F11: US3 — Routing Visibility (Phase 5) #120
Description
User Story
Operators can see why Nexus selected a particular backend via route_reason field.
Priority: P2
Depends on: #117 (Foundation — needs route_reason in RoutingResult)
Tests (TDD — Red Phase)
- T110-T112: Route reason format tests
Implementation (Green Phase)
- T032-T038: Routing strategy reason strings
Acceptance Criteria
- route_reason populated for all routing strategies
- Fallback scenarios explained in route_reason