Metrics / Success Criteria

• New messages appear within 15 seconds of arrival (10s poll + 5s request)
• User at bottom sees new messages without manual action
• User scrolled up sees a visible indicator and can jump to bottom
• OSK input is never interrupted by polling
• No error screens during transient network failures
• Optimistic sends appear within 100ms of button press
• No duplicate messages visible after optimistic → confirmed transition
• Chat list shows unread indicators for non-active chats
• Battery life impact is negligible (<5% additional drain over 1 hour)