Goalpost: v19 test-law and serialization paydown

[flyingrobots]

Thesis slice

Pay down the test-law and serialization-owner debt that can slip only if the generated boundary and domain-leak goalposts prove the v19 release thesis without it.

Owns

• Ban conditional early returns in test bodies #429
• WarpGraph.audit.test.js has vacuous tests with conditional early returns #256
• Domain types own their own serialization (P5 violation) #385
• CborCheckpointStoreAdapter owns general CRDT serialization #379
• Coverage ratchet baseline dropped during v17 release preflight #261
• PROTO_trust-record-service-unreachable-exhausted-tails #237

Acceptance evidence

• Vacuous audit tests are made fail-loud or the blocking cases are moved to a later milestone with rationale.
• Conditional early-return test policy is either implemented or explicitly cut.
• Domain-owned serialization and checkpoint/CRDT serialization extraction are completed or moved forward with scope notes.
• Coverage ratchet paydown has evidence or a documented deferral.