- Create FeatureStateManager class for feature status updates
- Extract updateFeatureStatus, markFeatureInterrupted, resetStuckFeatures
- Extract updateFeaturePlanSpec, saveFeatureSummary, updateTaskStatus
- Persist BEFORE emit pattern for data integrity (Pitfall 2)
- Handle corrupted JSON with readJsonWithRecovery backup support
- Preserve pipeline_* statuses in markFeatureInterrupted
- Fix bug: version increment now checks old content before applying updates
- Add 33 unit tests covering all state management operations
