Retrying.Generate returned the earlier provider error (e.g. a 429) when
cancellation or the deadline interrupted the backoff wait, so callers and
the ai_runs record saw rate limiting instead of cancellation. Return the
context error from the interrupted wait instead. Retry counts, backoff and
other error semantics are unchanged.
Maestro task: 79447ef7-e55c-4641-b351-37bc22ffa760
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>