# VEX-First Gating Service (Pre-Triage Filter)

## Module
Scanner

## Status
VERIFIED

## Description
Pre-triage VEX gating service that filters vulnerability findings before reaching triage queue. Gate decisions (Pass/Warn/Block) with 4 default rules (block-exploitable-reachable, warn-high-not-reachable, pass-vendor-not-affected, pass-backport-confirmed). Includes caching observation provider, performance benchmarks, scan pipeline stage integration, bypass for emergency scans, and audit logging.

## Implementation Details
- **VEX Gate Service**:
  - `src/Scanner/__Libraries/StellaOps.Scanner.Gate/VexGateService.cs` - `VexGateService` pre-triage filter evaluating VEX gate rules and producing Pass/Warn/Block decisions
  - `src/Scanner/__Libraries/StellaOps.Scanner.Gate/IVexGateService.cs` - Interface for VEX gate operations
  - `src/Scanner/__Libraries/StellaOps.Scanner.Gate/VexGateResult.cs` - `VexGateResult` capturing gate decision with rule match details
  - `src/Scanner/__Libraries/StellaOps.Scanner.Gate/VexGateDecision.cs` - `VexGateDecision` enum (Pass, Warn, Block)
- **Policy Evaluation**:
  - `src/Scanner/__Libraries/StellaOps.Scanner.Gate/VexGatePolicyEvaluator.cs` - `VexGatePolicyEvaluator` evaluating the 4 default rules against findings
  - `src/Scanner/__Libraries/StellaOps.Scanner.Gate/VexGatePolicy.cs` - `VexGatePolicy` defining gate rules (block-exploitable-reachable, warn-high-not-reachable, pass-vendor-not-affected, pass-backport-confirmed)
- **Caching Observation Provider**:
  - `src/Scanner/__Libraries/StellaOps.Scanner.Gate/CachingVexObservationProvider.cs` - `CachingVexObservationProvider` caching VEX observation lookups for performance
- **Configuration**:
  - `src/Scanner/__Libraries/StellaOps.Scanner.Gate/VexGateOptions.cs` - `VexGateOptions` configuration including emergency bypass settings
- **Excititor Adapter**:
  - `src/Scanner/__Libraries/StellaOps.Scanner.Gate/VexGateExcititorAdapter.cs` - Adapter integrating with the Excititor VEX feed service
- **Audit Logging**:
  - `src/Scanner/__Libraries/StellaOps.Scanner.Gate/VexGateAuditLogger.cs` - `VexGateAuditLogger` logging all gate decisions for audit trail
- **Pipeline Integration**:
  - `src/Scanner/StellaOps.Scanner.Worker/Processing/VexGateStageExecutor.cs` - `VexGateStageExecutor` scan pipeline stage executing VEX gate evaluation
- **WebService**:
  - `src/Scanner/StellaOps.Scanner.WebService/Controllers/VexGateController.cs` - `VexGateController` REST API for gate queries and overrides
  - `src/Scanner/StellaOps.Scanner.WebService/Services/VexGateQueryService.cs` - Service for querying gate decisions
  - `src/Scanner/StellaOps.Scanner.WebService/Contracts/VexGateContracts.cs` - API contracts
- **DI Registration**:
  - `src/Scanner/__Libraries/StellaOps.Scanner.Gate/VexGateServiceCollectionExtensions.cs` - DI registration for gate services
- **Tests**:
  - `src/Scanner/__Tests/StellaOps.Scanner.Gate.Tests/VexGateServiceTests.cs` - VEX gate service unit tests
  - `src/Scanner/__Tests/StellaOps.Scanner.Gate.Tests/VexGatePolicyEvaluatorTests.cs` - Policy evaluator tests
  - `src/Scanner/__Tests/StellaOps.Scanner.WebService.Tests/VexGateEndpointsTests.cs` - API endpoint tests
  - `src/Scanner/__Tests/StellaOps.Scanner.Worker.Tests/VexGateStageExecutorTests.cs` - Pipeline stage tests

## E2E Test Plan
- [ ] Submit a finding with exploitable-reachable status and verify the gate blocks it (block-exploitable-reachable rule)
- [ ] Submit a high-severity finding that is not reachable and verify the gate warns (warn-high-not-reachable rule)
- [ ] Submit a finding with vendor VEX "not_affected" and verify the gate passes it (pass-vendor-not-affected rule)
- [ ] Submit a finding with confirmed backport and verify the gate passes it (pass-backport-confirmed rule)
- [ ] Verify emergency scan bypass correctly skips gate evaluation when configured
- [ ] Verify `CachingVexObservationProvider` caches VEX lookups and performance is within benchmarked thresholds
- [ ] Verify audit logging captures all gate decisions with rule match details and timestamps

---

## 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 |