artifact: testing/deterministic/src/test/kotlin/RouterFacadeTest.kt
purpose: Test RouterFacade — verify end-to-end orchestration for both CHAT and STEERING modes using faked dependencies.
depends_on: task-013, task-019
non_goals: Testing individual components, testing WebSocket protocol
done_when: All facade tests pass with ./gradlew :testing:deterministic:test --tests RouterFacadeTest
