fix(e2e): route credential, cost map, and UI login calls to the control plane (#42506)

* fix(e2e): route credential, cost map, and UI login calls to the control plane

* test(e2e): stop pinning the upstream model name in the credential-backed messages test

* test(e2e): drop the harness unit test, the split stack run proves the routing live

---------

Co-authored-by: mateo-berri <277851410+mateo-berri@users.noreply.github.com>

tests/e2e/llm_translation/test_credential_messages_e2e.py

@@ -49,5 +49,6 @@ class TestCredentialBackedMessages:
             extra_body=NO_PROXY_CACHE,
         )
         assert message.role == "assistant", f"unexpected role: {message.role!r}"
+        assert message.usage.output_tokens > 0, f"/v1/messages billed no output tokens: {message.usage!r}"
         text = "".join(block.text for block in message.content if block.type == "text")
         assert text.strip(), f"/v1/messages returned no text: {message.content!r}"

tests/e2e/transport.py

@@ -312,8 +312,10 @@ CONTROL_PLANE_PREFIXES: tuple[str, ...] = (
     "/global",
     "/config",
     "/guardrails",
+    "/credentials",
     "/router/settings",
     "/audit",
+    "/public",
     "/v2/login",
     "/openapi.json",
 )