## Summary
- Fix a false-positive in `StuckTaskDetector` where legitimate long
single-step work (E2E debugging, iterative fix/test cycles) was
classified as a loop and kill/requeued.
- Root cause: loop meant “no step status transition for
`taskStuckTimeoutMs` + high activity volume,” conflating **step
progress** with **actual activity**. Agents can stay productively busy
on one step for 10+ minutes with zero repetition.
- Loop now requires thrash evidence on top of volume + no step progress:
- **repetitive tool fingerprints** (`toolName` + primary-arg detail in a
sliding window), or
- **elevated ignored step-update rebuffs** (≥ 10)
- Wire tool name/detail from `AgentLogger` → executor / step-session
into `recordActivity(...)` so novelty is measurable.
- Document the thrash-evidence rule in `docs/architecture.md`.
## Test plan
- [x] `pnpm --filter @fusion/engine exec vitest run
src/__tests__/stuck-task-detector.test.ts
src/__tests__/reliability-interactions/non-progress-churn.test.ts`
- [x] Regression: high-volume **diverse** iterative activity (174
events) does **not** classify as loop
- [x] High bare text/heartbeat volume without tools does **not**
classify as loop
- [x] Repetitive identical tool fingerprint + timeout **does** classify
as loop
- [x] Ignored step-update thrash (≥10) with volume **does** classify as
loop
- [x] Existing FN-5168 no-progress-churn + FN-6598 verification
suppression paths still pass
- [ ] CI gate green
<!-- This is an auto-generated comment: release notes by coderabbit.ai
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## Summary by CodeRabbit
* **Bug Fixes**
* Improved stuck/loop classification by requiring explicit “thrash
evidence” (repetitive tool fingerprints and/or elevated ignored progress
rebuffs), reducing false positives for busy but diverse work.
* Updated loop evidence tracking to incorporate tool name plus
summarized tool-argument detail.
* Cleared loop evidence appropriately after verification, progress
updates, and task resumption.
* Extended tool-start telemetry/callbacks to include optional tool
detail.
* **Documentation**
* Refined loop-classification criteria to match the new evidence gates.
* **Tests**
* Updated/expanded stuck/loop and churn scenarios to validate the
evidence-based behavior and callback ordering.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
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