The root error fallback was one unbounded scroller, so on a phone the title
rendered under the status bar and a long stack trace pushed Retry off the
bottom of the screen — the one action that recovers the app was unreachable
on exactly the errors that need it most.
The screen is now a fixed shell: a safe-area message block, an independently
scrolling details region, and a Retry that stays put. `SafeAreaProvider` moved
above the boundary in the root tree because the fallback renders when the app
tree below it has already failed, and insets have to be available there.
The hand-rolled Pressable and bordered message box are replaced by the shared
`<Button>` and `<ScrollableCodeSurface>`, which gives the trace a monospace
face and horizontal scrolling instead of wrapping mid-token. On desktop the
trace is capped and the action sits with the message; a button pinned to the
bottom of a tall window reads as detached from the content it belongs to.
Dropped the "Something went wrong" kicker — it restated the title one line
above it.
