Core half of #1105: a legal external_job_waiting deferred state so an async-dispatched Execute step (committing a .planning/async-jobs/<job>.json manifest, deferring SUMMARY.md) is not an illegal partial. execute-phase safe-resume, resume-project, and pause-work reconcile against the versioned scheduler-agnostic manifest stability contract without re-dispatching; the producer is the capability half (#1164). Closes#1165.