host: verify dispatch completion snapshot and guard freshness invariants

[eggplantiny]

Context

Derived from the 2026-04-25 and 2026-04-28 Claude Code usage review.

Claude Code observed stale-state behavior around dispatch listeners and rapid dispatch gating. Current SPEC expectations suggest the runtime should provide a fresh completed snapshot and evaluate guards against the current dequeued snapshot.

Current assessment

SPEC status: provided, but implementation/adapters may be non-compliant or easy to misuse.

dispatch:completed should carry the fresh terminal snapshot. Guard/admission checks for queued or rapid dispatch should evaluate against the current snapshot at processing/dequeue time, not against stale React state or enqueue-time projections.

Desired outcome

Add compliance coverage and implementation audit for dispatch completion and guard freshness invariants.

Acceptance criteria

• Tests verify dispatch:completed includes the fresh terminal snapshot payload.
• Tests verify rapid sequential dispatch uses current/dequeue-time state for dispatchability or guard evaluation.
• Adapter examples avoid reading React-mediated stale state inside dispatch lifecycle listeners.
• If implementation is already compliant, docs/tests make the intended usage unambiguous.