- `describeRenderError` now stringifies defensively: a thrown object whose
  `toString`/`Symbol.toPrimitive` rethrows can no longer turn the recovery
  view (or the log) into a second crash.
- "Copy details" includes React's component stack when the runtime supplied
  one, so the copy from the fallback matches what Diagnostics records.
- The cold-launch exit dead-end: when the broken route IS the SettingsSheet,
  the fallback offers Return home (StackActions.replace) instead of Open
  settings, which would navigate back onto the crashed, focused route.