feat(metadata): implement single-track metadata editor API (§A7/§1H)

Adds inline AcoustID match-finding (multiple ranked candidates via
lookup_all) and PUT /tracks/{id}/metadata for manual edits, resolving
artist/album and setting metadata_status=manual. Extends TrackOut with
genre/year/track_number.

app/api/deps.py

@@ -15,6 +15,7 @@ from fastapi.security import HTTPAuthorizationCredentials, HTTPBearer
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.application.auth_service import AuthService
+from app.application.metadata_service import MetadataEnrichmentService
 from app.application.streaming_service import StreamingService
 from app.application.subsonic_auth_service import SubsonicAuthService
 from app.application.upload_service import UploadService
@@ -35,6 +36,9 @@ from app.infrastructure.db.repositories import (
     SqlAlchemyTrackRepository,
     SqlAlchemyUserRepository,
 )
+from app.infrastructure.metadata.acoustid import AcoustIdHttpClient
+from app.infrastructure.metadata.fingerprint import FpcalcFingerprinter
+from app.infrastructure.metadata.tags import MutagenTagReader
 from app.infrastructure.sources.registry import SourceRegistry, build_source_registry
 from app.infrastructure.storage.provider import get_file_storage
 from app.workers.queue import enqueue_enrich
@@ -132,8 +136,34 @@ def get_streaming_service(session: SessionDep, storage: FileStorageDep) -> Strea
     )
 
 
+def get_metadata_service(
+    session: SessionDep, storage: FileStorageDep
+) -> MetadataEnrichmentService:
+    """Wires the §6.2 fingerprint/AcoustID adapters for read-only, inline use
+    (the metadata editor's "find matches" — §A7). The full pipeline (incl.
+    cover art) stays in the worker (`tasks/enrich_task.py`)."""
+    settings = get_settings()
+    api_key = settings.acoustid_api_key.get_secret_value() if settings.acoustid_api_key else None
+    acoustid = AcoustIdHttpClient(
+        api_key=api_key,
+        user_agent=settings.musicbrainz_user_agent,
+        api_url=settings.acoustid_api_url,
+    )
+    return MetadataEnrichmentService(
+        tracks=SqlAlchemyTrackRepository(session),
+        artists=SqlAlchemyArtistRepository(session),
+        albums=SqlAlchemyAlbumRepository(session),
+        storage=storage,
+        tag_reader=MutagenTagReader(),
+        fingerprinter=FpcalcFingerprinter(settings.fpcalc_path),
+        acoustid=acoustid,
+        acoustid_trust_score=settings.acoustid_trust_score,
+    )
+
+
 UploadServiceDep = Annotated[UploadService, Depends(get_upload_service)]
 StreamingServiceDep = Annotated[StreamingService, Depends(get_streaming_service)]
+MetadataServiceDep = Annotated[MetadataEnrichmentService, Depends(get_metadata_service)]
 
 
 # -- library repository deps ---------------------------------------------------

app/api/schemas/track.py

@@ -16,6 +16,9 @@ class TrackOut(BaseModel):
     duration_seconds: int | None
     file_format: str
     file_size: int
+    genre: str | None
+    year: int | None
+    track_number: int | None
     metadata_status: str
     metadata_error: str | None
     enriched_at: dt.datetime | None
@@ -28,3 +31,33 @@ class TrackUpdate(BaseModel):
     title: str | None = None
     genre: str | None = None
     year: int | None = None
+
+
+class MetadataMatch(BaseModel):
+    """One AcoustID candidate for the metadata editor's match picker (§A7)."""
+
+    acoustid: str
+    score: float
+    recording_mbid: str | None
+    release_group_mbid: str | None
+    title: str | None
+    artist: str | None
+    album: str | None
+    year: int | None
+
+
+class MetadataMatchesOut(BaseModel):
+    items: list[MetadataMatch]
+
+
+class MetadataApply(BaseModel):
+    """Manual edits / accepted match applied via ``PUT /tracks/{id}/metadata``.
+
+    Sets ``metadata_status = manual`` (never overwritten by auto-enrichment)."""
+
+    title: str | None = None
+    artist_name: str | None = None
+    album_title: str | None = None
+    year: int | None = None
+    genre: str | None = None
+    track_number: int | None = None

app/api/v1/tracks.py

@@ -12,11 +12,18 @@ from app.api.deps import (
     ArtistRepoDep,
     CurrentUser,
     FileStorageDep,
+    MetadataServiceDep,
     StreamUser,
     TrackRepoDep,
 )
 from app.api.schemas.pagination import PagedResponse
-from app.api.schemas.track import TrackOut, TrackUpdate
+from app.api.schemas.track import (
+    MetadataApply,
+    MetadataMatch,
+    MetadataMatchesOut,
+    TrackOut,
+    TrackUpdate,
+)
 from app.domain.entities.album import Album
 from app.domain.entities.track import Artist, Track
 from app.domain.errors import NotFoundError
@@ -41,6 +48,9 @@ async def _build_track_out(
             duration_seconds=t.duration_seconds,
             file_format=t.file_format,
             file_size=t.file_size,
+            genre=t.genre,
+            year=t.year,
+            track_number=t.track_number,
             metadata_status=t.metadata_status,
             metadata_error=t.metadata_error,
             enriched_at=t.enriched_at,
@@ -187,8 +197,83 @@ async def enrich_metadata(
 
 
 @router.get("/{track_id}/metadata/matches")
-async def get_metadata_matches(track_id: uuid.UUID, _: CurrentUser) -> Any: ...
+async def get_metadata_matches(
+    track_id: uuid.UUID,
+    track_repo: TrackRepoDep,
+    metadata_service: MetadataServiceDep,
+    _: CurrentUser,
+) -> MetadataMatchesOut:
+    """AcoustID candidates for the metadata editor's match picker (§A7).
+
+    Runs the fingerprint lookup inline (single track, user-triggered) and
+    never mutates the track. Degrades to an empty list if fpcalc/AcoustID are
+    unavailable or no match is found.
+    """
+    track = await track_repo.get_by_id(track_id)
+    if track is None:
+        raise NotFoundError(f"Track {track_id} not found.")
+    matches = await metadata_service.find_matches(track_id)
+    return MetadataMatchesOut(
+        items=[
+            MetadataMatch(
+                acoustid=m.acoustid,
+                score=m.score,
+                recording_mbid=m.recording_mbid,
+                release_group_mbid=m.release_group_mbid,
+                title=m.title,
+                artist=m.artist,
+                album=m.album,
+                year=m.year,
+            )
+            for m in matches
+        ]
+    )
 
 
 @router.put("/{track_id}/metadata")
-async def set_metadata(track_id: uuid.UUID, _: CurrentUser) -> Any: ...
+async def set_metadata(
+    track_id: uuid.UUID,
+    body: MetadataApply,
+    track_repo: TrackRepoDep,
+    artist_repo: ArtistRepoDep,
+    album_repo: AlbumRepoDep,
+    _: CurrentUser,
+) -> TrackOut:
+    """Apply manual edits or an accepted AcoustID match (§A7). Sets
+    ``metadata_status = manual`` — never overwritten by auto-enrichment."""
+    track = await track_repo.get_by_id(track_id)
+    if track is None:
+        raise NotFoundError(f"Track {track_id} not found.")
+
+    artist_id: uuid.UUID | None = None
+    if body.artist_name:
+        artist = await artist_repo.get_or_create(body.artist_name)
+        artist_id = artist.id
+
+    album_id: uuid.UUID | None = None
+    if body.album_title:
+        album = await album_repo.get_or_create(
+            title=body.album_title,
+            artist_id=artist_id or track.artist_id,
+            year=body.year,
+            musicbrainz_id=None,
+        )
+        album_id = album.id
+
+    track = await track_repo.update(
+        track_id,
+        title=body.title,
+        genre=body.genre,
+        year=body.year,
+        artist_id=artist_id,
+        album_id=album_id,
+        track_number=body.track_number,
+    )
+
+    artist_ids = [track.artist_id]
+    album_ids = [track.album_id] if track.album_id else []
+    artists = {a.id: a for a in await artist_repo.get_many(artist_ids)}
+    albums = {a.id: a for a in await album_repo.get_many(album_ids)}
+
+    items = await _build_track_out([track], artists, albums)
+    return items[0]

app/application/metadata_service.py

@@ -162,6 +162,29 @@ class MetadataEnrichmentService:
             return "No metadata match: AcoustID lookup is unavailable (no API key)."
         return "No metadata match found in tags or AcoustID."
 
+    async def find_matches(self, track_id: uuid.UUID) -> list[RecordingMatch]:
+        """AcoustID candidates for the metadata editor's match picker (§A7).
+
+        Read-only — unlike :meth:`enrich`, never touches the track. Runs
+        inline (single track, user-triggered) rather than via the worker.
+        Degrades to ``[]`` whenever fingerprinting/AcoustID is unavailable or
+        the file can't be read, same as the enrichment pipeline.
+        """
+        track = await self._tracks.get_by_id(track_id)
+        if track is None:
+            return []
+        if not self._acoustid.is_available() or not self._fingerprinter.is_available():
+            return []
+        try:
+            async with self._storage.as_local_path(track.storage_uri) as path:
+                fingerprint = await self._fingerprinter.calculate(path)
+            if fingerprint is None:
+                return []
+            return await self._acoustid.lookup_all(fingerprint)
+        except Exception:
+            log.warning("find_matches_failed", track_id=str(track_id))
+            return []
+
     async def _read_local(self, storage_uri: str) -> AudioTags | None:
         try:
             async with self._storage.as_local_path(storage_uri) as path:

app/domain/entities/track.py

@@ -27,6 +27,7 @@ class Track:
     duration_seconds: int | None
     genre: str | None
     year: int | None
+    track_number: int | None
     metadata_status: str
     metadata_error: str | None
     enriched_at: dt.datetime | None

app/domain/ports.py

@@ -302,10 +302,13 @@ class AudioFingerprinter(Protocol):
 class AcoustIdClient(Protocol):
     """AcoustID lookup. ``is_available`` is False without an API key (the whole
     fingerprint path is then skipped). ``lookup`` returns the best match or
-    ``None`` (no result / service down), never raising."""
+    ``None`` (no result / service down), never raising. ``lookup_all`` returns
+    the same candidates ranked by confidence (``[]`` on no result / unavailable
+    / error), for the metadata editor's match picker."""
 
     def is_available(self) -> bool: ...
     async def lookup(self, fingerprint: Fingerprint) -> RecordingMatch | None: ...
+    async def lookup_all(self, fingerprint: Fingerprint) -> list[RecordingMatch]: ...
 
 
 class CoverArtExtractor(Protocol):

app/infrastructure/db/repositories/like_repository.py

@@ -38,6 +38,7 @@ def _track_to_entity(row: TrackModel) -> Track:
         duration_seconds=row.duration_seconds,
         genre=row.genre,
         year=row.year,
+        track_number=row.track_number,
         metadata_status=row.metadata_status,
         metadata_error=row.metadata_error,
         enriched_at=row.enriched_at,

app/infrastructure/db/repositories/playlist_repository.py

@@ -37,6 +37,7 @@ def _track_to_entity(row: TrackModel) -> Track:
         duration_seconds=row.duration_seconds,
         genre=row.genre,
         year=row.year,
+        track_number=row.track_number,
         metadata_status=row.metadata_status,
         metadata_error=row.metadata_error,
         enriched_at=row.enriched_at,

app/infrastructure/db/repositories/track_repository.py

@@ -26,6 +26,7 @@ def _to_entity(row: TrackModel) -> Track:
         duration_seconds=row.duration_seconds,
         genre=row.genre,
         year=row.year,
+        track_number=row.track_number,
         metadata_status=row.metadata_status,
         metadata_error=row.metadata_error,
         enriched_at=row.enriched_at,
@@ -162,6 +163,9 @@ class SqlAlchemyTrackRepository:
         title: str | None,
         genre: str | None,
         year: int | None,
+        artist_id: uuid.UUID | None = None,
+        album_id: uuid.UUID | None = None,
+        track_number: int | None = None,
     ) -> Track:
         row = await self._session.get(TrackModel, track_id)
         if row is None:
@@ -172,6 +176,12 @@ class SqlAlchemyTrackRepository:
             row.genre = genre
         if year is not None:
             row.year = year
+        if artist_id is not None:
+            row.artist_id = artist_id
+        if album_id is not None:
+            row.album_id = album_id
+        if track_number is not None:
+            row.track_number = track_number
         row.metadata_status = "manual"
         await self._session.flush()
         await self._session.refresh(row)

app/infrastructure/metadata/acoustid.py

@@ -46,6 +46,18 @@ class AcoustIdHttpClient:
         return bool(self._api_key)
 
     async def lookup(self, fingerprint: Fingerprint) -> RecordingMatch | None:
+        payload = await self._lookup_raw(fingerprint)
+        if payload is None:
+            return None
+        return _parse_best_match(payload)
+
+    async def lookup_all(self, fingerprint: Fingerprint) -> list[RecordingMatch]:
+        payload = await self._lookup_raw(fingerprint)
+        if payload is None:
+            return []
+        return _parse_matches(payload)
+
+    async def _lookup_raw(self, fingerprint: Fingerprint) -> object | None:
         if not self._api_key:
             return None
         try:
@@ -65,13 +77,11 @@ class AcoustIdHttpClient:
                     },
                 )
             resp.raise_for_status()
-            payload = resp.json()
+            return resp.json()  # type: ignore[no-any-return]
         except httpx.HTTPError, ValueError:
             log.warning("acoustid_lookup_failed")
             return None
 
-        return _parse_best_match(payload)
-
     @classmethod
     async def _throttle(cls) -> None:
         async with cls._throttle_lock:
@@ -82,22 +92,39 @@ class AcoustIdHttpClient:
             cls._last_call_monotonic = time.monotonic()
 
 
+_MAX_MATCHES = 5
+
+
 def _parse_best_match(payload: object) -> RecordingMatch | None:
+    matches = _parse_matches(payload)
+    return matches[0] if matches else None
+
+
+def _parse_matches(payload: object) -> list[RecordingMatch]:
     if not isinstance(payload, dict) or payload.get("status") != "ok":
-        return None
+        return []
     results = payload.get("results")
     if not isinstance(results, list) or not results:
-        return None
+        return []
 
-    # Results are returned best-score-first; take the top scoring one.
-    best = max(results, key=lambda r: r.get("score", 0.0) if isinstance(r, dict) else 0.0)
-    if not isinstance(best, dict):
-        return None
+    # Results are returned best-score-first, but sort defensively and cap the
+    # number of candidates surfaced to the editor.
+    candidates = [r for r in results if isinstance(r, dict)]
+    candidates.sort(key=lambda r: r.get("score", 0.0), reverse=True)
 
-    acoustid = best.get("id")
+    matches: list[RecordingMatch] = []
+    for result in candidates[:_MAX_MATCHES]:
+        match = _parse_one(result)
+        if match is not None:
+            matches.append(match)
+    return matches
+
+
+def _parse_one(result: dict[str, object]) -> RecordingMatch | None:
+    acoustid = result.get("id")
     if not isinstance(acoustid, str):
         return None
-    score = float(best.get("score", 0.0))
+    score = float(result.get("score", 0.0))  # type: ignore[arg-type]
 
     recording_mbid: str | None = None
     release_group_mbid: str | None = None
@@ -105,7 +132,7 @@ def _parse_best_match(payload: object) -> RecordingMatch | None:
     artist: str | None = None
     album: str | None = None
 
-    recordings = best.get("recordings")
+    recordings = result.get("recordings")
     if isinstance(recordings, list) and recordings and isinstance(recordings[0], dict):
         rec = recordings[0]
         recording_mbid = rec.get("id") if isinstance(rec.get("id"), str) else None