Operation marker for proposing a Change Request without applying it immediately. The operation records a proposed change under proposal state so another participant or policy-controlled workflow can later accept or reject it. Propose Change is used when a document requires review, approval, negotiation, or human consent before applying a mutation. The request shape is Workflows/Change Request, including a summary and optional structured sectionChanges. The operation itself only declares the action; the paired Propose Change Workflow implements storage and validation.