When a task is retried (dequeued again after failure), the previous
error message was persisting in the work_queue table. This caused the
API to return confusing responses with status="running" but also
containing an error message from the previous attempt.
Now clears error and completed_at when claiming a task, matching the
fix already applied to build_audit.UpdateStatus.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
59aa173384