Schema-aware diff between two exported .policy.json files: top-level field changes, payload deep-diff, agent_instructions additions and removals, and stage-level diff for composite mandates matched by tool_id.
Tier 1: a Policy Mandate whose payload is the complete diff record: field changes, payload diff, agent_instructions delta, and stage diffs where applicable. mandate_type: compliance_control (closest existing enum per CONTRACT §3.1; flagged as a potential CONTRACT amendment candidate for a dedicated diff type).