A 404 on /messages is protocol-path evidence.Do not rotate a valid key before proving which stream implementation built the request.

Route the construction decision.

Catalog id + no api

Reuse the catalog provider and delegate its stream implementation.

Catalog id + api

Build the supported protocol explicitly, replacing catalog dispatch.

New id + no api

Reject the route because no protocol owner exists.

New id + api

Build an independently named custom provider.

Prove the final path.

OpenAI Completions/chat/completions

Requires api: openai-completions for an intentional custom route.

OpenAI Responses/responses

Different request and response contract; do not infer it from the URL.

Anthropic Messages/messages

May come from an explicit protocol or a reused catalog provider.

Prefer a distinct application-owned provider id.

Keep Sessions, defaults, credentials, logs, and rollback unambiguous. Record the sanitized final path in a fresh Session.

Backward-compatible hardening.

Catalog reuse must remain available for native authentication and compatibility behavior. Authoring surfaces should warn when a catalog id combines an omitted protocol with a changed endpoint, and tests must assert the final wire path—not only the model list.

Keep the complete recovery matrix.

The canonical guide includes safe YAML, supported protocols, request evidence, credential boundaries, acceptance gates, and rollback.

Read the complete guide