refactor: migrate auxiliary_client Anthropic path to use transport

Replace direct normalize_anthropic_response() call in
_AnthropicCompletionsAdapter.create() with
AnthropicTransport.normalize_response() via get_transport().

Before: auxiliary_client called adapter v1 directly, bypassing
the transport layer entirely.

After: auxiliary_client → get_transport('anthropic_messages') →
transport.normalize_response() → adapter v1 → NormalizedResponse.

The adapter v1 function (normalize_anthropic_response) now has
zero callers outside agent/anthropic_adapter.py and the transport.
This unblocks collapsing v1 to return NormalizedResponse directly
in a follow-up (the remaining 2-layer chain becomes 1-layer).

WS1 item 2 of Cycle 2 (#14418).

agent/auxiliary_client.py

@@ -573,7 +573,8 @@ class _AnthropicCompletionsAdapter:
         self._is_oauth = is_oauth
 
     def create(self, **kwargs) -> Any:
-        from agent.anthropic_adapter import build_anthropic_kwargs, normalize_anthropic_response
+        from agent.anthropic_adapter import build_anthropic_kwargs
+        from agent.transports import get_transport
 
         messages = kwargs.get("messages", [])
         model = kwargs.get("model", self._model)
@@ -610,7 +611,28 @@ class _AnthropicCompletionsAdapter:
                 anthropic_kwargs["temperature"] = temperature
 
         response = self._client.messages.create(**anthropic_kwargs)
-        assistant_message, finish_reason = normalize_anthropic_response(response)
+        _transport = get_transport("anthropic_messages")
+        _nr = _transport.normalize_response(
+            response, strip_tool_prefix=self._is_oauth
+        )
+
+        # Map NormalizedResponse → OpenAI-compatible SimpleNamespace
+        tool_calls = None
+        if _nr.tool_calls:
+            tool_calls = [
+                SimpleNamespace(
+                    id=tc.id,
+                    type="function",
+                    function=SimpleNamespace(name=tc.name, arguments=tc.arguments),
+                )
+                for tc in _nr.tool_calls
+            ]
+        assistant_message = SimpleNamespace(
+            content=_nr.content,
+            tool_calls=tool_calls,
+            reasoning=_nr.reasoning,
+        )
+        finish_reason = _nr.finish_reason
 
         usage = None
         if hasattr(response, "usage") and response.usage: