fix(tools): single ordered driver lane for the sub-dispatch scheduler; validate the cap

Responding to ds-review-bot round 2 on #658 (three critical findings, one
warning — all rooted in the pump/commit split racing ordered stages):

- ONE driver lane now owns every ordered stage: the start append, prepare
  (pre-execute/guards), and the head-of-line commit (post-execute, context
  deferral, settle append). start() is awaited before the next entry can
  start, so concurrent submissions can no longer run pre-execute pipelines
  concurrently; only the around-dispatch/body stage overlaps, matching the
  native loop's fillPool sequencing.
- An exclusive call's barrier now holds through its COMMIT: later starts
  wait for the exclusive pipeline (post-execute included) to finish, the
  native exclusive-group semantics.
- drainDispatches() awaits the driver run itself, so a commit already
  mid-flight when the program returns is drained before run_code closes
  the turn — the settle event and deferred contexts land inside it.
- maxParallelSubCalls is resolved and validated at construction (positive
  integer), so direct construction can no longer wedge the pool with 0.

New tests: overlapping-submission ordered-prepare, barrier-through-commit,
drain-mid-commit, cap rejection. 96 keyless snapshots replay unchanged;
Agent Note updated (both languages).

.agents/notes/implemented/feature/2026-07-26-code-mode-live-parallel-dispatch.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write
-2026-07-26-code-mode-live-parallel-dispatch.md: f0d13456d63779fb89b9af4cb09bc90c37356a21
-2026-07-26-code-mode-live-parallel-dispatch.zh.md: 5554ab0456f13a2bbc6d5b18e515930f954c6682
+2026-07-26-code-mode-live-parallel-dispatch.md: b4afc21be902d8ed3e5bee2ad1a540413a864f25
+2026-07-26-code-mode-live-parallel-dispatch.zh.md: 409e4cbf9ea3d1b4d1bbe0cd86b494429ebb8a3d