feat(services): server kind for the playlist storage backend

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/services/src/lib/playlist-storage-backend.spec.ts

@@ -41,4 +41,30 @@ describe('PlaylistStorageBackend', () => {
         expect(backend.kind()).toBe('indexeddb');
         expect(backend.documentStore()).toBeNull();
     });
+
+    it('prefers the server store once it is set', () => {
+        testWindow.electron = undefined;
+        const backend = create(false);
+        const store = { dbGetAppPlaylists: jest.fn() } as never;
+
+        backend.useServerStore(store);
+
+        expect(backend.kind()).toBe('server');
+        expect(backend.documentStore()).toBe(store);
+    });
+
+    it('falls back to browser storage while an override task runs', async () => {
+        testWindow.electron = undefined;
+        const backend = create(false);
+        backend.useServerStore({ dbGetAppPlaylists: jest.fn() } as never);
+
+        const seen = await backend.runWithBrowserStorage(async () => [
+            backend.kind(),
+            backend.usesBrowserStorageOverride(),
+        ]);
+
+        expect(seen).toEqual(['indexeddb', true]);
+        expect(backend.kind()).toBe('server');
+        expect(backend.usesBrowserStorageOverride()).toBe(false);
+    });
 });

libs/services/src/lib/playlist-storage-backend.ts

@@ -28,20 +28,51 @@ export type PlaylistDocumentStore = Pick<
         >
     >;
 
-export type PlaylistStorageKind = 'electron' | 'indexeddb';
+export type PlaylistStorageKind = 'electron' | 'server' | 'indexeddb';
 
 /** Single place that decides where `PlaylistsService` persists playlists. */
 @Injectable({ providedIn: 'root' })
 export class PlaylistStorageBackend {
     private readonly runtime = inject(RuntimeCapabilitiesService);
+    private serverStore: PlaylistDocumentStore | null = null;
+    private browserOverrideDepth = 0;
+
+    /** Server mode: set once by the server storage session at startup. */
+    useServerStore(store: PlaylistDocumentStore): void {
+        this.serverStore = store;
+    }
+
+    usesBrowserStorageOverride(): boolean {
+        return this.browserOverrideDepth > 0;
+    }
+
+    /**
+     * Runs `task` against browser storage although server mode is active.
+     * Only the migration export uses it, inside a modal flow.
+     */
+    async runWithBrowserStorage<T>(task: () => Promise<T>): Promise<T> {
+        this.browserOverrideDepth += 1;
+        try {
+            return await task();
+        } finally {
+            this.browserOverrideDepth -= 1;
+        }
+    }
 
     kind(): PlaylistStorageKind {
+        if (this.serverStore && this.browserOverrideDepth === 0) {
+            return 'server';
+        }
         return this.runtime.supportsSqlite ? 'electron' : 'indexeddb';
     }
 
     /** The document store for `kind()`, or `null` for IndexedDB. */
     documentStore(): PlaylistDocumentStore | null {
-        if (this.kind() !== 'electron' || typeof window === 'undefined') {
+        const kind = this.kind();
+        if (kind === 'server') {
+            return this.serverStore;
+        }
+        if (kind !== 'electron' || typeof window === 'undefined') {
             return null;
         }
         return (window.electron as PlaylistDocumentStore | undefined) ?? null;