Event emitted when a proposed, accepted, rejected, or direct change request cannot be processed under the document's change-management rules. The event communicates a deterministic reason such as missing summary, missing proposal, duplicate proposal, forbidden `/contracts` mutation, malformed sectionChanges, or another validation failure. This event is intended to be observable by users, agents, and audit tools. It signals that the requested change did not become document state. The `reason` field should be human-readable and stable enough for diagnostics, but it is not a substitute for the processor's formal error category when the processor itself terminates fatally.