# Evolution: DES US-008 - Session-Scoped Stale Execution Detection

**Project ID**: des-us008-stale-detection
**Completed**: 2026-01-31
**Wave**: DELIVER
**Duration**: ~4 hours (orchestrated)

## Summary

Implemented session-scoped stale execution detection for the Distributed Execution System (DES) to automatically detect and block execution when IN_PROGRESS phases exceed a configurable threshold (default 30 minutes). The solution uses pure file scanning without external dependencies and provides a resolution mechanism to mark stale steps as ABANDONED.

## Key Achievements

### Implementation Highlights

1. **Domain Layer** (Hexagonal Architecture - Core)
   - `StaleExecution`: Immutable value object representing a single stale execution with business validation
   - `StaleDetectionResult`: Domain entity aggregating multiple stale executions with blocking logic

2. **Application Layer** (Use Cases)
   - `StaleExecutionDetector`: Service for scanning steps directory and detecting stale executions (threshold configurable via environment variable)
   - `StaleResolver`: Service to mark stale steps as ABANDONED with recovery suggestions

3. **Orchestrator Integration**
   - Pre-execution hook in `DESOrchestrator.execute_step_with_stale_check()`
   - Blocks execution when stale detected (is_blocked=true)
   - Displays alert with step_file, phase_name, age_minutes
   - Provides resolution instructions

### Technical Decisions

- **Pure File Scanning**: Zero external dependencies (no DB, HTTP, daemon processes)
- **Session-Scoped**: Detection runs before each `/nw:execute`, terminates with session
- **Configurable Threshold**: Default 30 minutes, overridable via `DES_STALE_THRESHOLD_MINUTES`
- **Graceful Degradation**: Handles corrupted JSON files with warnings, continues scan
- **Boundary-Exclusive Comparison**: Fixed threshold logic bug (>= changed to >) during step 02-02

## Metrics

### Implementation Scope

| Metric | Value |
|--------|-------|
| Steps Completed | 13 |
| Phases Executed (8-phase TDD) | 104 (13 × 8) |
| Total Duration | ~134 minutes (~10 min/step avg) |
| Commits Created | 13 (one per step) |

### Code Artifacts

| Artifact Type | Count | Lines of Code |
|---------------|-------|---------------|
| Domain Classes | 2 | 195 |
| Application Services | 2 | 230 |
| Unit Tests | 51 | ~800 |
| Acceptance Tests | 11 | ~400 |
| **Total Implementation** | **4 files** | **425 LOC** |
| **Total Tests** | **62 tests** | **~1200 LOC** |

### Quality Gates Passed

| Gate | Result |
|------|--------|
| Roadmap Review (software-crafter-reviewer) | ✅ Approved (1st attempt) |
| All Acceptance Tests (11 scenarios) | ✅ 11/11 passing |
| All Unit Tests (51 tests) | ✅ 51/51 passing |
| Mutation Testing (75% threshold) | ✅ 82.84% kill rate (140/169) |
| TDD Phase Tracking | ✅ 104/104 phases completed |

### Mutation Testing Results

Per-component kill rates:
- `stale_execution.py`: 90.91% (10/11)
- `stale_detection_result.py`: 79.17% (19/24)
- `stale_execution_detector.py`: 90.10% (91/101)
- `stale_resolver.py`: 60.61% (20/33) ⚠️
- **Aggregate**: 82.84% (140/169) ✅

## Key Decisions Made

1. **Threshold Logic**: Use boundary-exclusive comparison (> not >=) to avoid false positives at exact threshold
2. **Environment Variable Parsing**: Implemented robust validation with try/except and positive value check
3. **Error Handling**: Corrupted files generate warnings (file_path + error message) but don't crash scan
4. **Resolution Mechanism**: ABANDONED status automatically excluded from future stale detection scans
5. **Metadata Documentation**: Added `uses_external_services=False` and `is_session_scoped=True` properties

## Architectural Patterns

- **Hexagonal Architecture**: Domain → Application → Infrastructure (orchestrator integration)
- **Outside-In TDD**: Started from acceptance tests, drove implementation from domain outward
- **Immutable Value Objects**: StaleExecution is frozen dataclass with __post_init__ validation
- **Pure Functions**: scan_for_stale_executions() has no side effects (reads files, returns result)
- **Dependency Inversion**: Orchestrator depends on StaleExecutionDetector abstraction

## Lessons Learned

1. **Boundary Conditions Matter**: Original `>=` comparison incorrectly flagged phases exactly at threshold
2. **Test Quality !== Test Coverage**: Mutation testing revealed gaps in stale_resolver.py despite 100% line coverage
3. **Session-Scoped > Daemon**: Synchronous file scanning simpler and more reliable than background processes
4. **Progressive Complexity**: Started with simple domain objects, added complexity incrementally through TDD

## Future Enhancements

1. **Improve stale_resolver.py Coverage**: Add tests for 13 surviving mutants (currently 60.61% kill rate)
2. **Configurable Alert Format**: Allow customization of alert message template
3. **Stale Execution History**: Track historical stale detection events for analysis
4. **Auto-Resolution Options**: Configurable policy for automatic ABANDONED marking after N detections

## Files Created/Modified

### Implementation Files

1. `src/des/domain/stale_execution.py` (72 LOC)
2. `src/des/domain/stale_detection_result.py` (123 LOC)
3. `src/des/application/stale_execution_detector.py` (142 LOC)
4. `src/des/application/stale_resolver.py` (88 LOC)
5. `src/des/application/orchestrator.py` (modified - added execute_step_with_stale_check)

### Test Files

1. `tests/des/unit/test_stale_execution.py`
2. `tests/des/unit/test_stale_detection_result.py`
3. `tests/des/unit/test_stale_execution_detector.py`
4. `tests/des/unit/test_stale_resolver.py`
5. `tests/des/unit/application/test_orchestrator_stale_check.py`
6. `tests/des/acceptance/test_us008_stale_detection.py` (11 scenarios)

## Workflow Artifacts (Archived)

- `docs/feature/des-us008-stale-detection/roadmap.yaml` (11 steps across 5 phases)
- `docs/feature/des-us008-stale-detection/execution-log.yaml` (13 completed steps)
- `docs/feature/des-us008-stale-detection/mutation/mutation-report.md` (82.84% kill rate)

## Integration Points

- **DES Orchestrator**: Pre-execution stale check hook
- **Environment Variables**: `DES_STALE_THRESHOLD_MINUTES` (optional override)
- **Execution Status Files**: Reads IN_PROGRESS phases from `docs/feature/{project-id}/execution-log.yaml`

## Acceptance Criteria Validation

All 11 acceptance criteria met:

✅ AC-008.1: Pre-execution scan detects stale execution
✅ AC-008.2: Clean start when no stale executions
✅ AC-008.3: Recent IN_PROGRESS within threshold not stale
✅ AC-008.4: Custom threshold via environment variable
✅ AC-008.5: Alert includes step, phase, and age details
✅ AC-008.6: Resolve stale step unblocks new execution
✅ AC-008.7: Mark step ABANDONED updates state correctly
✅ AC-008.8: Pure file scanning (no external dependencies)
✅ AC-008.9: No persistent daemon after check completes
✅ AC-008.10: Multiple stale executions all reported
✅ AC-008.11: Corrupted step file gracefully handled

## Next Steps

1. **DELIVER Wave**: Deploy stale detection to production DES environment
2. **Monitoring**: Track stale detection frequency and false positive rate
3. **Follow-up**: Address 13 surviving mutants in stale_resolver.py to reach 90%+ kill rate

---

**Methodology**: Outside-In TDD with Hexagonal Architecture
**Total Quality Gates**: 1 roadmap review + 104 TDD phase reviews + 1 mutation testing gate
**Test-to-Code Ratio**: ~2.8:1 (1200 LOC tests / 425 LOC implementation)
**Feature Ready**: Production-ready, all quality gates passed
