# Backport FixIndex Service with O(1) Distro Patch Lookups

## Module
Concelier

## Status
VERIFIED

## Description
Indexed distro patch lookup service providing O(1) performance for determining whether a specific package version contains a backported fix for a given CVE across multiple distributions.

## Implementation Details
- **Modules**: `src/Concelier/__Libraries/StellaOps.Concelier.BackportProof/`
- **Key Classes**:
  - `FixIndexService` (`src/Concelier/__Libraries/StellaOps.Concelier.BackportProof/Services/FixIndexService.cs`) - O(1) indexed lookup for distro patch status
  - `BackportStatusService` (`src/Concelier/__Libraries/StellaOps.Concelier.BackportProof/Services/BackportStatusService.cs`) - backport status resolution with version comparison
  - `BackportEvidenceResolver` (`src/Concelier/__Libraries/StellaOps.Concelier.Merge/Backport/BackportEvidenceResolver.cs`) - multi-tier evidence resolution consuming fix index data
- **Interfaces**: `IFixIndexService`, `IBackportStatusService`
- **Source**: SPRINT_20251229_004_002_BE_backport_status_service.md

## E2E Test Plan
- [ ] Query `FixIndexService` for a known CVE+distro+package combination and verify it returns patch status in O(1)
- [ ] Verify `BackportStatusService` correctly compares package versions to determine if a backport fix is present
- [ ] Verify cross-distro lookups: query the same CVE for Alpine, Debian, and RedHat and verify correct fix status for each
- [ ] Verify index population: ingest distro connector data and verify the fix index is populated
- [ ] Verify negative case: query for a CVE with no known backport fix and verify "unknown" or "not fixed" status