feat(enrichment): record status/errors and trust high-confidence AcoustID

Two related gaps surfaced from "uploaded a track, nothing changed / no status":

- A track could stay stuck on `pending` forever (an unexpected worker error
  rolled back the run without recording anything), and `failed` carried no
  reason. Add `tracks.metadata_error` + `tracks.enriched_at` (migration), stamp
  the outcome in apply_enrichment, add TrackRepository.mark_enrichment_failed,
  wrap enrich_task to persist crashes as `failed` in a fresh session, and emit a
  human-readable no-match reason. Expose metadata_error/enriched_at in TrackOut.

- The tag-first merge let junk embedded tags (e.g. "Music Track"/"Sound_13958")
  override even a 0.99-confidence AcoustID match. Add acoustid_trust_score
  (default 0.85): above it the acoustic identity wins for title/artist/album/
  year, tags are fallback; below it, tag-first as before.

Add a license-free real-file fixture (Scarlet Fire / Otis McDonald) whose junk
tags AcoustID overrides, with an always-on tag-reader test plus fpcalc/AcoustID/
network-gated identity + full-pipeline tests (skip on host, run in the container).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/infrastructure/db/models/track.py

@@ -6,9 +6,10 @@
 imports/downloads stay idempotent (plan §4, §6.1).
 """
 
+import datetime as dt
 import uuid
 
-from sqlalchemy import ForeignKey, Integer, String, UniqueConstraint
+from sqlalchemy import DateTime, ForeignKey, Integer, String, UniqueConstraint
 from sqlalchemy.orm import Mapped, mapped_column
 
 from app.infrastructure.db.base import Base
@@ -63,6 +64,16 @@ class TrackModel(UUIDPrimaryKeyMixin, TimestampMixin, Base):
         nullable=False,
         default=MetadataStatus.PENDING.value,
     )
+    # Human-readable reason the last enrichment run set ``failed`` (no match, or
+    # an unexpected worker error). ``None`` once a run succeeds. Surfaced in the
+    # UI so a stuck/failed track is diagnosable, not silent.
+    metadata_error: Mapped[str | None] = mapped_column(String(2048), nullable=True)
+    # When the last enrichment run finished (success or failure). ``None`` while
+    # still ``pending`` — lets the UI distinguish "queued/running" from "done".
+    enriched_at: Mapped[dt.datetime | None] = mapped_column(
+        DateTime(timezone=True),
+        nullable=True,
+    )
 
     added_by: Mapped[uuid.UUID | None] = mapped_column(
         ForeignKey("users.id", ondelete="SET NULL"),

app/infrastructure/db/repositories/like_repository.py

@@ -39,6 +39,8 @@ def _track_to_entity(row: TrackModel) -> Track:
         genre=row.genre,
         year=row.year,
         metadata_status=row.metadata_status,
+        metadata_error=row.metadata_error,
+        enriched_at=row.enriched_at,
         created_at=row.created_at,
         updated_at=row.updated_at,
     )

app/infrastructure/db/repositories/playlist_repository.py

@@ -38,6 +38,8 @@ def _track_to_entity(row: TrackModel) -> Track:
         genre=row.genre,
         year=row.year,
         metadata_status=row.metadata_status,
+        metadata_error=row.metadata_error,
+        enriched_at=row.enriched_at,
         created_at=row.created_at,
         updated_at=row.updated_at,
     )

app/infrastructure/db/repositories/track_repository.py

@@ -1,5 +1,6 @@
 """Track repository — adapter over ``AsyncSession``."""
 
+import datetime as dt
 import uuid
 
 from sqlalchemy import func, select
@@ -26,6 +27,8 @@ def _to_entity(row: TrackModel) -> Track:
         genre=row.genre,
         year=row.year,
         metadata_status=row.metadata_status,
+        metadata_error=row.metadata_error,
+        enriched_at=row.enriched_at,
         created_at=row.created_at,
         updated_at=row.updated_at,
     )
@@ -189,6 +192,7 @@ class SqlAlchemyTrackRepository:
         acoustid_fingerprint: str | None,
         musicbrainz_id: str | None,
         metadata_status: str,
+        metadata_error: str | None = None,
     ) -> Track:
         row = await self._session.get(TrackModel, track_id)
         if row is None:
@@ -197,6 +201,10 @@ class SqlAlchemyTrackRepository:
         row.title = title
         row.artist_id = artist_id
         row.metadata_status = metadata_status
+        # A finished run always stamps outcome: clear/set the reason and mark the
+        # completion time so the UI can tell "still pending" from "done/failed".
+        row.metadata_error = metadata_error
+        row.enriched_at = dt.datetime.now(dt.UTC)
         # Nullable extras: fill gaps only — never erase data a prior run found.
         if album_id is not None:
             row.album_id = album_id
@@ -217,3 +225,16 @@ class SqlAlchemyTrackRepository:
         await self._session.flush()
         await self._session.refresh(row)
         return _to_entity(row)
+
+    async def mark_enrichment_failed(self, track_id: uuid.UUID, *, error: str) -> None:
+        """Record that an enrichment run crashed (unexpected exception). Runs in
+        its own session so the failure is persisted even though the run's own
+        transaction rolled back. Never overwrites ``manual`` (a no-op then), and
+        a missing track is a clean no-op."""
+        row = await self._session.get(TrackModel, track_id)
+        if row is None or row.metadata_status == "manual":
+            return
+        row.metadata_status = "failed"
+        row.metadata_error = error
+        row.enriched_at = dt.datetime.now(dt.UTC)
+        await self._session.flush()