Verify the final path, not only canary selection

A canary smoke must distinguish cohort selection from successful experimental execution. Record both the selected path and final path: an application may choose the canary yet silently fall back when downstream name resolution or transport fails. Before treating an HTTP success as canary health, preflight the fixed origin from the same runtime, inspect DNS/transport evidence, and require final-path metadata. Afterward, revert allocation and verify the running consumer observed rollback using the same deterministic cohort key. This validates routing and transport, not model accuracy, which still requires independently labeled completed samples.

Applies when: A fallback-capable service is released behind percentage-based deterministic routing. Keywords: canary smoke fallback DNS final path rollout rollback cohort