refactor(playback): move the audio engine into features/playback

Relocate the playback/queue/transport/audio-output engine out of the type-first
store/ + utils/playback/ + utils/audio/ dirs into a cohesive src/features/playback/,
structure-preserving:
  store/<x>                    -> features/playback/store/<x>
  store/audioListenerSetup/<x> -> features/playback/store/audioListenerSetup/<x>
  utils/playback/<x>           -> features/playback/utils/playback/<x>
  utils/audio/<x>              -> features/playback/utils/audio/<x>

184 files moved (107 source + 77 tests), 365 consumers rewritten. Pure move — no
behavior change, no state-split (the playerStore state-split stays a separate M5
question). Enabled by this session's decouple seams (artist/offline/orbit/auth →
core registries), so the engine carries no inbound core->feature inversion: store/
now holds only the 50 cross-cutting global stores (auth family, the seams, library
index, UI/settings stores).

KEPT OUT of the move (would re-create global->engine edges): the 3 pure config
helpers utils/audio/{loudnessPreAnalysisSlider,hiResCrossfadeResample} +
utils/playback/autodjOverlapCap (authStore + settings UI read them — they stay in
utils/). Ambiguous view-state stores (eqStore, queueToolbarStore,
playerBarLayoutStore) stay global (no engine imports).

Consumers use DEEP paths (@/features/playback/...), no barrel — matches the lib/
approach and avoids barrel-mock-collapse across the 140 usePlayerStore consumers.
Two tolerated type-only core->feature edges remain (localPlaybackStore->QueueItemRef,
localPlaybackMigration->HotCacheEntry, both erased).

tsc 0, lint 0, full suite 319/2353 green, iron-rule clean (no runtime store->feature
import). Behavior-touching only via the prerequisite bridge seam (already QA-flagged);
the move itself is pure.

src/features/playlist/components/PlaylistArtistCell.tsx

@@ -1,7 +1,7 @@
 import React, { useMemo } from 'react';
 import { useNavigate } from 'react-router-dom';
 import type { SubsonicSong } from '@/lib/api/subsonicTypes';
-import { resolveTrackArtistRefs } from '@/utils/playback/trackArtistRefs';
+import { resolveTrackArtistRefs } from '@/features/playback/utils/playback/trackArtistRefs';
 
 /**
  * Multi-artist credit for playlist track rows (main list + suggestions).

src/features/playlist/components/PlaylistCard.tsx

@@ -3,7 +3,7 @@ import { useTranslation } from 'react-i18next';
 import { useNavigate } from 'react-router-dom';
 import { Check, Clock3, ListMusic, Pencil, Play, Sparkles, Trash2 } from 'lucide-react';
 import type { SubsonicPlaylist } from '@/lib/api/subsonicTypes';
-import { usePlayerStore } from '@/store/playerStore';
+import { usePlayerStore } from '@/features/playback/store/playerStore';
 import {
   displayPlaylistName, isSmartPlaylistName, type PendingSmartPlaylist,
 } from '@/features/playlist/utils/playlistsSmart';

src/features/playlist/components/PlaylistSongSearchPanel.tsx

@@ -2,8 +2,8 @@ import React from 'react';
 import { useTranslation } from 'react-i18next';
 import { Check, ListPlus, X } from 'lucide-react';
 import type { SubsonicSong } from '@/lib/api/subsonicTypes';
-import { usePlayerStore } from '@/store/playerStore';
-import { songToTrack } from '@/utils/playback/songToTrack';
+import { usePlayerStore } from '@/features/playback/store/playerStore';
+import { songToTrack } from '@/features/playback/utils/playback/songToTrack';
 import { formatTrackTime } from '@/lib/format/formatDuration';
 import { AlbumCoverArtImage } from '@/cover/AlbumCoverArtImage';
 import { COVER_DENSE_SEARCH_CSS_PX } from '@/cover/layoutSizes';

src/features/playlist/components/PlaylistSuggestions.tsx

@@ -4,13 +4,13 @@ import { useNavigate } from 'react-router-dom';
 import { ChevronRight, Heart, Play, Plus, RefreshCw, Square } from 'lucide-react';
 import type { ColDef } from '@/utils/useTracklistColumns';
 import type { SubsonicSong } from '@/lib/api/subsonicTypes';
-import { usePlayerStore } from '@/store/playerStore';
-import { usePreviewStore } from '@/store/previewStore';
+import { usePlayerStore } from '@/features/playback/store/playerStore';
+import { usePreviewStore } from '@/features/playback/store/previewStore';
 import StarRating from '@/components/StarRating';
 import { PlaylistArtistCell } from '@/features/playlist/components/PlaylistArtistCell';
 import { useThemeStore } from '@/store/themeStore';
 import { usePlaylistLayoutStore } from '@/features/playlist/store/playlistLayoutStore';
-import { songToTrack } from '@/utils/playback/songToTrack';
+import { songToTrack } from '@/features/playback/utils/playback/songToTrack';
 import { getQueueTracksView } from '@/utils/library/queueTrackView';
 import { codecLabel } from '@/utils/componentHelpers/playlistDetailHelpers';
 import { formatLastSeen } from '@/utils/componentHelpers/userMgmtHelpers';

src/features/playlist/components/PlaylistTracklist.tsx

@@ -11,13 +11,13 @@ import {
 } from 'lucide-react';
 import type { ColDef } from '@/utils/useTracklistColumns';
 import type { SubsonicSong } from '@/lib/api/subsonicTypes';
-import type { Track } from '@/store/playerStoreTypes';
-import { usePlayerStore } from '@/store/playerStore';
-import { previewInputFromSong, usePreviewStore } from '@/store/previewStore';
+import type { Track } from '@/features/playback/store/playerStoreTypes';
+import { usePlayerStore } from '@/features/playback/store/playerStore';
+import { previewInputFromSong, usePreviewStore } from '@/features/playback/store/previewStore';
 import { useThemeStore } from '@/store/themeStore';
 import { useDragDrop } from '@/lib/dnd/DragDropContext';
 import { useOrbitSongRowBehavior } from '@/features/orbit';
-import { songToTrack } from '@/utils/playback/songToTrack';
+import { songToTrack } from '@/features/playback/utils/playback/songToTrack';
 import type { PlaylistSortKey, PlaylistSortDir } from '@/features/playlist/utils/playlistDisplayedSongs';
 import { AddToPlaylistSubmenu } from '@/components/ContextMenu';
 

src/features/playlist/hooks/usePlaylistBulkPlayCallbacks.ts

@@ -1,5 +1,5 @@
 import { useCallback } from 'react';
-import type { Track } from '@/store/playerStoreTypes';
+import type { Track } from '@/features/playback/store/playerStoreTypes';
 import { enqueuePlaylistAll, playPlaylistAll, shufflePlaylistAll } from '@/features/playlist/utils/playlistBulkPlayActions';
 
 export interface PlaylistBulkPlayCallbacksDeps {

src/features/playlist/hooks/usePlaylistDerived.ts

@@ -1,8 +1,8 @@
 import { useMemo } from 'react';
 import type { SubsonicSong } from '@/lib/api/subsonicTypes';
-import type { Track } from '@/store/playerStoreTypes';
-import { usePlayerStore } from '@/store/playerStore';
-import { songToTrack } from '@/utils/playback/songToTrack';
+import type { Track } from '@/features/playback/store/playerStoreTypes';
+import { usePlayerStore } from '@/features/playback/store/playerStore';
+import { songToTrack } from '@/features/playback/utils/playback/songToTrack';
 import { getDisplayedSongs, type PlaylistSortDir, type PlaylistSortKey } from '@/features/playlist/utils/playlistDisplayedSongs';
 
 export interface PlaylistDerivedOptions {

src/features/playlist/hooks/usePlaylistPreview.ts

@@ -1,5 +1,5 @@
 import { useCallback, useEffect } from 'react';
-import { previewInputFromSong, usePreviewStore } from '@/store/previewStore';
+import { previewInputFromSong, usePreviewStore } from '@/features/playback/store/previewStore';
 import type { SubsonicSong } from '@/lib/api/subsonicTypes';
 
 export function usePlaylistPreview(): {

src/features/playlist/hooks/usePlaylistRouteEffects.ts

@@ -1,6 +1,6 @@
 import React, { useEffect } from 'react';
 import type { Location, NavigateFunction } from 'react-router-dom';
-import { usePlayerStore } from '@/store/playerStore';
+import { usePlayerStore } from '@/features/playback/store/playerStore';
 
 export interface PlaylistRouteEffectsDeps {
   setContextMenuSongId: React.Dispatch<React.SetStateAction<string | null>>;

src/features/playlist/hooks/usePlaylistStarRating.ts

@@ -1,7 +1,7 @@
 import React from 'react';
-import { queueSongStar, queueSongRating } from '@/store/pendingStarSync';
+import { queueSongStar, queueSongRating } from '@/features/playback/store/pendingStarSync';
 import type { SubsonicSong } from '@/lib/api/subsonicTypes';
-import { usePlayerStore } from '@/store/playerStore';
+import { usePlayerStore } from '@/features/playback/store/playerStore';
 
 export interface PlaylistStarRatingDeps {
   ratings: Record<string, number>;

src/features/playlist/pages/PlaylistDetail.tsx

@@ -3,7 +3,7 @@ import type { SubsonicPlaylist, SubsonicSong } from '@/lib/api/subsonicTypes';
 import React, { useEffect, useState, useCallback, useMemo } from 'react';
 import { useParams, useNavigate, useLocation } from 'react-router-dom';
 import { useTracklistColumns, type ColDef } from '@/utils/useTracklistColumns';
-import { usePlayerStore } from '@/store/playerStore';
+import { usePlayerStore } from '@/features/playback/store/playerStore';
 import { useShallow } from 'zustand/react/shallow';
 import { usePlaylistStore } from '@/features/playlist/store/playlistStore';
 import { useOfflineStore } from '@/features/offline';

src/features/playlist/pages/Playlists.tsx

@@ -2,9 +2,9 @@ import { resolveMediaServerId, resolvePlaylist } from '@/features/offline';
 import { getGenres } from '@/lib/api/subsonicGenres';
 import { filterSongsToActiveLibrary } from '@/lib/api/subsonicLibrary';
 import type { SubsonicPlaylist, SubsonicGenre } from '@/lib/api/subsonicTypes';
-import { songToTrack } from '@/utils/playback/songToTrack';
+import { songToTrack } from '@/features/playback/utils/playback/songToTrack';
 import React, { useEffect, useState, useRef, useCallback } from 'react';
-import { usePlayerStore } from '@/store/playerStore';
+import { usePlayerStore } from '@/features/playback/store/playerStore';
 import { usePlaylistStore } from '@/features/playlist/store/playlistStore';
 import { useAuthStore } from '@/store/authStore';
 import { useTranslation } from 'react-i18next';

src/features/playlist/utils/playPlaylistById.ts

@@ -1,6 +1,6 @@
 import { getPlaylist } from '@/lib/api/subsonicPlaylists';
-import { songToTrack } from '@/utils/playback/songToTrack';
-import { usePlayerStore } from '@/store/playerStore';
+import { songToTrack } from '@/features/playback/utils/playback/songToTrack';
+import { usePlayerStore } from '@/features/playback/store/playerStore';
 import { playPlaylistAll } from '@/features/playlist/utils/playlistBulkPlayActions';
 
 /**

src/features/playlist/utils/playlistBulkPlayActions.test.ts

@@ -1,6 +1,6 @@
 import { describe, expect, it, vi } from 'vitest';
 import { enqueuePlaylistAll, playPlaylistAll, shufflePlaylistAll } from '@/features/playlist/utils/playlistBulkPlayActions';
-import type { Track } from '@/store/playerStoreTypes';
+import type { Track } from '@/features/playback/store/playerStoreTypes';
 
 // Only id/queue identity matters for these actions.
 const tracks = [{ id: 'a' }, { id: 'b' }, { id: 'c' }] as unknown as Track[];

src/features/playlist/utils/playlistBulkPlayActions.ts

@@ -1,4 +1,4 @@
-import type { Track } from '@/store/playerStoreTypes';
+import type { Track } from '@/features/playback/store/playerStoreTypes';
 
 // No `touchPlaylist` here: playing/shuffling/enqueuing does not modify the
 // playlist. Touching it bumps `lastModified`, which is the playlist detail

src/features/playlist/utils/startPlaylistRowDrag.ts

@@ -1,6 +1,6 @@
 import type React from 'react';
 import type { SubsonicSong } from '@/lib/api/subsonicTypes';
-import { songToTrack } from '@/utils/playback/songToTrack';
+import { songToTrack } from '@/features/playback/utils/playback/songToTrack';
 
 export interface StartPlaylistRowDragDeps {
   e: React.MouseEvent;