# Model Version Change Detection

## Module
Scanner

## Status
VERIFIED

## Description
Change detection for EPSS model version updates that suppresses noisy deltas when the underlying model changes, preventing false signal cascades.

## Implementation Details
- **EPSS Model Version Tracking**:
  - `src/Scanner/__Libraries/StellaOps.Scanner.Storage/Epss/EpssCsvStreamParser.cs` - `EpssCsvStreamParser` detects model version tags (e.g., `v2024.01.15`) from EPSS CSV data feeds and tracks version changes
  - `src/Scanner/__Libraries/StellaOps.Scanner.Storage/Epss/EpssExplainHashCalculator.cs` - `EpssExplainHashCalculator` includes `ModelVersion` in explain hash calculations to distinguish model-driven vs real-world score changes
- **Change Detection**:
  - `src/Scanner/__Libraries/StellaOps.Scanner.Storage/Epss/EpssChangeDetector.cs` - `EpssChangeDetector` detects score changes between EPSS updates
  - `src/Scanner/__Libraries/StellaOps.Scanner.Storage/Epss/EpssChangeRecord.cs` - `EpssChangeRecord` model for recording detected changes with model version context
- **Events**:
  - `src/Scanner/__Libraries/StellaOps.Scanner.Storage/Epss/Events/EpssUpdatedEvent.cs` - `EpssUpdatedEvent` includes `ModelVersionTag` to flag model-version-driven updates
  - `src/Scanner/__Libraries/StellaOps.Scanner.Storage/Epss/EpssReplayService.cs` - `EpssReplayService` replays EPSS data with model version awareness for noise suppression

## E2E Test Plan
- [ ] Ingest two EPSS CSV feeds with the same model version and verify genuine score changes are detected
- [ ] Ingest an EPSS CSV feed with a new model version tag and verify the model version change is detected
- [ ] Verify that when a model version changes, score deltas are flagged as model-driven rather than generating false signal cascades
- [ ] Verify the explain hash includes model version so that model-change deltas are distinguishable from real-world changes
- [ ] Verify the replay service correctly handles model version transitions without generating spurious change events

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## Verification

| Check | Result |
|-------|--------|
| Tier 0 - Source files exist | PASS |
| Tier 1 - Build + code review | PASS |
| Tier 2 - Integration tests | PASS |
| Verified | 2026-02-13T18:10:00Z |