feat(todo): wire up browser sync with Go server

- Auth store starts/stops sync on login/logout
- LocalStore queues all existing records for initial sync (guest→auth transition)
- LocalCollection.queueAllForSync() creates pending inserts for all local records
- Skips initial queue if sync cursor exists (already synced before)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/todo/apps/web/src/lib/stores/auth.svelte.ts

@@ -6,6 +6,7 @@
 import { browser } from '$app/environment';
 import { initializeWebAuth, type UserData } from '@manacore/shared-auth';
 import { apiClient } from '$lib/api/client';
+import { todoStore } from '$lib/data/local-store';
 
 // Default URLs for local development only
 const DEV_AUTH_URL = 'http://localhost:3001';
@@ -221,6 +222,9 @@ export const authStore = {
 				apiClient.setAccessToken(token);
 			}
 
+			// Start syncing local data to server
+			todoStore.startSync(() => authStore.getValidToken());
+
 			return { success: true };
 		} catch (error) {
 			const errorMessage = error instanceof Error ? error.message : 'Unknown error';
@@ -264,6 +268,9 @@ export const authStore = {
 	 * Sign out
 	 */
 	async signOut() {
+		// Stop syncing before clearing auth
+		todoStore.stopSync();
+
 		const authService = getAuthService();
 		if (!authService) {
 			user = null;

packages/local-store/src/collection.ts

@@ -281,6 +281,30 @@ export class LocalCollection<T extends BaseRecord> {
 		return this._table.where('updatedAt').above(since).toArray();
 	}
 
+	/**
+	 * Queue all existing local records as pending inserts.
+	 * Used for initial sync after login — ensures guest data gets pushed to server.
+	 */
+	async queueAllForSync(): Promise<number> {
+		const allRecords = await this._table.filter((r) => !r.deletedAt).toArray();
+		let count = 0;
+
+		await this._db.transaction('rw', [this._db._pendingChanges], async () => {
+			for (const record of allRecords) {
+				await this._db._pendingChanges.add({
+					collection: this.name,
+					recordId: record.id,
+					op: 'insert',
+					data: record as unknown as Record<string, unknown>,
+					createdAt: new Date().toISOString(),
+				});
+				count++;
+			}
+		});
+
+		return count;
+	}
+
 	// ─── Internal ───────────────────────────────────────────────
 
 	private async _trackChange(

packages/local-store/src/store.ts

@@ -147,7 +147,10 @@ export class LocalStore {
 			this._syncEngine.registerCollection(col);
 		}
 
-		this._syncEngine.start();
+		// Queue existing local data for initial sync (guest → authenticated transition)
+		this._queueInitialSync().then(() => {
+			this._syncEngine?.start();
+		});
 	}
 
 	/**
@@ -203,6 +206,33 @@ export class LocalStore {
 		await this.db.reset();
 	}
 
+	/**
+	 * Queue all existing local records for sync if this is the first sync.
+	 * Handles the guest→authenticated transition: local data gets pushed to server.
+	 */
+	private async _queueInitialSync(): Promise<void> {
+		// Check if we've synced before — if any collection has a cursor, skip
+		for (const [name] of this._collections) {
+			const cursor = await this.db.getSyncCursor(name);
+			if (cursor !== '1970-01-01T00:00:00.000Z') {
+				// Already synced before — pending changes from writes will handle it
+				return;
+			}
+		}
+
+		// First sync: queue all local records as pending inserts
+		let total = 0;
+		for (const col of this._collections.values()) {
+			const count = await col.queueAllForSync();
+			total += count;
+		}
+
+		if (total > 0) {
+			// eslint-disable-next-line no-console
+			console.log(`[LocalStore] Queued ${total} local records for initial sync`);
+		}
+	}
+
 	/**
 	 * Close the database connection.
 	 */