feat(#1165): async external_job_waiting half-state + resume/pause contract (#1221)

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.

tests/workflow-size-baseline.json

@@ -24,8 +24,8 @@
   "docs-update.md": 54770,
   "edit-phase.md": 12883,
   "eval-review.md": 9923,
-  "execute-phase.md": 92961,
-  "execute-plan.md": 29980,
+  "execute-phase.md": 93142,
+  "execute-plan.md": 31365,
   "explore.md": 10497,
   "extract-learnings.md": 12849,
   "fast.md": 4149,
@@ -49,7 +49,7 @@
   "next.md": 17868,
   "node-repair.md": 4173,
   "note.md": 6563,
-  "pause-work.md": 13654,
+  "pause-work.md": 14397,
   "plan-milestone-gaps.md": 11765,
   "plan-phase.md": 92120,
   "plan-review-convergence.md": 22949,
@@ -61,7 +61,7 @@
   "reapply-patches.md": 20393,
   "remove-phase.md": 8469,
   "remove-workspace.md": 7507,
-  "resume-project.md": 15288,
+  "resume-project.md": 17226,
   "review.md": 38031,
   "scan.md": 7688,
   "secure-phase.md": 12282,