fix(queue): stop claiming a queue came from somewhere it no longer does

`q.source` was written by SetQueue and cleared in exactly one place,
Clear, so no append path touched it: adding a track to a queue built
from an album left the page still offering "Playing from <that album>",
and since the source is persisted alongside the queue state the wrong
label outlived the session that earned it.

Every add and insert path drops it now. Removing and reordering
deliberately do not — a queue with a track taken out of it is still
that album, and the link still goes somewhere true. Only the arrival of
a track from elsewhere makes the claim false.

The delta event carries the source for the same reason it carries the
current index: an append emits nothing else, so the frontend would keep
the label it was last given until something forced a full state.

Closes #14

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

backend/queue/emit.go

@@ -81,6 +81,7 @@ func (q *Queue) emitTracksModified(
 			Index:        index,
 			Positions:    positions,
 			CurrentIndex: q.currentIndex,
+			Source:       q.source,
 		},
 	)
 }

backend/queue/emit_test.go

@@ -219,6 +219,56 @@ func TestEmit_AddTrackSendsDeltaNotSnapshot(t *testing.T) {
 	}
 }
 
+// The append clears the source, and the delta is the only event those
+// paths emit — so if it does not carry the source, the frontend keeps
+// the label it was last given and goes on offering a link back to an
+// album the queue no longer holds until something forces a full state.
+func TestEmit_AppendDeltaCarriesClearedSource(t *testing.T) {
+	t.Parallel()
+
+	q, db, rec := setupRecordedQueue(t)
+	paths := seedAudioFiles(t, db, 4)
+
+	q.SetQueue(
+		paths[:3], 0, false,
+		Source{Type: "album", ID: 1, Label: "Abbey Road"},
+	)
+
+	if _, ok := rec.Wait(events.QueueChanged, waitFor); !ok {
+		t.Fatalf("no QueueChanged after SetQueue; got %v", rec.Names())
+	}
+
+	rec.Reset()
+	q.AddTrack(paths[3])
+
+	if got := modifiedOf(t, rec).Source; got != (Source{}) {
+		t.Errorf("delta source = %+v, want zero value", got)
+	}
+}
+
+// And a delta that did not clear it still reports the source it has,
+// or the frontend would drop a perfectly good label on every removal.
+func TestEmit_NonAppendDeltaCarriesSource(t *testing.T) {
+	t.Parallel()
+
+	q, db, rec := setupRecordedQueue(t)
+	paths := seedAudioFiles(t, db, 4)
+
+	album := Source{Type: "album", ID: 1, Label: "Abbey Road"}
+	q.SetQueue(paths, 0, false, album)
+
+	if _, ok := rec.Wait(events.QueueChanged, waitFor); !ok {
+		t.Fatalf("no QueueChanged after SetQueue; got %v", rec.Names())
+	}
+
+	rec.Reset()
+	q.RemoveTrack(3)
+
+	if got := modifiedOf(t, rec).Source; got != album {
+		t.Errorf("delta source = %+v, want %+v", got, album)
+	}
+}
+
 func TestEmit_RemoveTracksReportsPositions(t *testing.T) {
 	t.Parallel()
 

backend/queue/queue.go

@@ -156,12 +156,21 @@ type PlaybackFailure struct {
 }
 
 // TracksModified is the payload for the QueueTracksModified event.
+//
+// Source is carried because an append is exactly what can *invalidate*
+// it: a queue built from one album stops being that album the moment a
+// track from somewhere else is added to it. The delta is the only event
+// those paths emit, so without this the frontend would keep the label
+// it was last given and go on saying "Playing from" an album that is no
+// longer what is queued — an event carrying what its consumer needs, so
+// nothing has to invalidate anything.
 type TracksModified struct {
 	Action       string  `json:"action"`
 	Tracks       []Track `json:"tracks,omitempty"`
 	Index        int     `json:"index"`
 	Positions    []int   `json:"positions,omitempty"`
 	CurrentIndex int     `json:"currentIndex"`
+	Source       Source  `json:"source"`
 }
 
 // Queue manages an ordered list of tracks for playback.
@@ -455,6 +464,8 @@ func (q *Queue) AddTrack(filePath string) {
 		q.generateShuffleOrder()
 	}
 
+	q.dropSource()
+
 	q.persistAddTrack(track)
 	q.persistState()
 	q.emitTracksModified(
@@ -505,6 +516,8 @@ func (q *Queue) AddTracks(filePaths []string) {
 		q.generateShuffleOrder()
 	}
 
+	q.dropSource()
+
 	q.persistAddTracks(newTracks)
 	q.persistState()
 	q.emitTracksModified(
@@ -563,6 +576,8 @@ func (q *Queue) InsertNextTracks(filePaths []string) {
 		q.generateShuffleOrder()
 	}
 
+	q.dropSource()
+
 	q.persistInsertTracks(newTracks, insertPos)
 	q.persistState()
 	q.emitTracksModified(
@@ -613,6 +628,8 @@ func (q *Queue) InsertNext(filePath string) {
 		q.generateShuffleOrder()
 	}
 
+	q.dropSource()
+
 	q.persistInsertTracks([]Track{track}, insertPos)
 	q.persistState()
 	q.emitTracksModified(
@@ -680,6 +697,8 @@ func (q *Queue) InsertTracksAt(filePaths []string, index int) {
 		q.generateShuffleOrder()
 	}
 
+	q.dropSource()
+
 	q.persistInsertTracks(newTracks, index)
 	q.persistState()
 	q.emitTracksModified(
@@ -1537,6 +1556,31 @@ func (q *Queue) reindexPositions() {
 	}
 }
 
+// dropSource forgets which collection the queue was built from.
+//
+// A Source is a claim that everything queued came from one album,
+// playlist, genre or artist, and the frontend renders it as a
+// "Playing from X" link back to that page. Adding or inserting a track
+// makes the claim false — the queue is now that album *plus* something
+// else — so every path that does so calls this.
+//
+// It was set by SetQueue and cleared in exactly one place, Clear, so a
+// label survived every append. It is persisted too (source_type /
+// source_id / source_label on the queue state row), which is what made
+// a wrong label outlive the session that earned it: an album queued on
+// Monday, added to on Tuesday, still offered a link back to that album
+// on Friday.
+//
+// Removing, reordering and shuffling deliberately do not call this. A
+// queue with a track taken out of it, or played in another order, is
+// still that album — the link still goes somewhere true. Only the
+// arrival of a track from elsewhere makes it a lie.
+//
+// The caller must hold q.mu.
+func (q *Queue) dropSource() {
+	q.source = Source{}
+}
+
 // commitMutation persists the current queue state after a mutation.
 // When reindex is true, track positions are renumbered first.
 // The caller must hold q.mu.

backend/queue/queue_test.go

@@ -126,6 +126,117 @@ func TestClear_ResetsSource(t *testing.T) {
 	}
 }
 
+// A queue built from one album stops being that album the moment a
+// track from somewhere else joins it, so every path that adds one
+// drops the source. Before this, SetQueue was the only writer and
+// Clear the only clearer, so "Playing from Abbey Road" outlived every
+// append — and, being persisted, every restart too.
+func TestAppendPathsDropSource(t *testing.T) {
+	t.Parallel()
+
+	album := Source{Type: "album", ID: 1, Label: "Abbey Road"}
+
+	tests := []struct {
+		name   string
+		append func(q *Queue, paths []string)
+	}{
+		{
+			name: "AddTrack",
+			append: func(q *Queue, paths []string) {
+				q.AddTrack(paths[5])
+			},
+		},
+		{
+			name: "AddTracks",
+			append: func(q *Queue, paths []string) {
+				q.AddTracks(paths[5:7])
+			},
+		},
+		{
+			name: "InsertNext",
+			append: func(q *Queue, paths []string) {
+				q.InsertNext(paths[5])
+			},
+		},
+		{
+			name: "InsertNextTracks",
+			append: func(q *Queue, paths []string) {
+				q.InsertNextTracks(paths[5:7])
+			},
+		},
+		{
+			name: "InsertTracksAt",
+			append: func(q *Queue, paths []string) {
+				q.InsertTracksAt(paths[5:7], 1)
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			q, db := setupTestQueue(t)
+			paths := seedAudioFiles(t, db, 8)
+
+			q.SetQueue(paths[:5], 0, false, album)
+
+			if got := q.GetState().Source; got != album {
+				t.Fatalf("source before append: got %+v, want %+v", got, album)
+			}
+
+			tt.append(q, paths)
+
+			if got := q.GetState().Source; got != (Source{}) {
+				t.Errorf(
+					"source after %s: got %+v, want zero value",
+					tt.name, got,
+				)
+			}
+		})
+	}
+}
+
+// Removing and reordering deliberately do not drop it: a queue with a
+// track taken out of it is still that album, and the link still goes
+// somewhere true.
+func TestRemoveAndMoveKeepSource(t *testing.T) {
+	t.Parallel()
+
+	album := Source{Type: "album", ID: 1, Label: "Abbey Road"}
+
+	t.Run("RemoveTrack", func(t *testing.T) {
+		t.Parallel()
+
+		q, db := setupTestQueue(t)
+		paths := seedAudioFiles(t, db, 5)
+
+		q.SetQueue(paths, 0, false, album)
+		q.RemoveTrack(3)
+
+		if got := q.GetState().Source; got != album {
+			t.Errorf("source after RemoveTrack: got %+v, want %+v", got, album)
+		}
+	})
+
+	t.Run("MoveQueueTracks", func(t *testing.T) {
+		t.Parallel()
+
+		q, db := setupTestQueue(t)
+		paths := seedAudioFiles(t, db, 5)
+
+		q.SetQueue(paths, 0, false, album)
+		q.MoveQueueTracks([]int{0}, 3)
+
+		if got := q.GetState().Source; got != album {
+			t.Errorf(
+				"source after MoveQueueTracks: got %+v, want %+v",
+				got, album,
+			)
+		}
+	})
+}
+
 func TestSetQueue_WithStartIndex(t *testing.T) {
 	t.Parallel()
 

frontend/src/store/queue-store.ts

@@ -57,6 +57,12 @@ interface TracksModified {
   index: number;
   positions?: number[];
   currentIndex: number;
+  /** The queue's source *after* the mutation. An append clears it
+   *  backend-side — a queue built from one album is not that album
+   *  once a track from elsewhere joins it — and this delta is the
+   *  only event those paths emit, so the label would otherwise keep
+   *  pointing at a collection the queue no longer holds. */
+  source?: QueueSource;
 }
 
 type Subscriber = () => void;
@@ -198,6 +204,7 @@ class QueueStore {
     }
 
     this.state.currentIndex = delta.currentIndex;
+    this.state.source = delta.source ?? EMPTY_QUEUE_SOURCE;
   }
 
   // ===================================================================

frontend/test/stores/queue-store.test.ts

@@ -198,6 +198,61 @@ describe('queue store: move', () => {
   });
 });
 
+/**
+ * "Playing from X" is a claim that everything queued came from X, and
+ * appending a track from anywhere else makes it false. The backend
+ * clears the source on every add/insert path — but the delta is the
+ * only event those paths emit, so the label corrects itself here or
+ * not at all.
+ */
+describe('queue store: the source travels on the delta', () => {
+  function syncWithAlbum(): void {
+    emit(Events.QueueChanged, {
+      tracks: [track(1), track(2)],
+      currentIndex: 0,
+      shuffleMode: false,
+      repeatMode: 'off',
+      source: { type: 'album', id: 7, label: 'Abbey Road' },
+    });
+  }
+
+  beforeEach(() => {
+    syncWithAlbum();
+  });
+
+  it('drops the label when an append clears it backend-side', () => {
+    emit(Events.QueueTracksModified, {
+      action: 'add',
+      tracks: [track(3)],
+      index: 2,
+      currentIndex: 0,
+      source: { type: '', id: 0, label: '' },
+    });
+
+    expect(queueStore.getState().source).toEqual({
+      type: '',
+      id: 0,
+      label: '',
+    });
+  });
+
+  it('keeps a label the backend still reports, as on a removal', () => {
+    emit(Events.QueueTracksModified, {
+      action: 'remove',
+      positions: [1],
+      index: 0,
+      currentIndex: 0,
+      source: { type: 'album', id: 7, label: 'Abbey Road' },
+    });
+
+    expect(queueStore.getState().source).toEqual({
+      type: 'album',
+      id: 7,
+      label: 'Abbey Road',
+    });
+  });
+});
+
 describe('queue store: mode deltas', () => {
   beforeEach(() => {
     sync([track(1)], 0);