docs(browser-db-sqlite-persistence): document multi-tab coordinator usage

packages/browser-db-sqlite-persistence/README.md

@@ -1,14 +1,22 @@
 # @tanstack/browser-db-sqlite-persistence
 
-Thin browser SQLite persistence for TanStack DB using `wa-sqlite` + OPFS.
+Browser SQLite persistence for TanStack DB using `wa-sqlite` + OPFS.
+
+Supports both single-tab (default) and multi-tab usage. Multi-tab coordination
+is opt-in by passing a `BrowserCollectionCoordinator`.
 
 ## Public API
 
 - `createBrowserWASQLitePersistence(...)`
 - `openBrowserWASQLiteOPFSDatabase(...)`
 - `persistedCollectionOptions(...)` (re-exported from core)
 
-## Quick start
+## Quick start (single-tab)
+
+By default, `createBrowserWASQLitePersistence` uses `SingleProcessCoordinator`
+semantics — no leader election, no `BroadcastChannel`, no Web Locks. This is
+the right choice when your app is only ever open in one tab at a time, or when
+each tab uses its own database.
 
 ```ts
 import { createCollection } from '@tanstack/db'
@@ -42,13 +50,60 @@ export const todosCollection = createCollection(
 )
 ```
 
+## Multi-tab usage
+
+To safely share a single OPFS database across multiple tabs of the same
+origin, pass a `BrowserCollectionCoordinator` via the `coordinator` option.
+The coordinator uses the Web Locks API to elect a leader tab, and
+`BroadcastChannel` to fan out committed transactions to follower tabs.
+Follower tabs forward writes to the leader via RPC over the channel.
+
+```ts
+import { createCollection } from '@tanstack/db'
+import {
+  BrowserCollectionCoordinator,
+  createBrowserWASQLitePersistence,
+  openBrowserWASQLiteOPFSDatabase,
+  persistedCollectionOptions,
+} from '@tanstack/browser-db-sqlite-persistence'
+
+const database = await openBrowserWASQLiteOPFSDatabase({
+  databaseName: `tanstack-db.sqlite`,
+})
+
+const coordinator = new BrowserCollectionCoordinator({
+  dbName: `tanstack-db`,
+})
+
+const persistence = createBrowserWASQLitePersistence({
+  database,
+  coordinator,
+})
+
+export const todosCollection = createCollection(
+  persistedCollectionOptions<Todo, string>({
+    id: `todos`,
+    getKey: (todo) => todo.id,
+    persistence,
+    schemaVersion: 1,
+  }),
+)
+
+// On teardown:
+// coordinator.dispose()
+// await database.close?.()
+```
+
+See [`examples/react/offline-transactions`](../../examples/react/offline-transactions/src/db/persisted-todos.ts)
+for a full multi-tab example.
+
 ## Notes
 
-- This package is Phase 7 single-tab browser wiring: it uses
-  `SingleProcessCoordinator` semantics by default.
 - `openBrowserWASQLiteOPFSDatabase(...)` starts a dedicated Web Worker and
   routes SQL operations through it. OPFS sync access handle APIs are used in
   that worker context.
-- Single-tab mode does not require BroadcastChannel or Web Locks for
+- Single-tab mode does not require `BroadcastChannel` or Web Locks for
   correctness.
+- Multi-tab mode requires `BroadcastChannel` and the Web Locks API; both are
+  available in all modern browsers.
 - OPFS capability failures are surfaced as `PersistenceUnavailableError`.