feat(adk): Add support for nested subagents tool calls

py/src/braintrust/integrations/adk/cassettes/test_adk_nested_subagent_tool_calls_are_traced.yaml

@@ -0,0 +1,137 @@
+interactions:
+- request:
+    body: '{"contents": [{"parts": [{"text": "What''s the weather in San Francisco?"}],
+      "role": "user"}], "systemInstruction": {"parts": [{"text": "You are a helpful
+      weather assistant. Use the get_weather tool to answer questions about weather.\n\nYou
+      are an agent. Your internal name is \"weather_agent\"."}], "role": "user"},
+      "tools": [{"functionDeclarations": [{"description": "Get the weather for a location.",
+      "name": "get_weather", "parameters": {"properties": {"location": {"type": "STRING"}},
+      "required": ["location"], "type": "OBJECT"}}]}], "generationConfig": {}}'
+    headers:
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+      - gzip, deflate
+      connection:
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+      - application/json
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+      - generativelanguage.googleapis.com
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+      - Thu, 18 Sep 2025 20:09:51 GMT
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+      X-Frame-Options:
+      - SAMEORIGIN
+      X-XSS-Protection:
+      - '0'
+    status:
+      code: 200
+      message: OK
+- request:
+    body: '{"contents": [{"parts": [{"text": "What''s the weather in San Francisco?"}],
+      "role": "user"}, {"parts": [{"functionCall": {"args": {"location": "San Francisco"},
+      "name": "get_weather"}}], "role": "model"}, {"parts": [{"functionResponse":
+      {"name": "get_weather", "response": {"location": "San Francisco", "temperature":
+      "72\u00b0F", "condition": "sunny", "humidity": "45%", "wind": "5 mph NW"}}}],
+      "role": "user"}], "systemInstruction": {"parts": [{"text": "You are a helpful
+      weather assistant. Use the get_weather tool to answer questions about weather.\n\nYou
+      are an agent. Your internal name is \"weather_agent\"."}], "role": "user"},
+      "tools": [{"functionDeclarations": [{"description": "Get the weather for a location.",
+      "name": "get_weather", "parameters": {"properties": {"location": {"type": "STRING"}},
+      "required": ["location"], "type": "OBJECT"}}]}], "generationConfig": {}}'
+    headers:
+      accept:
+      - '*/*'
+      accept-encoding:
+      - gzip, deflate
+      connection:
+      - keep-alive
+      content-length:
+      - '881'
+      content-type:
+      - application/json
+      host:
+      - generativelanguage.googleapis.com
+      user-agent:
+      - google-genai-sdk/1.31.0 gl-python/3.9.21 google-adk/1.14.1 gl-python/3.9.21
+      x-goog-api-client:
+      - google-genai-sdk/1.31.0 gl-python/3.9.21 google-adk/1.14.1 gl-python/3.9.21
+    method: POST
+    uri: https://generativelanguage.googleapis.com/v1beta/models/gemini-2.0-flash:generateContent
+  response:
+    body:
+      string: !!binary |
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+        AA==
+    headers:
+      Alt-Svc:
+      - h3=":443"; ma=2592000,h3-29=":443"; ma=2592000
+      Content-Encoding:
+      - gzip
+      Content-Type:
+      - application/json; charset=UTF-8
+      Date:
+      - Thu, 18 Sep 2025 20:09:52 GMT
+      Server:
+      - scaffolding on HTTPServer2
+      Server-Timing:
+      - gfet4t7; dur=612
+      Transfer-Encoding:
+      - chunked
+      Vary:
+      - Origin
+      - X-Origin
+      - Referer
+      X-Content-Type-Options:
+      - nosniff
+      X-Frame-Options:
+      - SAMEORIGIN
+      X-XSS-Protection:
+      - '0'
+    status:
+      code: 200
+      message: OK
+version: 1

py/src/braintrust/integrations/adk/integration.py

@@ -10,6 +10,7 @@
     McpToolPatcher,
     RunnerRunSyncPatcher,
     ThreadBridgePatcher,
+    ToolCallAsyncPatcher,
 )
 
 
@@ -27,5 +28,6 @@ class ADKIntegration(BaseIntegration):
         AgentRunAsyncPatcher,
         RunnerRunSyncPatcher,
         FlowRunAsyncPatcher,
+        ToolCallAsyncPatcher,
         McpToolPatcher,
     )

py/src/braintrust/integrations/adk/patchers.py

@@ -12,6 +12,7 @@
     _mcp_tool_run_async_wrapper_async,
     _runner_run_async_wrapper,
     _runner_run_wrapper,
+    _tool_call_async_wrapper,
 )
 
 
@@ -89,6 +90,20 @@ class FlowRunAsyncPatcher(CompositeFunctionWrapperPatcher):
     sub_patchers = (_FlowRunAsyncSubPatcher, _FlowCallLlmAsyncSubPatcher)
 
 
+# ---------------------------------------------------------------------------
+# Tool patcher
+# ---------------------------------------------------------------------------
+
+
+class ToolCallAsyncPatcher(FunctionWrapperPatcher):
+    """Patch ADK's central async tool execution helper for tracing."""
+
+    name = "adk.tool.call_async"
+    target_module = "google.adk.flows.llm_flows.functions"
+    target_path = "__call_tool_async"
+    wrapper = _tool_call_async_wrapper
+
+
 # ---------------------------------------------------------------------------
 # Thread-bridge patchers
 # ---------------------------------------------------------------------------

py/src/braintrust/integrations/adk/test_adk.py

@@ -13,7 +13,7 @@
 
 
 ADK_VERSION = tuple(int(x) for x in pkg_version("google-adk").split(".")[:3])
-from google.adk.agents import LlmAgent
+from google.adk.agents import LlmAgent, ParallelAgent, SequentialAgent
 from google.adk.runners import Runner
 from google.adk.sessions import InMemorySessionService
 from google.genai import types
@@ -226,6 +226,69 @@ def get_weather(location: str):
     assert "72" in response_output, "Response doesn't mention temperature"
 
 
+@pytest.mark.vcr
+@pytest.mark.asyncio
+async def test_adk_nested_subagent_tool_calls_are_traced(memory_logger):
+    assert not memory_logger.pop()
+
+    def get_weather(location: str):
+        """Get the weather for a location."""
+        return {
+            "location": location,
+            "temperature": "72°F",
+            "condition": "sunny",
+        }
+
+    leaf_agent = Agent(
+        name="weather_agent",
+        model="gemini-2.0-flash",
+        instruction="You are a helpful weather assistant. Use the get_weather tool to answer questions about weather.",
+        tools=[get_weather],
+    )
+    agent = SequentialAgent(
+        name="root_agent",
+        sub_agents=[
+            ParallelAgent(
+                name="parallel_weather_agent",
+                sub_agents=[leaf_agent],
+            )
+        ],
+    )
+
+    app_name = "nested_weather_app"
+    user_id = "test-user"
+    session_id = "test-session-nested"
+
+    session_service = InMemorySessionService()
+    await session_service.create_session(app_name=app_name, user_id=user_id, session_id=session_id)
+
+    runner = Runner(agent=agent, app_name=app_name, session_service=session_service)
+    user_msg = types.Content(role="user", parts=[types.Part(text="What's the weather in San Francisco?")])
+
+    responses = []
+    async for event in runner.run_async(user_id=user_id, session_id=session_id, new_message=user_msg):
+        if event.is_final_response():
+            responses.append(event)
+
+    assert responses
+    assert responses[0].content
+    response_text = responses[0].content.parts[0].text
+    assert "san francisco" in response_text.lower()
+
+    spans = memory_logger.pop()
+
+    tool_spans = [row for row in spans if row["span_attributes"]["type"] == "tool"]
+    assert len(tool_spans) == 1, (
+        f"Expected one tool span, got {[row['span_attributes']['name'] for row in tool_spans]}"
+    )
+
+    tool_span = tool_spans[0]
+    assert tool_span["span_attributes"]["name"] == "tool [get_weather]"
+    assert tool_span["input"]["arguments"] == {"location": "San Francisco"}
+    assert tool_span["output"]["location"] == "San Francisco"
+    assert tool_span["output"]["temperature"] == "72°F"
+
+
 @pytest.mark.vcr
 @pytest.mark.asyncio
 async def test_adk_max_tokens_captures_content(memory_logger):

py/src/braintrust/integrations/adk/tracing.py

@@ -548,6 +548,31 @@ async def _trace():
             yield event
 
 
+async def _tool_call_async_wrapper(wrapped: Any, instance: Any, args: Any, kwargs: Any):
+    tool = args[0] if len(args) > 0 else kwargs.get("tool")
+    tool_args = args[1] if len(args) > 1 else kwargs.get("args", {})
+
+    # MCP tools already have a dedicated wrapper. Skip here to avoid duplicate tool spans.
+    if tool is not None and getattr(tool.__class__, "__module__", "").startswith("google.adk.tools.mcp_tool"):
+        return await wrapped(*args, **kwargs)
+
+    tool_name = getattr(tool, "name", tool.__class__.__name__ if tool is not None else "unknown")
+
+    with start_span(
+        name=f"tool [{tool_name}]",
+        type=SpanTypeAttribute.TOOL,
+        input={"tool_name": tool_name, "arguments": bt_safe_deep_copy(tool_args)},
+        metadata={"tool_class": tool.__class__.__name__ if tool is not None else None},
+    ) as tool_span:
+        try:
+            result = await wrapped(*args, **kwargs)
+            tool_span.log(output=result)
+            return result
+        except Exception as e:
+            tool_span.log(error=str(e))
+            raise
+
+
 async def _mcp_tool_run_async_wrapper_async(wrapped: Any, instance: Any, args: Any, kwargs: Any):
     # Extract tool information
     tool_name = instance.name