changelog.d/4879-assignment-refusal-evidence.md

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- **Blocked cross-crew delegations now leave an audit receipt.** Activity and the run journal identify the calling agent, source and target crew, and the server's link-check refusal, while storing only a digest of the task. Cross-crew acceptance verifies a real Ops record, joins completion to the original assignment, and requires a server refusal for the unlinked case.