feat(api): GET /api/tracks/{id}/stream with Range support

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

internal/api/media.go

@@ -147,3 +147,42 @@ func (h *handlers) handleGetCover(w http.ResponseWriter, r *http.Request) {
 	w.Header().Set("Content-Type", imageContentType(path))
 	http.ServeContent(w, r, filepath.Base(path), info.ModTime(), f)
 }
+
+// handleGetStream implements GET /api/tracks/{id}/stream. Opens the file on
+// disk and delegates byte-serving to http.ServeContent, which handles Range,
+// If-Modified-Since, and ETag based on the file's mod time.
+func (h *handlers) handleGetStream(w http.ResponseWriter, r *http.Request) {
+	id, ok := parseUUID(chi.URLParam(r, "id"))
+	if !ok {
+		writeErr(w, http.StatusBadRequest, "bad_request", "invalid track id")
+		return
+	}
+	q := dbq.New(h.pool)
+	track, err := q.GetTrackByID(r.Context(), id)
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			writeErr(w, http.StatusNotFound, "not_found", "track not found")
+			return
+		}
+		h.logger.Error("api: get track for stream failed", "err", err)
+		writeErr(w, http.StatusInternalServerError, "server_error", "server error")
+		return
+	}
+	f, err := os.Open(track.FilePath)
+	if err != nil {
+		// File vanished (scanner indexed it, filesystem lost it). Treat as
+		// 404 so clients can fall back to the next item in a queue.
+		writeErr(w, http.StatusNotFound, "not_found", "track file not found")
+		return
+	}
+	defer func() { _ = f.Close() }()
+	info, err := f.Stat()
+	if err != nil {
+		h.logger.Error("api: stat track failed", "err", err)
+		writeErr(w, http.StatusInternalServerError, "server_error", "server error")
+		return
+	}
+	w.Header().Set("Content-Type", audioContentType(track.FileFormat))
+	w.Header().Set("Accept-Ranges", "bytes")
+	http.ServeContent(w, r, filepath.Base(track.FilePath), info.ModTime(), f)
+}