fix(dynamic-workflow): deterministic wait polling and checkpoint lineage in repair reuse

[modacker]

What changes

Three small correctness fixes for plugins/hetaoBackend/mcode-dynamic-workflows (merged via #42), split out so each is reviewable on its own.

1. Deterministic review-loop polling (checks/workspace-router.check.mjs): the wait loop called workflow_wait without afterSequence. waitEvents returns immediately whenever any event exists after the cursor (src/tools.mjs), and with after=0 events always exist — so all 30 iterations burned in ~65 ms on a warm machine while the run needed ~66 ms. The outcome is decided by IPC latency: we reproduced both a failure and a pass on the same machine at the same commit. The loop now advances status.nextSequence, so each call blocks up to 500 ms for a genuinely new event; the worst case stays bounded (30 × 500 ms).

2. Checkpoint lineage in repair reuse (src/engine.mjs): the candidate lineage check required every dependency to carry reusedFrom.runId === sourceRunId. Checkpoints recompute every run by design and never carry reusedFrom, so any agent step with a checkpoint in dependsOn silently fell back to a fresh (billable) call even when the candidate was valid. Checkpoint dependencies now accept the recomputed step when its requestHash matches the source run's checkpoint; a changed checkpoint value still invalidates downstream reuse. A regression test covers both directions.

3. Dead code (src/engine.mjs): removed the second byRequest(requestId) lookup in start() — unreachable, since the first lookup returns for any existing request and nothing writes the store in between (no await point). For the record: we initially also flagged the trailing re-check in resume() as redundant — wrong; it is the TOCTOU guard after the fingerprints await, and the "simultaneous resumes launch only one replay" test caught our mistake before this PR was filed.

dist/main.mjs is rebuilt from the changed engine; the build remains byte-reproducible.

Verification

• node --test checks/*.check.mjs: 73/73 (72 existing + 1 new checkpoint-lineage test)
• node --test test/package.test.mjs: pass
• Repository npm run check (clean checkout, plugin node_modules removed): green
• workspace-router check after the fix: 3/3 runs pass (previously intermittent)
• macOS arm64, Node v26.7.0, based on the plugin as merged in Add Dynamic Workflow: visual review, execution, and script repair #42

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[modacker]

Related design discussion for the repair-reuse machinery in this PR: #46 (tamper-evident reuse results). No action needed on this PR — the issue is a forward-looking proposal.