## Summary
- Hook the bottom bar up to react-native-screens' transition progress. Every `Layout.Screen` now exposes a `presence` shared value (via `useScreenPresence`) that follows the native push/pop/swipe frame by frame, so screens with `minimalShell` hide and reveal the bar in sync with the transition instead of after it. Fixes the delayed tab bar when leaving a conversation.
- Replace the minimal-shell and hide-border refcounts with a small registry that sums 0..1 contributions on the UI thread. The bottom bar border now fades with the screen rather than toggling.
- Bring back the scroll-linked bottom bar on Home (removed in #5203). The header and footer share the same drag-linked value, and the bar is revealed on feed change, blur, and app foreground so badges aren't missed. Web included.
## Test plan
- [ ] Swipe back from a conversation: bar tracks the swipe, including a cancelled swipe
- [ ] Back button from a conversation: bar animates with the pop
- [ ] Push a profile over a conversation and pop back
- [ ] Post thread: bottom bar border fades in/out with the screen
- [ ] Home: scroll down hides header and bar together, scroll up shows them
- [ ] Home: scrolled down, swipe into a convo and back - no jump
- [ ] Home: bar reappears on feed switch, on leaving Home, and on foregrounding the app
- [ ] Deep link / notification into a conversation from another tab
- [ ] Mobile web: bar hides/shows on scroll and on conversation screen
- [ ] Rapid swipe-back and swipe-back while scrolling (software-mansion/react-native-reanimated#9402, software-mansion/react-native-screens#2659)
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JWQciPDiipBhqiW922Nivs
Claude
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