def normalize(case):
    """Return a dict with channel, raw_message_ref, external_message_id, source_system,
    occurred_at, received_at, participant_handles, thread_hint, body_ref, attachment_refs,
    normalization_version, provenance_pointer, dedupe_key, dedupe_state, delivery_action,
    parse_state, unsupported_fields, ingest_decision, identity_state, and reason.

    Derive the result from visible synthetic evidence. Keep identity unresolved and preserve
    replay/unsupported states instead of silently converting them into success.
    """
    raise NotImplementedError("Implement the source-preserving normalization contract")