approvalId

Approval-identity key. Mirrors v6's approvalId (per historical parity gap #7). Distinct from toolCallId because multiple approvals can share a toolCallId (e.g., parallel tool-call batches where the model emits one tool-call with the SAME id twice and each side needs separate approval). When null, the host treats approvalId = toolCallId — adequate for the common single-approval case.