🐛(frontend) fix broadcast store sync

When going from one subdoc to another by example,
the broadcast store could have difficulty to resync.
This commit ensures that the broadcast store
cleans up and resets its state when rerendering.
It will stop as well triggering the action for
the current user avoiding potential unecessary
requests.

CHANGELOG.md

@@ -6,6 +6,10 @@ and this project adheres to
 
 ## [Unreleased]
 
+### Fixed
+
+🐛(frontend) fix broadcast store sync #1846
+
 ## [v4.5.0] - 2026-01-28
 
 ### Added 

src/frontend/apps/e2e/__tests__/app-impress/doc-header.spec.ts

@@ -7,7 +7,12 @@ import {
   mockedDocument,
   verifyDocName,
 } from './utils-common';
-import { mockedAccesses, mockedInvitations } from './utils-share';
+import {
+  connectOtherUserToDoc,
+  mockedAccesses,
+  mockedInvitations,
+  updateShareLink,
+} from './utils-share';
 import { createRootSubPage, getTreeRow } from './utils-sub-pages';
 
 test.beforeEach(async ({ page }) => {
@@ -52,13 +57,54 @@ test.describe('Doc Header', () => {
     ).toBeVisible();
   });
 
-  test('it updates the title doc', async ({ page, browserName }) => {
-    await createDoc(page, 'doc-update', browserName, 1);
-    const docTitle = page.getByRole('textbox', { name: 'Document title' });
-    await expect(docTitle).toBeVisible();
-    await docTitle.fill('Hello World');
-    await docTitle.blur();
+  test('it updates the title doc and check the broadcast', async ({
+    page,
+    browserName,
+  }) => {
+    const [docTitle] = await createDoc(
+      page,
+      'doc-title-update',
+      browserName,
+      1,
+    );
+    await page.getByRole('button', { name: 'Share' }).click();
+    await updateShareLink(page, 'Public', 'Editing');
+
+    const docUrl = page.url();
+
+    const { otherPage, cleanup } = await connectOtherUserToDoc({
+      docUrl,
+      browserName,
+      withoutSignIn: true,
+      docTitle,
+    });
+
+    // Wait for other page to sync
+    await page.waitForTimeout(1000);
+
+    await page.keyboard.press('Escape');
+    const elTitle = page.getByRole('textbox', { name: 'Document title' });
+    await expect(elTitle).toBeVisible();
+    await elTitle.fill('Hello World');
+    await elTitle.blur();
     await verifyDocName(page, 'Hello World');
+
+    // Wait for other page to sync
+    await page.waitForTimeout(1000);
+
+    // Check other user page
+    await verifyDocName(otherPage, 'Hello World');
+
+    const elTitleOther = otherPage.getByRole('textbox', {
+      name: 'Document title',
+    });
+    await elTitleOther.fill('Hello Other World');
+    await elTitleOther.blur();
+
+    // Check first user page
+    await verifyDocName(page, 'Hello Other World');
+
+    await cleanup();
   });
 
   test('it updates the title doc adding a leading emoji', async ({

src/frontend/apps/impress/src/features/docs/doc-management/hooks/useCollaboration.tsx

@@ -8,7 +8,7 @@ import { Base64 } from '../types';
 
 export const useCollaboration = (room?: string, initialContent?: Base64) => {
   const collaborationUrl = useCollaborationUrl(room);
-  const { setBroadcastProvider } = useBroadcastStore();
+  const { setBroadcastProvider, cleanupBroadcast } = useBroadcastStore();
   const { provider, createProvider, destroyProvider } = useProviderStore();
 
   useEffect(() => {
@@ -33,8 +33,9 @@ export const useCollaboration = (room?: string, initialContent?: Base64) => {
   useEffect(() => {
     return () => {
       if (room) {
+        cleanupBroadcast();
         destroyProvider();
       }
     };
-  }, [destroyProvider, room]);
+  }, [destroyProvider, room, cleanupBroadcast]);
 };

src/frontend/apps/impress/src/stores/useBroadcastStore.tsx

@@ -5,7 +5,9 @@ import { create } from 'zustand';
 interface BroadcastState {
   addTask: (taskLabel: string, action: () => void) => void;
   broadcast: (taskLabel: string) => void;
+  cleanupBroadcast: () => void;
   getBroadcastProvider: () => HocuspocusProvider | undefined;
+  handleProviderSync: () => void;
   provider?: HocuspocusProvider;
   setBroadcastProvider: (provider: HocuspocusProvider) => void;
   setTask: (
@@ -15,11 +17,12 @@ interface BroadcastState {
   ) => void;
   tasks: {
     [taskLabel: string]: {
-      task: Y.Array<string>;
+      action: () => void;
       observer: (
         event: Y.YArrayEvent<string>,
         transaction: Y.Transaction,
       ) => void;
+      task: Y.Array<string>;
     };
   };
 }
@@ -27,7 +30,22 @@ interface BroadcastState {
 export const useBroadcastStore = create<BroadcastState>((set, get) => ({
   provider: undefined,
   tasks: {},
-  setBroadcastProvider: (provider) => set({ provider }),
+  setBroadcastProvider: (provider) => {
+    // Clean up old provider listeners
+    const oldProvider = get().provider;
+    if (oldProvider) {
+      oldProvider.off('synced', get().handleProviderSync);
+    }
+
+    provider.on('synced', get().handleProviderSync);
+    set({ provider });
+  },
+  handleProviderSync: () => {
+    const tasks = get().tasks;
+    Object.entries(tasks).forEach(([taskLabel, { action }]) => {
+      get().addTask(taskLabel, action);
+    });
+  },
   getBroadcastProvider: () => {
     const provider = get().provider;
     if (!provider) {
@@ -43,20 +61,16 @@ export const useBroadcastStore = create<BroadcastState>((set, get) => ({
       return;
     }
 
-    const existingTask = get().tasks[taskLabel];
-    if (existingTask) {
-      existingTask.task.unobserve(existingTask.observer);
-      get().setTask(taskLabel, existingTask.task, action);
-      return;
-    }
-
     const task = provider.document.getArray<string>(taskLabel);
     get().setTask(taskLabel, task, action);
   },
   setTask: (taskLabel: string, task: Y.Array<string>, action: () => void) => {
     let isInitializing = true;
-    const observer = () => {
-      if (!isInitializing) {
+    const observer = (
+      _event: Y.YArrayEvent<string>,
+      transaction: Y.Transaction,
+    ) => {
+      if (!isInitializing && !transaction.local) {
         action();
       }
     };
@@ -73,16 +87,27 @@ export const useBroadcastStore = create<BroadcastState>((set, get) => ({
         [taskLabel]: {
           task,
           observer,
+          action,
         },
       },
     }));
   },
   broadcast: (taskLabel) => {
+    // Broadcast via Y.js provider (for users on the same document)
     const obTask = get().tasks?.[taskLabel];
-    if (!obTask || !obTask.task) {
-      console.warn(`Task ${taskLabel} is not defined`);
-      return;
+    if (obTask?.task) {
+      obTask.task.push([`broadcast: ${taskLabel}`]);
     }
-    obTask.task.push([`broadcast: ${taskLabel}`]);
+  },
+  cleanupBroadcast: () => {
+    const provider = get().provider;
+    if (provider) {
+      provider.off('synced', get().handleProviderSync);
+    }
+
+    // Unobserve all document-specific tasks
+    Object.values(get().tasks).forEach(({ task, observer }) => {
+      task.unobserve(observer);
+    });
   },
 }));