a98431a12a
- Protocol: StartNodePayload.parentState, StateNodePayload.childThread - CAS: putStartNode refs include parentState, collectRefs includes childThread - Parsing: legacy nodes without new fields default to null - Engine + fork: all callers pass parentState: null / childThread: null - Tests: 8 new cases for refs, parsing, collect-refs (+208 lines) Phase 1 of #194 (Merkle Call Stack). Closes #195. 小橘 <xiaoju@shazhou.work>