Attaches a file to a launch run as evidence. Stage the file first with POST /v1/uploads (passing the run’s workspaceId) and a PUT to the returned URL, then pass the returned key here as uploadKey. The file moves into launch attachment storage and the staged upload is deleted. The response url is a permanent no-login link a pull request can embed. Retrying with the same uploadKey returns the same attachment with 200. Files are kept for 30 days and may be at most 104857600 bytes; encrypted uploads are refused.