feat(server): GET /api/library/sync endpoint

Returns batched upserts + deletes since the supplied cursor. Empty cursor
returns full snapshot; subsequent calls pull deltas. Per-user entities
(likes, playlists) are scoped to the authed user. Composite-key entities
(likes, playlist_tracks) use stable string ids encoded by sync.EncodeLikeID
/ sync.EncodePlaylistTrackID.

Behavior:
  204 No Content - no changes since cursor
  200 OK         - JSON syncResponse {cursor, upserts, deletes}
  410 Gone       - cursor older than oldest log row; client must reset
  401 / 500      - standard envelope errors

Adds sqlc queries GetAlbumsByIDs, GetTracksByIDs, GetPlaylistsByIDs to
mirror the existing GetArtistsByIDs.

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

internal/db/dbq/albums.sql.go

@@ -168,6 +168,44 @@ func (q *Queries) GetAlbumCoverageRollup(ctx context.Context) (GetAlbumCoverageR
 	return i, err
 }
 
+const getAlbumsByIDs = `-- name: GetAlbumsByIDs :many
+SELECT id, title, sort_title, artist_id, release_date, mbid, cover_art_path, created_at, updated_at, cover_art_source, cover_art_sources_version FROM albums WHERE id = ANY($1::uuid[])
+`
+
+// Batched lookup used by /api/library/sync to hydrate upsert payloads
+// (#357). Mirror of GetArtistsByIDs.
+func (q *Queries) GetAlbumsByIDs(ctx context.Context, dollar_1 []pgtype.UUID) ([]Album, error) {
+	rows, err := q.db.Query(ctx, getAlbumsByIDs, dollar_1)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []Album
+	for rows.Next() {
+		var i Album
+		if err := rows.Scan(
+			&i.ID,
+			&i.Title,
+			&i.SortTitle,
+			&i.ArtistID,
+			&i.ReleaseDate,
+			&i.Mbid,
+			&i.CoverArtPath,
+			&i.CreatedAt,
+			&i.UpdatedAt,
+			&i.CoverArtSource,
+			&i.CoverArtSourcesVersion,
+		); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
 const listAlbumsAlphaByArtist = `-- name: ListAlbumsAlphaByArtist :many
 SELECT albums.id, albums.title, albums.sort_title, albums.artist_id, albums.release_date, albums.mbid, albums.cover_art_path, albums.created_at, albums.updated_at, albums.cover_art_source, albums.cover_art_sources_version, artists.sort_name AS artist_sort_name
 FROM albums

internal/db/dbq/playlists.sql.go

@@ -173,6 +173,46 @@ func (q *Queries) GetPlaylist(ctx context.Context, id pgtype.UUID) (GetPlaylistR
 	return i, err
 }
 
+const getPlaylistsByIDs = `-- name: GetPlaylistsByIDs :many
+SELECT id, user_id, name, description, is_public, cover_path, track_count, duration_sec, created_at, updated_at, kind, system_variant, seed_artist_id FROM playlists WHERE id = ANY($1::uuid[])
+`
+
+// Batched lookup used by /api/library/sync to hydrate upsert payloads
+// (#357). Mirror of GetArtistsByIDs.
+func (q *Queries) GetPlaylistsByIDs(ctx context.Context, dollar_1 []pgtype.UUID) ([]Playlist, error) {
+	rows, err := q.db.Query(ctx, getPlaylistsByIDs, dollar_1)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []Playlist
+	for rows.Next() {
+		var i Playlist
+		if err := rows.Scan(
+			&i.ID,
+			&i.UserID,
+			&i.Name,
+			&i.Description,
+			&i.IsPublic,
+			&i.CoverPath,
+			&i.TrackCount,
+			&i.DurationSec,
+			&i.CreatedAt,
+			&i.UpdatedAt,
+			&i.Kind,
+			&i.SystemVariant,
+			&i.SeedArtistID,
+		); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
 const listAllPlaylistTracksForCollage = `-- name: ListAllPlaylistTracksForCollage :many
 SELECT pt.position,
        albums.cover_art_path AS album_cover_path

internal/db/dbq/tracks.sql.go

@@ -143,6 +143,48 @@ func (q *Queries) GetTrackByPath(ctx context.Context, filePath string) (Track, e
 	return i, err
 }
 
+const getTracksByIDs = `-- name: GetTracksByIDs :many
+SELECT id, title, album_id, artist_id, track_number, disc_number, duration_ms, file_path, file_size, file_format, bitrate, mbid, genre, added_at, updated_at FROM tracks WHERE id = ANY($1::uuid[])
+`
+
+// Batched lookup used by /api/library/sync to hydrate upsert payloads
+// (#357). Mirror of GetArtistsByIDs.
+func (q *Queries) GetTracksByIDs(ctx context.Context, dollar_1 []pgtype.UUID) ([]Track, error) {
+	rows, err := q.db.Query(ctx, getTracksByIDs, dollar_1)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []Track
+	for rows.Next() {
+		var i Track
+		if err := rows.Scan(
+			&i.ID,
+			&i.Title,
+			&i.AlbumID,
+			&i.ArtistID,
+			&i.TrackNumber,
+			&i.DiscNumber,
+			&i.DurationMs,
+			&i.FilePath,
+			&i.FileSize,
+			&i.FileFormat,
+			&i.Bitrate,
+			&i.Mbid,
+			&i.Genre,
+			&i.AddedAt,
+			&i.UpdatedAt,
+		); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
 const listArtistTracksForUser = `-- name: ListArtistTracksForUser :many
 SELECT t.id, t.title, t.album_id, t.artist_id, t.track_number, t.disc_number, t.duration_ms, t.file_path, t.file_size, t.file_format, t.bitrate, t.mbid, t.genre, t.added_at, t.updated_at,
        albums.title AS album_title,

internal/db/queries/albums.sql

@@ -159,3 +159,8 @@ UPDATE albums
        updated_at                = now()
  WHERE id = $1;
 
+
+-- name: GetAlbumsByIDs :many
+-- Batched lookup used by /api/library/sync to hydrate upsert payloads
+-- (#357). Mirror of GetArtistsByIDs.
+SELECT * FROM albums WHERE id = ANY($1::uuid[]);

internal/db/queries/playlists.sql

@@ -108,3 +108,8 @@ LEFT JOIN albums   ON albums.id = t.album_id
 WHERE pt.playlist_id = $1
 ORDER BY pt.position
 LIMIT $2;
+
+-- name: GetPlaylistsByIDs :many
+-- Batched lookup used by /api/library/sync to hydrate upsert payloads
+-- (#357). Mirror of GetArtistsByIDs.
+SELECT * FROM playlists WHERE id = ANY($1::uuid[]);

internal/db/queries/tracks.sql

@@ -95,3 +95,8 @@ SELECT COUNT(*) FROM tracks WHERE artist_id = $1;
 -- checks the service does next.
 DELETE FROM tracks WHERE id = $1
 RETURNING id, album_id, artist_id, file_path, mbid;
+
+-- name: GetTracksByIDs :many
+-- Batched lookup used by /api/library/sync to hydrate upsert payloads
+-- (#357). Mirror of GetArtistsByIDs.
+SELECT * FROM tracks WHERE id = ANY($1::uuid[]);