fix( frontend) :notification permission refresh - #3768

Fixes #3767

Why

Browser notifications could be skipped after a user enabled notification permission in Settings.

The root cause is that useNotification() stores permission state per hook instance. When Settings requests permission, another hook instance used by the chat/agent page can still hold the stale "default" state and refuse to send notifications until the page is refreshed.

There was also a first-notification timing edge case: lastNotificationTime was initialized at hook creation time, so a valid notification sent immediately after the hook mounted could be incorrectly throttled.

What changed

• Notification sending now reads the browser's current Notification.permission before deciding whether to send.
• The hook syncs its local permission state if the browser permission has changed.
• First notification throttling now only applies after a notification has actually been sent.
• Added unit tests covering:
  • first notification can be sent immediately;
  • rate limiting starts only after a successful send;
  • browser permission changes from another hook instance are respected.
• Added Playwright coverage for notification settings/test-notification behavior.
• Added an accessible label to the notification settings switch.

Surface area

• Frontend UI — page / component / setting / interaction under frontend/
• Backend API — endpoint / SSE event / request-response shape under backend/app
• Agents / LangGraph — agent node, graph wiring, langgraph.json, or prompt change
• Sandbox — docker/ or sandboxed execution
• Skills — change under skills/
• Dependencies — new/upgraded entry in backend/pyproject.toml or frontend/package.json (say what it buys us)
• Default behavior change — notifications now use the browser's latest permission state when sending
• Docs / tests / CI only — no runtime behavior change

Screenshots / Recording

N/A. This is a notification behavior fix; the visible Settings UI is unchanged.

Bug fix verification

Test path that reproduces the bug:

• frontend/tests/unit/core/notification/hooks.test.ts

Before the fix, the notification hook tests fail against the old behavior:

• the first notification can be rejected as Notification sent too soon;
• a hook instance can keep stale "default" permission after another hook grants browser permission.

After the fix, the same tests pass.

Validation

cd frontend && pnpm test tests/unit/core/notification/hooks.test.ts
cd frontend && pnpm typecheck

AI assistance

Tool(s) used: codex

How you used it: AI helps with testing and code review.

• I've read and understand every line of this change and take responsibility for it — it's not unreviewed AI output.