feat(database): shape the library like files, and shrink the catalog

Plans 013 and 014, the album page that prompted them, and the smaller
fixes they turned up. Changelog, largest first.

## The local library is shaped like files, not like MusicBrainz

`audio_files` carries its own tags and points at `albums` and
`artists`; `file_genres` is the one real many-to-many. `recordings`,
`release_group_recordings`, `artist_credit`, `artist_credit_artist`,
`recording_genres`, `release_groups` and `release_to_rg` are gone from
the local side, and with them a six-way join in every read, a
`MIN(release_group_id)` subquery in eleven queries and a
first-credited-artist subquery in nine. Measured on a real 25,966-file
library, every many-to-many that model expressed was 1:1 in the data.

- Ownership is a file. `GetFilePathsByRecordingMBIDs`,
  `LibraryMBIDIndex.CheckMBIDs`, `collectLibraryEntities` and
  `pruneStaleLocalCrossReferences` all join `audio_files`, so the 812
  orphaned recordings, 216 release groups and 260 artists that library
  carried are now structurally impossible.
- One projection: every track query selects from the `track_metadata`
  view, one row type, one mapper. Nine hand-rolled copies had drifted
  far enough to report different years on different screens.
- `library_id = 0` means every library, so each list query exists once
  instead of scoped and unscoped with a branch at every call site.
- No migration chain. `sql/schemas/` is the one description of the
  shape; `sql/migrations/`, `applyMigrations` and `schema_migrations`
  are squashed away, along with the drift between them that had sqlc
  generating against a stale schema.
- `database.InsertTestTrack` is the one test seeder; twenty test files
  had been assembling the old FK chain each in its own order.

## The catalog stores its ids as bytes

`explore_index`'s three 36-char MBID columns and its entity-type text
are 16 raw bytes and a small integer. The table and its six indexes go
780 MB to 405 MB on a real 2,052,200-row catalog, which is why a fresh
install is ~0.6 GB rather than ~1.0 GB.

- `backend/explore/mbid.go` is the only place the encoding is known;
  everything above it speaks dashed strings.
- `CHECK(length(mbid) = 16)` makes a stringly write fail at the insert
  rather than silently returning no rows, since SQLite does not coerce
  between TEXT and BLOB.
- The importer asks the artifact what encoding it carries and converts
  on the way in, so the artifact already published keeps working and no
  format bump is needed.
- `indexRowColumns`/`scanIndexRow` replace four copies of a 22-column
  list, and `TestStoredEncodingRoundTrips` sweeps every read path.

## An album page that says how much of the album is yours

- One question, asked once: is there a file. `filePaths` is filled by a
  single batched lookup when the tracklist settles, and the badge, the
  Play count, the dimmed rows and every menu item read it — replacing
  four claims of decreasing confidence that could show a green tick on
  an album whose every action did nothing.
- Play, Play 7 of 12, or no play button at all.
- `total_tracks` on `explore_index` (~2 bytes over 400,677 release
  groups) and on `audio_files` from tags that have always carried it:
  a complete MBID-matched album now makes no catalog call at all, where
  it used to spend the most expensive request the app makes.
- A merged cluster shows the running order the most releases agree on,
  and the version list marks the release you own rather than standing a
  synthetic entry in for it.
- `AlbumReleasesFailed`: a slow fetch is no longer reported as a failed
  one by a 12-second timer.
- Rows not in the library are dimmed in place (with `aria-disabled`)
  instead of the owned ones wearing a green tick and a legend.

## Caches and cover art get ceilings

- Only the three tiers of a cover are stored; the full-resolution copy
  nothing rendered was 1,134 MB of a 1.4 GB covers directory.
- One artist portrait is downloaded and the rest are remembered as
  URLs — 4.1 GB of a 5.3 GB cache was candidates no code path reads.
- `browsedArtBudget` and `httpCacheBudget` bound what an age cannot:
  the same install held art for 5,770 artists in a 1,301-artist
  library.
- `OrphanedArtistImagesJob` joined a bare MBID onto a sharded
  directory, so it deleted the rows that were the only record of the
  files it left behind. `explore.ArtistImageDir` is that layout's one
  definition now.

## The autotag queue asks whether there is work

`tagging_items` was a row per album folder, not a queue, and no query
read the `tag_status` column that held the answer. The four queue
queries ask the files, which matters most where it is least visible:
`startPrefetch` was scoring every album in a tagged library against
MusicBrainz.

## Phantom playlist tracks resolve in place

An M3U8 imported before its files leaves phantom rows; they now match
by path and fall back to position, keep their place in the playlist
when resolved, and pair best-first so two phantoms cannot claim the
same file.

## Playing a track plays the list it is in

Double-click, and Play on a single row's menu, queue the list as
displayed with `startIndex` on that row — the album page and the track
list used to queue one track and discard the album around it. A
multi-row selection still plays exactly itself.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AfVYUVExXsx1nSWrXN8mAh

backend/database/lyrics_search.go

@@ -1,15 +1,26 @@
 package database
 
 import (
+	"database/sql"
+	"errors"
 	"fmt"
 	"strings"
 	"unicode"
 )
 
+// toNullString treats an empty string as NULL.
+func toNullString(v string) sql.NullString {
+	if v == "" {
+		return sql.NullString{}
+	}
+
+	return sql.NullString{String: v, Valid: true}
+}
+
 // LyricsHit is a single result from a lyric-fragment search: the
-// matched recording plus enough metadata to render and play it.
+// matched file plus enough metadata to render and play it.
 type LyricsHit struct {
-	RecordingID        int64
+	AudioFileID        int64
 	FilePath           string
 	LengthMilliseconds int64
 	Title              string
@@ -37,27 +48,22 @@ func (d *DB) SearchLyrics(query string, limit int) ([]LyricsHit, error) {
 		return nil, nil
 	}
 
-	// Map the matched recording (lyrics_index.rowid == recordings.id)
-	// to a representative playable file via the lowest audio_files id,
-	// then to the track_metadata VIEW for display fields.
+	// lyrics_index.rowid is the audio file's id, so the hit is already
+	// a playable file - it used to be a recording id, which then had to
+	// be mapped back to "some file of that recording" by a grouped
+	// subquery.
 	//
 	// SAFETY: FTS5 MATCH syntax unsupported by sqlc. Query is parameterized; no string interpolation.
-	rows, err := d.db.QueryContext(d.Ctx, `
+	rows, err := d.reader().QueryContext(d.Ctx, `
 		SELECT
-			r.id,
+			tm.id,
 			tm.file_path,
 			tm.length_milliseconds,
 			tm.title,
 			tm.artist_name,
 			tm.album
 		FROM lyrics_index li
-		JOIN recordings r ON r.id = li.rowid
-		JOIN (
-			SELECT recording_id, MIN(id) AS af_id
-			FROM audio_files
-			GROUP BY recording_id
-		) af ON af.recording_id = r.id
-		JOIN track_metadata tm ON tm.id = af.af_id
+		JOIN track_metadata tm ON tm.id = li.rowid
 		WHERE lyrics_index MATCH ?
 		ORDER BY rank
 		LIMIT ?
@@ -73,7 +79,7 @@ func (d *DB) SearchLyrics(query string, limit int) ([]LyricsHit, error) {
 	for rows.Next() {
 		var h LyricsHit
 		if err := rows.Scan(
-			&h.RecordingID,
+			&h.AudioFileID,
 			&h.FilePath,
 			&h.LengthMilliseconds,
 			&h.Title,
@@ -93,43 +99,64 @@ func (d *DB) SearchLyrics(query string, limit int) ([]LyricsHit, error) {
 	return results, nil
 }
 
-// GetRecordingLyrics returns the stored lyrics for a recording, or
-// an empty string if none are stored.
-func (d *DB) GetRecordingLyrics(recordingID int64) (string, error) {
+// GetLyrics returns the stored lyrics for a file, or "" if none.
+func (d *DB) GetLyrics(audioFileID int64) (string, error) {
 	var lyrics string
 
-	err := d.db.QueryRowContext(d.Ctx,
-		"SELECT COALESCE(lyrics, '') FROM recordings WHERE id = ?",
-		recordingID,
+	err := d.reader().QueryRowContext(d.Ctx,
+		"SELECT text FROM lyrics WHERE audio_file_id = ?", audioFileID,
 	).Scan(&lyrics)
+
+	if errors.Is(err, sql.ErrNoRows) {
+		return "", nil
+	}
+
 	if err != nil {
-		return "", fmt.Errorf("could not read recording lyrics: %w", err)
+		return "", fmt.Errorf("could not read lyrics: %w", err)
 	}
 
 	return lyrics, nil
 }
 
-// SetRecordingLyrics writes lyrics onto a recording and keeps the FTS
-// lyrics_index in sync (delete + reinsert the single row).  Used by
-// the LRCLIB backfill to persist fetched lyrics.  Passing an empty
-// string clears both the column and the index entry.
-func (d *DB) SetRecordingLyrics(recordingID int64, lyrics string) error {
-	if _, err := d.db.ExecContext(d.Ctx,
-		"UPDATE recordings SET lyrics = ? WHERE id = ?",
-		lyrics, recordingID,
-	); err != nil {
-		return fmt.Errorf("could not update recording lyrics: %w", err)
+// SetLyrics writes lyrics for a file and keeps the FTS index in sync.
+//
+// `source` says where they came from, which is the question the old
+// column could not answer: lyrics read from a USLT frame are rebuilt
+// free by any rescan, and lyrics fetched from LRCLIB are network
+// traffic nobody wants to repeat.  Passing an empty string clears both
+// the row and the index entry.
+func (d *DB) SetLyrics(audioFileID int64, lyrics, source, recordingMBID string) error {
+	if strings.TrimSpace(lyrics) == "" {
+		if _, err := d.db.ExecContext(d.Ctx,
+			"DELETE FROM lyrics WHERE audio_file_id = ?", audioFileID,
+		); err != nil {
+			return fmt.Errorf("could not delete lyrics: %w", err)
+		}
+
+		return d.upsertLyricsIndex(audioFileID, "")
 	}
 
-	return d.upsertLyricsIndex(recordingID, lyrics)
+	if _, err := d.db.ExecContext(d.Ctx, `
+		INSERT INTO lyrics (audio_file_id, text, source, recording_mbid)
+		VALUES (?, ?, ?, ?)
+		ON CONFLICT(audio_file_id) DO UPDATE SET
+			text = excluded.text,
+			source = excluded.source,
+			recording_mbid = COALESCE(excluded.recording_mbid, lyrics.recording_mbid),
+			fetched_at = CURRENT_TIMESTAMP
+	`, audioFileID, lyrics, source, toNullString(recordingMBID)); err != nil {
+		return fmt.Errorf("could not write lyrics: %w", err)
+	}
+
+	return d.upsertLyricsIndex(audioFileID, lyrics)
 }
 
-// upsertLyricsIndex refreshes a single recording's entry in the
-// contentless lyrics_index.  contentless_delete=1 makes the DELETE
-// valid; an empty lyrics string leaves the row deleted.
-func (d *DB) upsertLyricsIndex(recordingID int64, lyrics string) error {
+// upsertLyricsIndex refreshes a single file's entry in the contentless
+// lyrics_index.  contentless_delete=1 makes the DELETE valid; an empty
+// lyrics string leaves the row deleted.
+func (d *DB) upsertLyricsIndex(audioFileID int64, lyrics string) error {
 	if _, err := d.db.ExecContext(d.Ctx,
-		"DELETE FROM lyrics_index WHERE rowid = ?", recordingID,
+		"DELETE FROM lyrics_index WHERE rowid = ?", audioFileID,
 	); err != nil {
 		return fmt.Errorf("could not delete lyrics_index row: %w", err)
 	}
@@ -141,7 +168,7 @@ func (d *DB) upsertLyricsIndex(recordingID int64, lyrics string) error {
 	// SAFETY: FTS5 virtual table INSERT unsupported by sqlc. All values parameterized.
 	if _, err := d.db.ExecContext(d.Ctx,
 		"INSERT INTO lyrics_index(rowid, lyrics) VALUES (?, ?)",
-		recordingID, lyrics,
+		audioFileID, lyrics,
 	); err != nil {
 		return fmt.Errorf("could not insert lyrics_index row: %w", err)
 	}
@@ -149,22 +176,16 @@ func (d *DB) upsertLyricsIndex(recordingID int64, lyrics string) error {
 	return nil
 }
 
-// RebuildLyricsIndex repopulates lyrics_index from scratch using the
-// current recordings table.  Cheap for a personal library and safe to
-// run after every scan.
+// RebuildLyricsIndex repopulates lyrics_index from the lyrics table.
 func (d *DB) RebuildLyricsIndex() error {
-	if _, err := d.db.ExecContext(d.Ctx,
-		"DELETE FROM lyrics_index",
-	); err != nil {
+	if _, err := d.db.ExecContext(d.Ctx, "DELETE FROM lyrics_index"); err != nil {
 		return fmt.Errorf("could not clear lyrics_index: %w", err)
 	}
 
-	// SAFETY: FTS5 virtual table INSERT unsupported by sqlc. Values sourced from recordings; no user input.
+	// SAFETY: FTS5 virtual table INSERT. Values sourced from lyrics; no user input.
 	if _, err := d.db.ExecContext(d.Ctx, `
 		INSERT INTO lyrics_index(rowid, lyrics)
-		SELECT id, lyrics
-		FROM recordings
-		WHERE lyrics IS NOT NULL AND lyrics != ''
+		SELECT audio_file_id, text FROM lyrics WHERE text != ''
 	`); err != nil {
 		return fmt.Errorf("could not rebuild lyrics_index: %w", err)
 	}
@@ -172,39 +193,35 @@ func (d *DB) RebuildLyricsIndex() error {
 	return nil
 }
 
-// RecordingsMissingLyrics returns recordings that have no stored
-// lyrics but do carry the artist/title/duration needed to look them
-// up from an external provider.  Used by the LRCLIB backfill.  The
-// limit bounds each batch so the backfill can be run incrementally.
-func (d *DB) RecordingsMissingLyrics(limit int) ([]LyricsCandidate, error) {
+// LyricsCandidate identifies a file that needs its lyrics fetched and
+// carries the fields an external provider matches on.
+type LyricsCandidate struct {
+	AudioFileID        int64
+	Title              string
+	Artist             string
+	Album              string
+	RecordingMBID      string
+	LengthMilliseconds int64
+}
+
+// FilesMissingLyrics returns files with no stored lyrics that carry
+// the artist/title/duration needed to look them up.  Used by the
+// LRCLIB backfill; the limit bounds each batch.
+func (d *DB) FilesMissingLyrics(limit int) ([]LyricsCandidate, error) {
 	if limit <= 0 {
 		limit = 200
 	}
 
-	rows, err := d.db.QueryContext(d.Ctx, `
-		SELECT
-			r.id,
-			COALESCE(r.name, ''),
-			COALESCE(ac.text, ''),
-			COALESCE(rg.name, ''),
-			MIN(af.length_milliseconds)
-		FROM recordings r
-		JOIN audio_files af ON af.recording_id = r.id
-		LEFT JOIN artist_credit ac ON r.artist_credit_id = ac.id
-		LEFT JOIN (
-			SELECT recording_id, MIN(release_group_id) AS release_group_id
-			FROM release_group_recordings
-			GROUP BY recording_id
-		) rgr ON rgr.recording_id = r.id
-		LEFT JOIN release_groups rg ON rg.id = rgr.release_group_id
-		WHERE (r.lyrics IS NULL OR r.lyrics = '')
-		  AND r.name IS NOT NULL AND r.name != ''
-		  AND ac.text IS NOT NULL AND ac.text != ''
-		GROUP BY r.id
+	rows, err := d.reader().QueryContext(d.Ctx, `
+		SELECT tm.id, tm.title, tm.artist_name, tm.album,
+		       tm.recording_mbid, tm.length_milliseconds
+		FROM track_metadata tm
+		WHERE NOT EXISTS (SELECT 1 FROM lyrics l WHERE l.audio_file_id = tm.id)
+		  AND tm.title != '' AND tm.artist_name != ''
 		LIMIT ?
 	`, limit)
 	if err != nil {
-		return nil, fmt.Errorf("could not query recordings missing lyrics: %w", err)
+		return nil, fmt.Errorf("could not query files missing lyrics: %w", err)
 	}
 
 	defer func() { _ = rows.Close() }()
@@ -214,7 +231,8 @@ func (d *DB) RecordingsMissingLyrics(limit int) ([]LyricsCandidate, error) {
 	for rows.Next() {
 		var c LyricsCandidate
 		if err := rows.Scan(
-			&c.RecordingID, &c.Title, &c.Artist, &c.Album, &c.LengthMilliseconds,
+			&c.AudioFileID, &c.Title, &c.Artist, &c.Album,
+			&c.RecordingMBID, &c.LengthMilliseconds,
 		); err != nil {
 			return nil, fmt.Errorf("could not scan lyrics candidate: %w", err)
 		}
@@ -229,44 +247,23 @@ func (d *DB) RecordingsMissingLyrics(limit int) ([]LyricsCandidate, error) {
 	return out, nil
 }
 
-// LyricsCandidate identifies a recording that needs its lyrics fetched
-// and carries the fields an external provider matches on.
-type LyricsCandidate struct {
-	RecordingID        int64
-	Title              string
-	Artist             string
-	Album              string
-	LengthMilliseconds int64
-}
-
-// RecordingLyricLookup returns the provider-match fields (artist,
-// title, album, duration) for a single recording, so lyrics can be
-// fetched on demand.  Returns nil if the recording has no audio file
-// or no artist/title to match on.
-func (d *DB) RecordingLyricLookup(recordingID int64) (*LyricsCandidate, error) {
+// FileLyricLookup returns the provider-match fields for one file, so
+// lyrics can be fetched on demand.  Returns nil if the file has no
+// artist/title to match on.
+func (d *DB) FileLyricLookup(audioFileID int64) (*LyricsCandidate, error) {
 	var c LyricsCandidate
 
-	err := d.db.QueryRowContext(d.Ctx, `
-		SELECT
-			r.id,
-			COALESCE(r.name, ''),
-			COALESCE(ac.text, ''),
-			COALESCE(rg.name, ''),
-			COALESCE(MIN(af.length_milliseconds), 0)
-		FROM recordings r
-		JOIN audio_files af ON af.recording_id = r.id
-		LEFT JOIN artist_credit ac ON r.artist_credit_id = ac.id
-		LEFT JOIN (
-			SELECT recording_id, MIN(release_group_id) AS release_group_id
-			FROM release_group_recordings
-			GROUP BY recording_id
-		) rgr ON rgr.recording_id = r.id
-		LEFT JOIN release_groups rg ON rg.id = rgr.release_group_id
-		WHERE r.id = ?
-		GROUP BY r.id
-	`, recordingID).Scan(&c.RecordingID, &c.Title, &c.Artist, &c.Album, &c.LengthMilliseconds)
+	err := d.reader().QueryRowContext(d.Ctx, `
+		SELECT tm.id, tm.title, tm.artist_name, tm.album,
+		       tm.recording_mbid, tm.length_milliseconds
+		FROM track_metadata tm
+		WHERE tm.id = ?
+	`, audioFileID).Scan(
+		&c.AudioFileID, &c.Title, &c.Artist, &c.Album,
+		&c.RecordingMBID, &c.LengthMilliseconds,
+	)
 	if err != nil {
-		return nil, fmt.Errorf("could not look up recording for lyrics: %w", err)
+		return nil, fmt.Errorf("could not look up file for lyrics: %w", err)
 	}
 
 	if c.Title == "" || c.Artist == "" {