# VEX merge explanation

## Module
VexLens

## Status
IMPLEMENTED

## Description
Consensus rationale models and service expose the reasoning behind VEX merge decisions from the consensus engine.

## Implementation Details
- **Rationale models**: `src/VexLens/StellaOps.VexLens/Api/ConsensusRationaleModels.cs` -- consensus rationale data models explaining merge decisions
- **Rationale service**: `src/VexLens/StellaOps.VexLens/Api/IConsensusRationaleService.cs` -- service interface for querying merge explanations
- **Rationale cache**: `src/VexLens/StellaOps.VexLens/Caching/IConsensusRationaleCache.cs` -- caches rationale for repeated queries
- **Delta report**: `src/VexLens/StellaOps.VexLens/Delta/DeltaReport.cs`, `DeltaReportBuilder.cs`, `DeltaEntry.cs`, `DeltaSection.cs` -- builds reports explaining what changed between VEX merge rounds
- **VEX delta mapper**: `src/VexLens/StellaOps.VexLens/Mapping/VexDeltaMapper.cs` -- maps delta changes to explanation models
- **VEX delta compute**: `src/VexLens/StellaOps.VexLens/Services/VexDeltaComputeService.cs` -- computes deltas between consensus rounds
- **Proof builder**: `src/VexLens/StellaOps.VexLens/Proof/VexProofBuilder.cs` -- includes merge reasoning in proof artifacts
- **Tests**: `src/VexLens/__Tests/StellaOps.VexLens.Tests/Delta/DeltaReportBuilderTests.cs`, `StellaOps.VexLens/__Tests/StellaOps.VexLens.Tests/Caching/ConsensusRationaleCacheTests.cs`
- **Source**: Feature matrix scan

## E2E Test Plan
- [ ] Verify rationale service explains why specific VEX status was chosen
- [ ] Test delta report identifies changes between consensus rounds
- [ ] Verify rationale cache returns consistent results
- [ ] Test merge explanation includes source weights and trust scores
- [ ] Verify proof artifacts contain merge reasoning