feat(web/m7-364): queue persistence write/restore on player store

web/src/lib/player/store.svelte.ts

@@ -1,5 +1,7 @@
 import type { TrackRef, RadioResponse } from '$lib/api/types';
 import { api } from '$lib/api/client';
+import { user } from '$lib/auth/store.svelte';
+import { readPersistedQueue, writePersistedQueue } from './persisted';
 
 export type PlayerState = 'idle' | 'loading' | 'playing' | 'paused' | 'error';
 export type RepeatMode = 'off' | 'all' | 'one';
@@ -319,6 +321,20 @@ export function closeQueueDrawer(): void {
   _queueDrawerOpen = false;
 }
 
+export function restoreQueue(userId: string): void {
+  if (!userId) return;
+  const persisted = readPersistedQueue(userId);
+  if (!persisted) return;
+  if (persisted.queue.length === 0) return;
+  _queue = persisted.queue;
+  _index = Math.max(0, Math.min(persisted.index, persisted.queue.length - 1));
+  _position = persisted.position;
+  _duration = 0;
+  _state = 'paused';
+  _error = null;
+  _radioSeedId = null;
+}
+
 // M4c: auto-refresh radio queue when 80% consumed.
 // Fires whenever the consumption ratio crosses 80% AND the queue was
 // seeded by playRadio() AND no refresh is currently in-flight.
@@ -355,3 +371,45 @@ $effect.root(() => {
       });
   });
 });
+
+// Persistence (M7 #364): split-effect shape. Queue/index changes write
+// immediately (rare, user-driven); position changes throttle to once
+// per 5s during steady playback. See spec section "Persistence write
+// effect" for the alternative debounce shape.
+$effect.root(() => {
+  let lastPositionWriteAt = 0;
+
+  // Immediate write on queue or index changes.
+  $effect(() => {
+    const userId = user.value?.id;
+    if (!userId) return;
+    // Read these to register the dependency. Position is also read but
+    // its standalone changes are handled by the second effect below.
+    const _q = _queue;
+    const _i = _index;
+    void _q;
+    void _i;
+    writePersistedQueue(userId, {
+      queue: _queue,
+      index: _index,
+      position: _position
+    });
+    lastPositionWriteAt = Date.now();
+  });
+
+  // Throttled write on position changes.
+  $effect(() => {
+    const userId = user.value?.id;
+    if (!userId) return;
+    const _p = _position;
+    void _p;
+    const now = Date.now();
+    if (now - lastPositionWriteAt < 5000) return;
+    writePersistedQueue(userId, {
+      queue: _queue,
+      index: _index,
+      position: _position
+    });
+    lastPositionWriteAt = now;
+  });
+});