Presence, display, and click routing#

Remote checks whether the user is already viewing a chat before showing an alert. The backend handles other devices; the service worker handles the receiving device.

flowchart LR Event["Notification ready"] --> ServerCheck["Watching on any device?"] ServerCheck -->|"Yes"| Stop["Suppress"] ServerCheck -->|"No"| Push["Send to device"] Push --> LocalCheck["Chat visible here?"] LocalCheck -->|"Yes"| Stop LocalCheck -->|"No"| Show["Show notification"] Show --> Open["Open chat on click"]

Backend presence#

The focused page reports its user, page-local client ID, and visible chat. It refreshes that claim every 20 seconds. The backend considers the claim valid for 55 seconds.

Claims are tracked per browser tab so one background tab cannot cancel another focused tab's presence. Every claim, heartbeat, and release carries a monotonically increasing revision. The backend accepts only the newest revision for that tab and retains releases as bounded tombstones, so a delayed older claim cannot revive presence.

Presence lives only in memory; a backend restart may cause an extra notification but does not lose durable application state.

Service-worker check#

After receiving a push, the service worker asks visible windows which chat is focused. It waits up to 400 milliseconds:

a matching chat suppresses the notification;
no matching response displays it.

The worker favors an extra alert over silently losing one. Its only offline cache entry is the self-contained /offline.html navigation fallback; it does not cache the app shell, API responses, or project data.

Notification display#

Question notifications request stronger attention through high urgency, interaction persistence, and vibration where supported. Notifications use a tag based on the chat ID, so a newer alert for the same chat replaces the old one.

Click routing#

If a Remote window exists, the worker focuses it and sends an open-chat message.
If no window exists, the worker opens /?chat=<id>.
During cold startup, the application consumes that query parameter and selects the requested chat.