# OCI Layer Manifest Infrastructure for Delta Scanning

## Module
Scanner

## Status
VERIFIED

## Description
Infrastructure for OCI manifest snapshotting with layer digest resolution and diffID-based layer tracking. Provides layer reuse detection across image versions and a registry client abstraction to support delta scanning workflows. Distinct from generic "OCI Ancestry Extraction" in known features.

## Implementation Details
- **Manifest Snapshot Service**:
  - `src/Scanner/__Libraries/StellaOps.Scanner.Manifest/IOciManifestSnapshotService.cs` - `IOciManifestSnapshotService` interface for manifest snapshot operations
  - `src/Scanner/__Libraries/StellaOps.Scanner.Manifest/OciManifestSnapshotService.cs` - `OciManifestSnapshotService` captures and compares OCI manifest snapshots for delta scanning
- **Manifest Models**:
  - `src/Scanner/__Libraries/StellaOps.Scanner.Manifest/Models/OciManifestSnapshot.cs` - `OciManifestSnapshot` representing a point-in-time manifest state with layer digests
  - `src/Scanner/__Libraries/StellaOps.Scanner.Manifest/Models/ManifestComparisonResult.cs` - `ManifestComparisonResult` identifies added, removed, and unchanged layers between snapshots
- **Layer Digest Resolution**:
  - `src/Scanner/__Libraries/StellaOps.Scanner.Manifest/Resolution/ILayerDigestResolver.cs` - Interface for resolving layer digests to diffIDs
  - `src/Scanner/__Libraries/StellaOps.Scanner.Manifest/Resolution/LayerDigestResolver.cs` - `LayerDigestResolver` resolves compressed layer digests to uncompressed diffIDs for consistent tracking
- **Layer Reuse Detection**:
  - `src/Scanner/__Libraries/StellaOps.Scanner.Manifest/Reuse/LayerReuseDetector.cs` - `LayerReuseDetector` identifies unchanged layers across image versions to skip re-analysis
- **Persistence**:
  - `src/Scanner/__Libraries/StellaOps.Scanner.Manifest/Persistence/IManifestSnapshotRepository.cs` - Repository interface for snapshot storage
  - `src/Scanner/__Libraries/StellaOps.Scanner.Manifest/Persistence/ManifestSnapshotRepository.cs` - PostgreSQL-backed snapshot persistence
- **DI Registration**: `src/Scanner/__Libraries/StellaOps.Scanner.Manifest/ManifestServiceCollectionExtensions.cs`

## E2E Test Plan
- [ ] Scan an image and verify a manifest snapshot is captured with all layer digests and diffIDs
- [ ] Rescan a newer version of the same image and verify manifest comparison correctly identifies added, removed, and unchanged layers
- [ ] Verify layer reuse detection skips unchanged layers in subsequent scans, reducing scan time
- [ ] Verify diffID-based tracking correctly matches layers across manifest versions despite compressed digest differences
- [ ] Verify manifest snapshots are persisted and retrievable for historical comparison

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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 |