feat(api): GET /api/albums/{id} with nested tracks

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/api/library.go

@@ -45,9 +45,50 @@ func (h *handlers) handleGetTrack(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, trackRefFrom(track, album.Title, artist.Name))
 }
 
-// handleGetAlbum is implemented in Task 7.
+// handleGetAlbum implements GET /api/albums/{id}. Returns the album plus its
+// tracks (ordered by disc/track number via the underlying query) with
+// duration summed from the track list — keeps one source of truth.
 func (h *handlers) handleGetAlbum(w http.ResponseWriter, r *http.Request) {
-	writeErr(w, http.StatusNotImplemented, "not_implemented", "stub")
+	id, ok := parseUUID(chi.URLParam(r, "id"))
+	if !ok {
+		writeErr(w, http.StatusBadRequest, "bad_request", "invalid album id")
+		return
+	}
+	q := dbq.New(h.pool)
+	album, err := q.GetAlbumByID(r.Context(), id)
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			writeErr(w, http.StatusNotFound, "not_found", "album not found")
+			return
+		}
+		h.logger.Error("api: get album failed", "err", err)
+		writeErr(w, http.StatusInternalServerError, "server_error", "lookup failed")
+		return
+	}
+	artist, err := q.GetArtistByID(r.Context(), album.ArtistID)
+	if err != nil {
+		h.logger.Error("api: get album artist failed", "err", err)
+		writeErr(w, http.StatusInternalServerError, "server_error", "lookup failed")
+		return
+	}
+	tracks, err := q.ListTracksByAlbum(r.Context(), id)
+	if err != nil {
+		h.logger.Error("api: list tracks failed", "err", err)
+		writeErr(w, http.StatusInternalServerError, "server_error", "lookup failed")
+		return
+	}
+	refs := make([]TrackRef, 0, len(tracks))
+	durSec := 0
+	for _, t := range tracks {
+		ref := trackRefFrom(t, album.Title, artist.Name)
+		refs = append(refs, ref)
+		durSec += ref.DurationSec
+	}
+	detail := AlbumDetail{
+		AlbumRef: albumRefFrom(album, artist.Name, len(tracks), durSec),
+		Tracks:   refs,
+	}
+	writeJSON(w, http.StatusOK, detail)
 }
 
 // handleGetArtist is implemented in Task 8.