complexity: surface the close error when the step-summary write fails

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Stefan Haubold4d ago

The write error still takes precedence; errors.Join carries the close error alongside it instead of discarding it (CodeQL go/unhandled-writable-file-close).

Co-Authored-By: Claude Fable 5 noreply@anthropic.com Entire-Checkpoint: 01M6EBSKGD55A90C22HE0J5N0R