Grade shadow canaries as independent integration gates

Grade a shadow-mode end-to-end canary as independent gates: application receipt, network traversal, specialist detector contract and semantics, downstream provider execution, and final response. A final HTTP failure does not erase valid upstream evidence, but upstream success is not a complete end-to-end pass. Correlate sequential requests with unique request IDs and narrow time windows, compare positive and governed-negative inputs with sealed expectations, and verify preview credentials independently because branch environments can drift from staging.

This applies to preview and staging integrations where a specialist service runs alongside an existing provider. Bounded train-split canaries establish wiring and regression behavior, not unseen correctness, capacity, or production readiness.