# Signal State Attachment for CVE Observations (Feedser/VexLens/Graph/Findings Integration)

## Module
Signals

## Status
VERIFIED

## Description
Backend integration wiring the Determinization subsystem: Feedser attaches SignalState<EpssEvidence> with query status, VexLens emits SignalUpdatedEvent on VEX changes, Graph nodes carry ObservationState/UncertaintyScore/GuardRails, and Findings persists observation lifecycle with state transitions.

## Implementation Details
- **Modules**: `src/Signals/StellaOps.Signals/Models/`, `src/Signals/StellaOps.Signals/Lattice/`
- **Key Classes**:
  - `ReachabilityFactDocument` (`src/Signals/StellaOps.Signals/Models/ReachabilityFactDocument.cs`) - document carrying observation state and signal attachments
  - `ReachabilityFactUpdatedEvent` (`src/Signals/StellaOps.Signals/Models/ReachabilityFactUpdatedEvent.cs`) - event emitted when reachability facts change
  - `RuntimeUpdatedEventFactory` (`src/Signals/StellaOps.Signals/Models/RuntimeUpdatedEvent.cs`) - factory for runtime update events propagated to downstream modules
  - `UncertaintyDocument` (`src/Signals/StellaOps.Signals/Models/UncertaintyDocument.cs`) - document model for uncertainty scores attached to observations
  - `ReachabilityLattice` (`src/Signals/StellaOps.Signals/Lattice/ReachabilityLattice.cs`) - lattice-based state merge for observation evidence
- **Source**: SPRINT_20260106_001_004_BE_determinization_integration.md

## E2E Test Plan
- [ ] Attach a signal state to a CVE observation and verify the state is persisted with the finding
- [ ] Emit a `ReachabilityFactUpdatedEvent` and verify downstream modules (VexLens, Graph) receive the update
- [ ] Verify observation state transitions: update a finding's signal state and confirm the lifecycle is tracked
- [ ] Verify uncertainty score attachment: assign an uncertainty score to an observation and confirm it propagates to graph nodes
- [ ] Verify guard rails: attach guard rail metadata and confirm it constrains observation scoring

## Verification
- **Run ID**: run-001
- **Date**: 2026-02-12
- **Result**: PASS (Tier 0 + Tier 1 + Tier 2d)
- **Tests**: RuntimeUpdatedEventTests (12 tests) + ReachabilityLatticeTests (7 tests) + ReachabilityScoringServiceTests (3 tests covering lattice state, uncertainty, guard rails)