feat(server): scanner + DeleteTrackFile write library_changes

Wires sync.LogChange into the library mutation sites so /api/library/sync
reflects upserts and deletes.

Architectural pivot: LogChange's signature is now (ctx, dbq.DBTX, ...) so
it works with both *pgxpool.Pool and pgx.Tx. The scanner doesn't run
mutations in explicit transactions, so it pool-binds; delete.go matches.
Tx-bound callers (likes/playlists in subsequent commits) keep atomicity.

Also: sync.FormatUUID centralizes the pgtype.UUID → canonical string
conversion that both the scanner and the sync handler need; library_sync.go
now uses it instead of a local copy.

Best-effort logging on scanner failures (Warn, don't fail the scan): a
LogChange error after a successful upsert is rare and self-healing — the
next scan that touches the entity re-emits the change.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/library/delete.go

@@ -12,6 +12,7 @@ import (
 	"github.com/jackc/pgx/v5/pgxpool"
 
 	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
+	syncpkg "git.fabledsword.com/bvandeusen/minstrel/internal/sync"
 )
 
 // ErrTrackNotFound is returned when DeleteTrackFile is called with an id
@@ -48,5 +49,12 @@ func DeleteTrackFile(ctx context.Context, pool *pgxpool.Pool, trackID pgtype.UUI
 	if _, err := pool.Exec(ctx, "DELETE FROM tracks WHERE id = $1", trackID); err != nil {
 		return fmt.Errorf("delete row: %w", err)
 	}
+	// Log the change after the delete succeeds. Best-effort: a Warn-level
+	// failure here would leave the cache index orphaned on offline clients
+	// until the next scan touches the surrounding album.
+	if err := syncpkg.LogChange(ctx, pool, syncpkg.EntityTrack,
+		syncpkg.FormatUUID(trackID), syncpkg.OpDelete); err != nil {
+		return fmt.Errorf("log change: %w", err)
+	}
 	return nil
 }

internal/library/scanner.go

@@ -20,6 +20,7 @@ import (
 	"github.com/jackc/pgx/v5/pgxpool"
 
 	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
+	syncpkg "git.fabledsword.com/bvandeusen/minstrel/internal/sync"
 )
 
 // audioExtensions is the v1 set. Duration extraction is not wired, so all of
@@ -195,9 +196,16 @@ func (s *Scanner) scanFile(ctx context.Context, q *dbq.Queries, path string, sta
 		params.Genre = &g
 	}
 
-	if _, err := q.UpsertTrack(ctx, params); err != nil {
+	track, err := q.UpsertTrack(ctx, params)
+	if err != nil {
 		return fmt.Errorf("upsert track: %w", err)
 	}
+	if err := syncpkg.LogChange(ctx, s.pool, syncpkg.EntityTrack,
+		syncpkg.FormatUUID(track.ID), syncpkg.OpUpsert); err != nil {
+		// Best-effort: log but don't fail the scan. The next scan that
+		// touches this track will re-emit the change.
+		s.logger.Warn("library scan: LogChange track upsert failed", "track_id", track.ID, "err", err)
+	}
 
 	if knownTrack {
 		stats.Updated++
@@ -236,7 +244,15 @@ func (s *Scanner) resolveArtist(ctx context.Context, q *dbq.Queries, name, mbid
 		m := mbid
 		params.Mbid = &m
 	}
-	return q.UpsertArtist(ctx, params)
+	artist, err := q.UpsertArtist(ctx, params)
+	if err != nil {
+		return dbq.Artist{}, err
+	}
+	if err := syncpkg.LogChange(ctx, s.pool, syncpkg.EntityArtist,
+		syncpkg.FormatUUID(artist.ID), syncpkg.OpUpsert); err != nil {
+		s.logger.Warn("library scan: LogChange artist upsert failed", "artist_id", artist.ID, "err", err)
+	}
+	return artist, nil
 }
 
 func (s *Scanner) resolveAlbum(ctx context.Context, q *dbq.Queries, artistID pgtype.UUID, title string, year int, mbid string) (dbq.Album, error) {
@@ -285,7 +301,15 @@ func (s *Scanner) resolveAlbum(ctx context.Context, q *dbq.Queries, artistID pgt
 		m := mbid
 		params.Mbid = &m
 	}
-	return q.UpsertAlbum(ctx, params)
+	album, err := q.UpsertAlbum(ctx, params)
+	if err != nil {
+		return dbq.Album{}, err
+	}
+	if err := syncpkg.LogChange(ctx, s.pool, syncpkg.EntityAlbum,
+		syncpkg.FormatUUID(album.ID), syncpkg.OpUpsert); err != nil {
+		s.logger.Warn("library scan: LogChange album upsert failed", "album_id", album.ID, "err", err)
+	}
+	return album, nil
 }
 
 // releaseDateFromYear converts a tag-supplied year into a Postgres date,