Task 03: Message Parity Harness
Summary
Parity validation between legacy message formats and canonical representations is incomplete. Without full parity coverage, there is limited confidence that adapter behavior matches real session data.
Context
tests/unit/types/test_adapter.py includes limited parity checks and round-trip coverage, but tests/parity/test_message_parity.py does not exist. There is no validation against real historical session artifacts.