## Summary
- Operators could see more agents running than Global Max Concurrent
(e.g. 5 running with cap 4: 4 planners + 1 executor).
- Scheduler now `tryAcquire`s a shared semaphore slot before
todo→in-progress and hands that pre-held slot to the executor/graph run.
- Triage admits planners against the live top-level running-agent claim
(planning + in-progress + active in-review), not only
`semaphore.availableCount`.
- Executor claims the pre-held slot for the full run and avoids a second
top-level acquire on step/seam re-entry (deadlock under a full cap).
## Test plan
- [x] `pnpm --filter @fusion/engine exec vitest run
src/__tests__/concurrency.test.ts src/__tests__/triage.test.ts`
- [x] Regression: triage leaves room when 1 in-progress agent is live
under global cap 4
- [x] Regression: pre-held executor slot register/take/drop handoff
- [ ] Manual: set Global Max Concurrent and Max triage concurrent to 4,
fill Planning + run 1 In Progress; footer should not show 5 running
under a full steady state
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## Summary by CodeRabbit
- **Bug Fixes**
- Improved global concurrency enforcement so the scheduler and executor
never start more agents than the configured limit, including tighter
top-level “claimed capacity” accounting.
- Updated triage admission control to consider global top-level
utilization, factoring processing tasks and agents already running to
prevent over-admitting planners.
- Added safer pre-held concurrency-slot handoff behavior to avoid
capacity leaks and drift during graph routing, step execution, and
legacy fallback.
- Ensured reserved capacity is reliably released on early exits, failed
dispatches, and other aborted paths (with idempotent cleanup).
- Refreshed concurrency diagnostics to better explain whether throttling
is due to project or global limits, with clearer claimed/processing
visibility.
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