1
contract that errEnvelope{Code, Message} must remain byte-identical
for existing clients.
Add apierror.InternalMsg(message, cause) — a 500-class constructor
that preserves the call site's user-facing message while keeping the
cause attached for logging and errors.Is. Re-migrate the 12 admin
sites whose pre-1cc7eb6 source had a non-empty bespoke Message so
they restore the original wire string. Sites whose original Message
was empty stay on Internal(err) (humanization to "internal server
error" is a tolerable improvement, not a regression).
admin_smtp.go's send_failed site (line 129) was already preserved
via a raw &apierror.Error literal in 1cc7eb6 and needs no fix.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Rewrite writeErr(w, err) to wrap *apierror.Error via apierror.From,
preserving the existing {"error": {"code", "message"}} wire envelope.
Add writeErrWithLog helper for 500-class errors that need an operator
log line. Migrate all 13 admin_*.go handler files (~76 call sites) to
the new signature; T3 will sweep the remaining api package.
The old 4-arg writeErr is removed, so non-admin call sites in
internal/api will not compile until T3 lands. This is by design — T2
and T3 are paired.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Wires the auto_approve_requests user flag into the request creation
flow. When the flag is set (admin enabled it via /admin/users from
U2-T3), POST /api/requests transitions the just-created pending row
through Service.Approve inline, which dispatches to Lidarr the same
way a manual admin approve does.
Failures inside Approve (ErrLidarrDisabled, ErrDefaultsIncomplete,
network/Lidarr errors) leave the row pending — same fallback as
manual approve hitting the same path. The user gets a 201 either
way; admin can still resolve the row in /admin/requests if it
stayed pending. The handler logs the auto-approve failure with
user_id + request_id for observability.
The "actor" id passed to Approve is the user's own ID — they're
acting under the privilege the admin granted them via the toggle.
The trail of "admin set the flag" already lives in audit_log
(ActionAutoApproveToggle from U2-T2). Adding a per-auto-approval
audit entry is a future enhancement; for v1 the toggle audit plus
the request row's status transition is enough.
Test verifies the Lidarr-disabled fallback contract: a user with
auto_approve=true and Lidarr unavailable still gets 201 Created
with status=pending (no crash, no 500). The "auto-approve actually
succeeds" test path requires a Lidarr stub; deferred until a
broader Lidarr test fixture lands.
Two real algorithm bugs in F-T1's For-You composition + Discover
allocator. Both surfaced as failing unit tests under go test -race.
1. redistributeSlots was re-redistributing a bucket's full deficit
on every pass instead of just the residual. The loop computed
`deficit = b.want - final[i]` each iteration, but final[i] for
a deficit bucket never increases (its supply is exhausted), so
pass N saw the same deficit as pass N-1 and kept shoveling it
to peers. For [want:40 avail:100, want:30 avail:0, want:30 avail:100],
four passes pushed cross-user's deficit into dormant+random four
times each, hitting the 100-slot clamp at the end and producing
[50, 0, 50] instead of the spec'd [55, 0, 45].
Fix: track per-source `redistributed[i]` and subtract it from the
deficit each pass. Multi-pass behavior still works for the case
where a peer's supply runs out mid-distribution.
2. tieBreakHash used FNV-1a 64-bit with trackID + dateStr appended.
For dateStrs differing only in the last character ("2026-05-07"
vs "2026-05-08"), the FNV state diverged only in low bits at the
final byte; multiplication by FNV_prime propagates upward but the
relative ordering of 60 small candidate UUIDs (which differ only
in their last byte) ended up identical across the two dates. The
For-You head/tail test asserted that the tail's first 5 should
change across days; it didn't.
Fix: switch to SHA-256 truncated to 8 bytes. SHA-256 has full
avalanche, so any single-bit input change roughly half-flips the
output bits and meaningfully reorders.
The hash isn't security-load-bearing; we just need strong avalanche
for tiny dateStr deltas. Determinism (same inputs → same output) is
preserved.
Three Go lint hits + two web test failures, all from the U3 push.
- internal/mailer/mailer.go: SentEmail.HtmlBody → HTMLBody (Go's
initialism convention; revive flagged); FakeSender.Send unused
ctx parameter renamed to _.
- internal/audit/audit_test.go: removed dead validUUID helper. It
was added speculatively in U1-T1 and never called by any test.
pgtype import stays — other tests use it.
- web/src/routes/settings/settings.test.ts: existing ListenBrainz
tests queried `getByRole('button', { name: /save/i })` which
worked when the page had only one Save button. The new Profile
card adds a "Save profile" button that also matches the regex,
triggering "found multiple elements". Anchored to /^save$/i for
exact-match. The newer Save profile tests still use
/save profile/i which is unique.
This is the same shape of test-fixture-lag I owe an answer for: I
landed new content that broke an existing test, and the existing
test had a too-loose selector. The right fix is to tighten the old
selector now (this commit) and to flag this pattern — selectors
that regex-match by partial words — as a candidate for the DRY
pass / test-utils consolidation.
Five fixes in one commit, all from the U1+U2+U3 push:
1. internal/api/library_test.go's Mount call wasn't updated when
U3-T4 added the mailer.Sender param. 17 args, sig wants 18.
Adds a trailing nil for the mailer. Same shape of test-fixture
lag the project has hit before — flagged as a recurring pattern
for the DRY-pass slice.
2. web/src/routes/settings/settings.test.ts mocked $lib/api/me with
`getAPIToken: vi.fn()` (no return value). The new /settings API
Token card's $effect calls `getAPIToken().then(...)` which threw
"Cannot read properties of undefined (reading 'then')" on every
ListenBrainz test. Default the mock to mockResolvedValue so any
test that doesn't override gets a valid resolution.
3. web/src/routes/admin/users/users.test.ts queried row buttons by
/^Delete$/ but T3 added per-user aria-labels ("Delete alice"),
so the row buttons' accessible name is no longer "Delete". The
modal's confirm button has no aria-label so its name IS "Delete"
exactly. Tests now click by per-user aria-label first, then by
/^Delete$/ for the modal confirm.
4. Same file: /Set password/i regex matched both the dialog's
submit button AND the row's "Reset password for ..." buttons
(because regex `Set` matches "ReSet" case-insensitively). Switched
to /^Set password$/ exact-match.
5. web/src/routes/reset-password/[token]/reset-password.test.ts had
/New password/i which matched both the "New password" and
"Confirm new password" labels. Switched to exact-match string
selectors.
6. web/src/routes/forgot-password/+page.svelte's onSubmit handler
had no catch — a rejected forgotPassword() bubbled as an
unhandled rejection in vitest. Added a silent catch since the
page intentionally shows the same success message regardless of
outcome (no-enumeration posture).
Three CI fixes from the U1+U2+U3 push:
- internal/api/admin_users.go imported the standalone
github.com/jackc/pgconn — that module isn't in go.sum and
go vet caught it. Switch to github.com/jackc/pgx/v5/pgconn
(the path used elsewhere in the package, e.g. auth_register.go
and me_profile.go).
- /reset-password/[token] dereferenced page.params.token without
the undefined narrowing svelte-kit's typegen requires. Coalesce
to '' on read and reject empty token at submit time with a
clear error.
- /admin/integrations SMTP card had a label without an associated
control as the TLS row's leading column header. Switched to a
span — the actual checkbox lives in the wrapping label below it.
POST /api/auth/forgot-password and POST /api/auth/reset-password.
Forgot-password ALWAYS returns 200 with empty JSON to prevent
enumeration of registered emails. Side effect: when email matches
a user with email-on-file, generates a 32-byte hex token (24h
TTL), inserts into password_resets, and sends the reset email via
the mailer. Mailer failures are logged (not surfaced) and the
audit log carries metadata.email_match for operator visibility.
Reset-password atomically claims the token via UsePasswordReset
(:execrows; concurrent calls can't both succeed). On rows=1,
hashes the new password and writes via ChangeUserPassword.
Returns 204 on success, 400 invalid_token on stale/used/missing
tokens, 400 password_too_short for short passwords. Audits
ActionPasswordResetByEmail.
Wires the mailer.Sender into the handlers struct via Mount;
production sender (NewSMTPSender) constructed in server.Router();
tests inject FakeSender via testHandlers default. The reset
URL embedded in the email is derived from r.Host (no PublicURL
config setting in v1; self-hosted operators see their own
hostname).
Tests cover happy-path send + token-row insertion, unknown email
returns 200 with no send, mailer failure still returns 200, reset
happy path verifies bcrypt match + used_at set, already-used
token 400, expired token 400, short password 400, bogus token 400.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
New internal/mailer/ package:
- Sender interface with two impls: SMTPSender (production, reads
smtp_config at send time so admin edits apply without restart;
uses stdlib net/smtp + STARTTLS) and FakeSender (test/concurrent-
safe call recorder).
- Embedded text + HTML templates for the password reset email,
rendered via stdlib text/template + html/template. The HTML
uses the FabledSword forest-teal accent color.
- ErrNotConfigured surfaces when smtp_config.enabled is false or
required fields are empty; callers like the future forgot-password
handler will treat this as "log and pretend success" to avoid
user-enumeration leaks.
Three admin endpoints under RequireAdmin:
- GET /api/admin/smtp-config — returns the singleton; password
field is masked ("***" or "").
- PUT /api/admin/smtp-config — updates settings. Validates
host + from_address are non-empty when enabled=true. Empty
password in the request preserves the stored value (so the
operator doesn't have to re-enter it on every save).
- POST /api/admin/smtp-config/test — sends a real test email to
the calling admin's email. 400 if admin has no email; 500 with
the error message on send failure (so the operator can debug
config without grep-then-trace through logs).
Tests cover the password-mask, password-preservation-on-empty,
enabled-requires-host-and-from validation, and the no-email-on-file
rejection. Mailer unit tests cover the fake recorder and template
rendering. The "real SMTP send" path needs a live server and isn't
covered in CI; the FakeSender covers that role for downstream tests.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Four authenticated endpoints for the user's own account:
- PUT /api/me/password — change own password. Caller must
supply current_password (verified via bcrypt). Distinct from
admin-driven reset (which doesn't require knowing the old).
Audits ActionPasswordChangeSelf.
- PUT /api/me/profile — set display_name + email. Both fields
are nullable; empty string clears, omitted leaves unchanged.
Email is lowercased before store + format-validated. Unique
violation → 409 email_taken.
- GET /api/me/api-token — returns current API token (for
copy-paste into Subsonic clients).
- POST /api/me/api-token — regenerates token. Old one stops
working immediately. Audits ActionTokenRegenerate.
All four use the existing RequireUser middleware on the authed
sub-router; audit writes are best-effort (logged on failure).
Tests cover happy paths, wrong-password 401, password-too-short
400, email-invalid 400, email-taken 409, clear-by-empty-string,
omit-leaves-unchanged, token GET + regen.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Adds users.email (optional, lowercase-unique via partial index),
smtp_config singleton, and password_resets tokens. Plus the
queries U3-T2 / T3 / T4 use:
- ChangeUserPassword: self-service password change. HTTP layer
verifies the current password before this fires.
- UpdateUserProfile: set display_name + email together.
- RegenerateApiToken: invalidate old API token.
- GetUserByEmail: case-insensitive lookup for forgot-password.
- GetSMTPConfig + UpdateSMTPConfig: admin SMTP settings CRUD.
- CreatePasswordReset / GetPasswordReset / UsePasswordReset
(:execrows for atomic claim) / DeleteExpiredPasswordResets
(cron-style cleanup, not yet wired).
Email column is nullable; users without email have admin-reset
as their only password-recovery path. The lower() unique index
allows many NULLs and prevents case-insensitive duplicates.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Four new admin endpoints under existing RequireAdmin middleware:
- POST /api/admin/users — admin-creates-user. Body
{username, password, display_name?, is_admin?}. Same username
+ password validation as the public /register handler. 409
on duplicate. Audits ActionCreateUserAdmin.
- DELETE /api/admin/users/{id} — hard delete. Last-admin guard
refuses delete when target is the only admin (409). Schema's
ON DELETE CASCADE on user-FK tables handles plays/likes/
sessions cleanup. Audits ActionDeleteUser with target's
username + was_admin flag.
- POST /api/admin/users/{id}/reset-password — body
{password}. 8-char minimum. Admin sets a new password
without knowing the old one. Audits ActionPasswordResetAdmin.
- PUT /api/admin/users/{id}/auto-approve — body
{auto_approve: bool}. Toggles the per-user flag added in T1
(the #355 sub-feature surface). Audits ActionAutoApproveToggle.
adminUserView shape extended with auto_approve_requests so the
list and toggle responses carry the flag. ListUsers SQL query
updated to include auto_approve_requests; generated Go updated
to match. Tests cover happy paths, last-admin guard on delete,
password validation, duplicate username, and the auto-approve
round-trip.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Adds users.auto_approve_requests boolean default false (the #355
sub-feature surface; the request-flow handler that honors this
flag is U2.5 follow-up work).
Four new sqlc queries for the U2 admin endpoints:
- CreateUserAdmin: admin-driven user creation, accepts all five
fields explicitly.
- DeleteUser: hard delete; schema's ON DELETE CASCADE foreign
keys handle plays/likes/sessions cleanup. Last-admin guard
lives in the HTTP layer (next task).
- ResetUserPassword: admin sets a new hashed password without
knowing the old one.
- UpdateUserAutoApprove: toggles the new boolean.
Self-service equivalents (knows-current-password change, etc.)
are U3 work and use distinct queries.
Five admin endpoints under existing RequireAdmin middleware:
- GET /api/admin/invites — list active + recently-redeemed
- POST /api/admin/invites — generate 24h invite, returns
{token, expires_at, ...}. Audits ActionInviteCreate.
- DELETE /api/admin/invites/{token} — revoke unredeemed invite.
Audits ActionInviteRevoke.
- GET /api/admin/users — list all users (id, username,
display_name, is_admin, created_at).
- PUT /api/admin/users/{id}/admin — toggle is_admin with
last-admin guard. Audits ActionPromoteAdmin / ActionDemoteAdmin.
Last-admin guard counts admins, refuses demotion of the sole
admin with 409 'last_admin'. Race window between count and update
is acceptable for v1 — worst case is 'no admins left,' which the
env-driven bootstrap or CLI reset can recover from. Common path
('admin demotes themselves') is now blocked.
Adds ListUsers, CountAdmins, UpdateUserAdmin sqlc queries to
users.sql.
Tests cover: invite create/list/delete round-trip, non-admin gets
403, user list, promote happy path, last-admin demotion refused,
two-admins demotion allowed.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
POST /api/auth/register accepts {username, password, invite_token?,
display_name?} and creates a user. Race-safe first-admin path: when
the users table is empty, the SQL query (CreateUserFirstAdminRace)
inserts is_admin computed from a SELECT NOT EXISTS subquery — no
serializable isolation needed; concurrent empty-state registrations
both end up admin (benign).
Past first-admin, registration_settings.mode dictates: 'invite_only'
(default) requires a valid unredeemed unexpired invite token, which
is atomically claimed via RedeemInvite (rows-affected returns from
sqlc's :execrows directive). 'open' mode skips the invite check.
On success: hashes password (bcrypt), mints session token + cookie
matching handleLogin's shape, mints a separate api_token for
Subsonic clients, audits ActionRegister + ActionInviteRedeem
(best-effort — a failed audit write does NOT fail the user-facing
operation).
Validation: 3-32 char usernames (alphanumeric + underscore +
hyphen), 8-char minimum password. Duplicate username surfaces as
409.
Tests cover: first-user-becomes-admin, invite-only requires token,
valid token redeems + non-admin role, invalid token 400, open mode
skips check, duplicate username 409, password too short 400,
username format 400, race scenario asserts at-least-one-admin.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Schema for user management U1: display_name on users; user_invites;
registration_settings singleton (default 'invite_only'); audit_log.
Plus the internal/audit package centralizing the action-name
vocabulary and JSON metadata marshaling so handlers don't repeat
boilerplate.
Race-safe first-admin uses a query-shape primitive
(CreateUserFirstAdminRace's WHERE NOT EXISTS subquery) rather than
a schema-level constraint. Concurrent empty-state registrations
both see 'no users yet' and both insert as admin — fine, having
two admins from the start is benign; what matters is at-least-one.
users.username uniqueness arbitrates if the two callers picked the
same username.
CreateUser signature gains display_name (nullable); existing
bootstrap call sites pass nil. The audit package declares the full
U1+U2+U3 action vocabulary upfront so subsequent slices are purely
additive on the caller side.
Tests cover audit Write with + without metadata and that every
declared action constant persists correctly.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
POST /api/playlists/system/for-you/refresh re-runs the system
playlist build synchronously for the calling user, then returns
the freshly-built For-You playlist's id, track count, and the
track IDs in playlist position order.
The frontend tile play button (next task) calls this endpoint
on click and enqueues the returned track_ids directly — one
roundtrip, no follow-up "list tracks" call needed for playback
to start. Same authenticated-user-only posture as the Discover
refresh from D-T3.
Returns playlist_id=null and track_ids=[] when the build
succeeded but the user's library yielded no eligible candidates
(degenerate empty-library). Returns 500 on actual build failure.
Tests cover 200 with shape (track_count matches len(track_ids))
and 401 without auth.
Two improvements to the system playlist builder:
1. Per-artist (<=3) and per-album (<=2) caps applied to the
pickTopN truncation step, using the same numeric caps Discover
already enforces. Both For-You and Songs-like-X benefit. Same
skewed candidate pool no longer collapses to "10 tracks from
the same artist" — the playlist always carries at least 9
distinct artists in 25 slots.
2. New pickHeadAndTail function for For-You: 20 top-similarity
tracks + 5 sampled from the tail (positions 2*headN onward of
the score-sorted, cap-applied pool). Tail sampling uses
tieBreakHash for daily determinism — same user same day still
sees the same playlist, but the daily refresh feels less
stuck-in-a-rut. Tail tracks are still similarity-related
(they passed the similarity candidate filter) so the user
should enjoy them, just from artists they wouldn't have surfaced
via strict top-N ranking.
Songs-like-X keeps the simple pickTopN call — the seed-artist
context already provides the "you'll like this" framing without
needing a tail injection.
Refactors pickTopN internals: now sorts candidates first via
scoreAndSortCandidates, applies the cap on []Candidate via
capCandidatesByAlbumAndArtist, and truncates. Removes the now-
dead stableSortByScoreThenHash helper (only used in old pickTopN).
The cap helper mirrors capByAlbumAndArtist in discover.go but
operates on recommendation.Candidate so it sees Track.AlbumID /
Track.ArtistID directly.
Tests cover the cap helper truth table, head+tail split with
small/large pools, buffer-zone exclusion, daily determinism, and
cross-day tail variance.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
The collage builder pulled exactly 4 tracks (in playlist position
order) and rendered each track's album cover into a 2x2 cell. A
playlist where the first 4 tracks share an album rendered as four
identical cells of the same cover; a "Songs like X" mix where two
similar artists dominated produced very similar collages.
Now pulls 50 rows from the same query and drops adjacent /
duplicate covers in Go before passing to the renderer. NULL and
empty cover_art_paths are NOT deduped (they each render the
fallback glyph in their own cell — the right behavior for a
partially-covered playlist).
Preserves playlist position order: the first occurrence of each
unique cover wins. Five unit tests cover the behavior: drops
duplicates, keeps NULLs, handles empty-string paths, preserves
order, mixed null/dup case.
Tangential to the For-You CTA slice but lands here as a small
quality-of-life fix that benefits every playlist's collage.
POST /api/playlists/system/discover/refresh re-runs the system
playlist build synchronously for the calling user, then returns
their newly-built Discover playlist's UUID and track count.
Used by the frontend's "Refresh" affordances (next task) on the
Discover detail page header and the home Playlists row tile kebab.
Operator's escape hatch when they want a different randomness
without waiting for tomorrow's cron tick (e.g., after pasting a
Last.fm key, after the daily cover-art enrichment expanded their
playable library, or just for the heck of it).
Authenticated user only; the authed sub-router's RequireUser
middleware handles 401. Each user refreshes only their own
Discover — no admin route, no cross-user impersonation.
Adds GetSystemPlaylistByVariantForUser sqlc query for the response
lookup. Returns playlist_id=null and track_count=0 if the build
succeeded but the user's library yielded no eligible tracks
(degenerate empty-library).
bvandeusen