- subagents.history computes its projections best-effort on both arms
(a hostile unit's fold rejection serves the page without the block,
matching the session-list precedent) with dual-arm coverage
- the lifecycle-witness spec probes every field of the seven-key
witness, protecting the key list itself
- list-children's own module docs catch up with the seq-gate contract,
and the design note records the rung-two later-event window as an
accepted, self-healing deviation of the corruption class