Two root causes:
1. In-flight test: resolveFetch() was the last line, leaving the async
finally-block writing `training = false` after cleanup destroyed the
component. Awaiting the button becoming re-enabled ensures the finally
block settles before cleanup runs.
2. Success-dismiss test: startTraining() schedules setTimeout(5000) which
fired after cleanup destroyed the component. vi.useFakeTimers() +
vi.runAllTimers() scoped to the describe block drains the timer while
the component is still alive.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
