* fix(app): keep focused agent timelines live
Window focus was conflated with app visibility, so switching OS windows could remove the selected timeline subscription. Separate those signals, grace every visibility-driven removal, and cover retained history until authoritative catch-up completes.
* fix(app): keep timeline catch-up failures non-blocking
* fix(app): surface timeline catch-up failures
* fix(app): preserve file preview refocus
* fix(app): preserve optimistic catch-up flow
Add `packages/app/src/constants/platform.ts` with canonical gates
(isWeb, isNative, getIsElectron) and refactor all ~100 ad-hoc
Platform.OS checks across 69 files to use shared imports.
Fix sidebar hover crash on native (onPointerEnter → onHoverIn),
fix tooltip to use breakpoint instead of platform detection, make
sidebar action buttons always visible on native where hover doesn't
work, and document the platform gating decision matrix in CLAUDE.md.
Multiple clients viewing the same terminal would fight over PTY size
because every client sent resizes independently. Gate resize sends on
three focus levels: pane focus (split panes), screen focus (navigation),
and app visibility (browser window / mobile foreground). When a client
regains focus, clear the last reported size and trigger a reflow to
reclaim the PTY dimensions.
