## Summary
- Closes#61
- Replaces #62, which was opened from a branch that still carried the drawer commit already merged in #60 and therefore conflicted. Same change, cherry-picked cleanly onto current `master`.
- **Makes the mobile white screen diagnosable.** The app had **no error boundary anywhere**, so any throw in the dashboard unmounted the whole tree and left an empty `#root`. That matches the reported behavior exactly: brief flash, white page, other routes fine on a fresh load, blank again when navigating back to `/`. `AppErrorBoundary` renders the error name, message, stack, URL and user agent with Reload / Copy details buttons, so the real exception can be read and copied **from the phone**. It is keyed on the route path, so navigating away clears a crash.
- **Responsive layout fixes** for the clipping visible in mobile emulation: `100vw` → `100%`, `100dvh` for the chat shell so mobile URL bars can't push the input row off screen, `min-width: 0` / `flex-shrink` on the input row so attach, model select, textarea and send compress instead of overflowing, `env(safe-area-inset-*)` padding on header, drawer and input area, and message bubbles that wrap long tokens (`overflow-wrap: anywhere`, `max-width` on `pre`/`img`/`table`).
- **Perf:** particle canvas pauses while the tab is hidden, honors `prefers-reduced-motion`, caps particle count for the O(n²) link pass, and re-seeds only on real size changes. Chat auto-scroll now fires on message change rather than on every render.
## Test plan
- [x] `npm run test:ci` — 25 suites / 112 tests pass (adds `AppErrorBoundary` coverage for the pass-through and crash paths)
- [x] `npm run build` — clean
- [ ] Phone browser: sign in and land on `/` — chat renders, or the error card shows the real exception (paste into #61)
- [ ] Phone browser: no horizontal scroll; attach, model select, textarea and send all visible
- [ ] Phone browser: input row still reachable with the keyboard open
- [ ] Long code block / unbroken string stays inside the bubble
- [ ] Desktop: sidebar, chat and input unchanged; background animation still runs
- [ ] Background the tab and return — animation resumes
## Notes
The crash is not reproducible in desktop mobile emulation, so this ships the boundary as the diagnostic path instead of guessing at the throwing call site. Once the error card appears on the phone, the stack should point straight at the cause. Worth landing before the Capacitor Android wrap (#20), since the same failure mode is much harder to inspect inside a WebView.Reviewed-on: #63
westfarn
f22441371b
