fix: harden A2A provider routing

litellm/a2a_protocol/litellm_completion_bridge/handler.py

@@ -174,6 +174,12 @@ class A2ACompletionBridgeHandler:
                 verbose_logger.info("A2A: Using provider config for %s", custom_llm_provider)
 
                 provider_params: Final = dict(params)
+                if custom_llm_provider == "pydantic_ai_agents" or (
+                    custom_llm_provider == "bedrock"
+                    and isinstance(litellm_params.get("model"), str)
+                    and "agentcore" in litellm_params["model"]
+                ):
+                    provider_params.pop("messages", None)
                 provider_kwargs: Final[dict[str, Any]] = {
                     "request_id": request_id,
                     "params": provider_params,
@@ -250,6 +256,12 @@ class A2ACompletionBridgeHandler:
                 verbose_logger.info("A2A: Using provider config for %s (streaming)", custom_llm_provider)
 
                 provider_params: Final = dict(params)
+                if custom_llm_provider == "pydantic_ai_agents" or (
+                    custom_llm_provider == "bedrock"
+                    and isinstance(litellm_params.get("model"), str)
+                    and "agentcore" in litellm_params["model"]
+                ):
+                    provider_params.pop("messages", None)
                 provider_kwargs: Final[dict[str, Any]] = {
                     "request_id": request_id,
                     "params": provider_params,
@@ -429,7 +441,7 @@ class A2ACompletionBridgeHandler:
                     "message": {
                         "kind": "message",
                         "role": "agent",
-                        "parts": [{"kind": "text", "text": choice_texts[choice_index]}],
+                        "parts": [{"kind": "text", "text": ""}],
                         **(
                             {"tool_calls": choice_tool_calls[choice_index]}
                             if choice_tool_calls.get(choice_index)

litellm/proxy/agent_endpoints/a2a_routing.py

@@ -147,7 +147,16 @@ async def _route_registered_provider(
         **_OBJECT_DICT_ADAPTER.validate_python(litellm_params),
         **{key: data[key] for key in _FORWARDED_REQUEST_PARAMS if key in data and data[key] is not None},
     }
-    bridge_params: Final = _OBJECT_DICT_ADAPTER.validate_python(params)
+    registered_provider: Final = litellm_params.get("custom_llm_provider")
+    registered_model: Final = litellm_params.get("model")
+    native_provider: Final = registered_provider == "pydantic_ai_agents" or (
+        registered_provider == "bedrock"
+        and isinstance(registered_model, str)
+        and "agentcore" in registered_model
+    )
+    bridge_params: Final = _OBJECT_DICT_ADAPTER.validate_python(
+        {"message": params["message"]} if native_provider else params
+    )
     configured_headers: Final = litellm_params.get("extra_headers") or litellm_params.get("headers")
     configured_headers_dict: Final = (
         _HEADERS_ADAPTER.validate_python(configured_headers) if isinstance(configured_headers, dict) else None
@@ -550,10 +559,7 @@ async def route_a2a_agent_request(
     )
     configured_api_base: Final = registered_params_value.get("api_base") if registered_params_value else None
     api_base: Final = configured_api_base if isinstance(configured_api_base, str) and configured_api_base else agent_url
-    registered_model: Final = registered_params_value.get("model") if registered_params_value else None
-    cardless_provider: Final = registered_provider == "watsonx_orchestrate" or (
-        registered_provider == "bedrock" and isinstance(registered_model, str) and "agentcore" in registered_model
-    )
+    cardless_provider: Final = registered_provider is not None and registered_provider != "a2a"
     has_configured_api_base: Final = isinstance(configured_api_base, str) and bool(configured_api_base)
     if (not isinstance(agent_url, str) or not agent_url) and not has_configured_api_base and not cardless_provider:
         verbose_proxy_logger.error("[A2A] Agent '%s' has no URL configured", agent_name)

tests/test_litellm/a2a_protocol/test_completion_bridge_streaming.py

@@ -352,8 +352,7 @@ async def test_handle_streaming_preserves_multiple_choices():
 
     choices = events[-1]["result"]["choices"]
     assert [choice["index"] for choice in choices] == [0, 1]
-    assert choices[0]["message"]["parts"][0]["text"] == "first"
-    assert choices[1]["message"]["parts"][0]["text"] == "second"
+    assert [choice["message"]["parts"][0]["text"] for choice in choices] == ["", ""]
     assert choices[1]["finish_reason"] == "length"
 
 
@@ -433,6 +432,34 @@ async def test_provider_config_receives_full_message_history():
     assert provider_config.handle_non_streaming.await_args.kwargs["params"]["messages"] == messages
 
 
+@pytest.mark.asyncio
+async def test_native_provider_config_drops_internal_message_history():
+    from litellm.a2a_protocol.litellm_completion_bridge.handler import (
+        A2ACompletionBridgeHandler,
+    )
+
+    provider_config = MagicMock()
+    provider_config.handle_non_streaming = AsyncMock(return_value={"result": {}})
+    params = {
+        "message": {"role": "user", "parts": []},
+        "messages": [{"role": "user", "content": "Hello"}],
+    }
+
+    with patch(
+        "litellm.a2a_protocol.litellm_completion_bridge.handler.A2AProviderConfigManager.get_provider_config",
+        return_value=provider_config,
+    ):
+        await A2ACompletionBridgeHandler.handle_non_streaming(
+            request_id="req-native",
+            params=params,
+            litellm_params={"custom_llm_provider": "pydantic_ai_agents", "model": "agent"},
+        )
+
+    assert provider_config.handle_non_streaming.await_args.kwargs["params"] == {
+        "message": params["message"]
+    }
+
+
 def test_response_transform_preserves_audio_and_logprobs():
     from litellm.a2a_protocol.litellm_completion_bridge.transformation import (
         A2ACompletionBridgeTransformation,