fix(telemetry): Port inline binary data summarization on spans to v1

Serializing a content part in JSON mode base64-encodes its inline_data, so the
model response span and the trace_send_data span carried the bytes themselves.
A live session's audio chunks and any image or document a user uploaded were
copied wholesale onto an exported span attribute, which sent the payload to the
trace backend and grew the span with it.

Now a new private helper replaces every part that has inline_data with a text
part reading "<inline_data: {mime}, {n} bytes>", and both call sites route
their content through it. The request side already dropped inline parts and is
unchanged.

Behaviour change: anyone who was reading audio or image bytes back out of a
span now gets that description string instead. The model still receives the
real bytes; only the span is summarized.

src/google/adk/telemetry/tracing.py

@@ -360,7 +360,12 @@ def trace_call_llm(
 
   if _should_add_request_response_to_spans():
     try:
-      llm_response_json = llm_response.model_dump_json(exclude_none=True)
+      response_for_trace = llm_response
+      if llm_response.content is not None:
+        response_for_trace = llm_response.model_copy(
+            update={'content': _summarize_inline_data(llm_response.content)}
+        )
+      llm_response_json = response_for_trace.model_dump_json(exclude_none=True)
     except Exception:  # pylint: disable=broad-exception-caught
       llm_response_json = '<not serializable>'
 
@@ -409,6 +414,37 @@ def trace_call_llm(
     )
 
 
+def _summarize_inline_data(content: types.Content) -> types.Content:
+  """Returns ``content`` with inline binary parts reduced to a description.
+
+  Serializing a part in JSON mode base64-encodes its ``inline_data``, so a
+  live session's audio chunks would otherwise be copied wholesale onto a span
+  attribute. Only the mime type and byte count are kept.
+
+  Args:
+    content: The content to summarize.
+
+  Returns:
+    A copy of ``content`` whose inline binary parts carry a text description
+    instead of the bytes.
+  """
+  parts: list[types.Part] = []
+  for part in content.parts or []:
+    blob = part.inline_data
+    if blob is None:
+      parts.append(part)
+      continue
+    parts.append(
+        types.Part(
+            text=(
+                f"<inline_data: {blob.mime_type or 'unknown'},"
+                f" {len(blob.data or b'')} bytes>"
+            )
+        )
+    )
+  return types.Content(role=content.role, parts=parts)
+
+
 def trace_send_data(
     invocation_context: InvocationContext,
     event_id: str,
@@ -435,7 +471,7 @@ def trace_send_data(
     span.set_attribute(
         'gcp.vertex.agent.data',
         _safe_json_serialize([
-            types.Content(role=content.role, parts=content.parts).model_dump(
+            _summarize_inline_data(content).model_dump(
                 exclude_none=True, mode='json'
             )
             for content in data

tests/unittests/telemetry/test_spans.py

@@ -802,6 +802,123 @@ async def test_trace_send_data_disabling_request_response_content(
   )
 
 
+@pytest.mark.asyncio
+async def test_trace_call_llm_summarizes_response_inline_data(
+    monkeypatch, mock_span_fixture
+):
+  """Inline binary data in the response is described, not copied to the span."""
+  monkeypatch.setattr(
+      'opentelemetry.trace.get_current_span', lambda: mock_span_fixture
+  )
+
+  agent = LlmAgent(name='test_agent')
+  invocation_context = await _create_invocation_context(agent)
+  llm_request = LlmRequest(
+      model='gemini-pro', config=types.GenerateContentConfig()
+  )
+  llm_response = LlmResponse(
+      content=types.Content(
+          role='model',
+          parts=[
+              types.Part(text='hi'),
+              types.Part.from_bytes(data=b'test_data', mime_type='audio/pcm'),
+          ],
+      )
+  )
+
+  trace_call_llm(invocation_context, 'test_event_id', llm_request, llm_response)
+
+  llm_response_json = next(
+      call_obj.args[1]
+      for call_obj in mock_span_fixture.set_attribute.call_args_list
+      if call_obj.args[0] == 'gcp.vertex.agent.llm_response'
+  )
+
+  # b'test_data' base64-encodes to 'dGVzdF9kYXRh'.
+  assert 'dGVzdF9kYXRh' not in llm_response_json
+  assert 'hi' in llm_response_json
+  assert '<inline_data: audio/pcm, 9 bytes>' in llm_response_json
+
+
+@pytest.mark.asyncio
+async def test_trace_send_data_summarizes_inline_data(
+    monkeypatch, mock_span_fixture
+):
+  """Inline binary data is described on the span, never copied onto it."""
+  monkeypatch.setenv(ADK_CAPTURE_MESSAGE_CONTENT_IN_SPANS, 'true')
+  monkeypatch.setattr(
+      'opentelemetry.trace.get_current_span', lambda: mock_span_fixture
+  )
+
+  agent = LlmAgent(name='test_agent')
+  invocation_context = await _create_invocation_context(agent)
+
+  trace_send_data(
+      invocation_context=invocation_context,
+      event_id='test_event_id',
+      data=[
+          types.Content(
+              role='user',
+              parts=[
+                  types.Part(text='hi'),
+                  types.Part.from_bytes(
+                      data=b'test_data', mime_type='audio/pcm'
+                  ),
+              ],
+          )
+      ],
+  )
+
+  data_json = next(
+      call_obj.args[1]
+      for call_obj in mock_span_fixture.set_attribute.call_args_list
+      if call_obj.args[0] == 'gcp.vertex.agent.data'
+  )
+
+  # b'test_data' base64-encodes to 'dGVzdF9kYXRh'.
+  assert 'dGVzdF9kYXRh' not in data_json
+  assert 'hi' in data_json
+  assert '<inline_data: audio/pcm, 9 bytes>' in data_json
+
+
+@pytest.mark.asyncio
+async def test_trace_send_data_summarizes_blob_without_mime_type(
+    monkeypatch, mock_span_fixture
+):
+  """A blob is described even when its mime type and bytes are unset.
+
+  The parts-less content in the same call pins that summarizing tolerates
+  ``Content.parts`` being unset.
+  """
+  monkeypatch.setenv(ADK_CAPTURE_MESSAGE_CONTENT_IN_SPANS, 'true')
+  monkeypatch.setattr(
+      'opentelemetry.trace.get_current_span', lambda: mock_span_fixture
+  )
+
+  agent = LlmAgent(name='test_agent')
+  invocation_context = await _create_invocation_context(agent)
+
+  trace_send_data(
+      invocation_context=invocation_context,
+      event_id='test_event_id',
+      data=[
+          types.Content(role='user'),
+          types.Content(
+              role='user', parts=[types.Part(inline_data=types.Blob())]
+          ),
+      ],
+  )
+
+  data_json = next(
+      call_obj.args[1]
+      for call_obj in mock_span_fixture.set_attribute.call_args_list
+      if call_obj.args[0] == 'gcp.vertex.agent.data'
+  )
+
+  assert '<inline_data: unknown, 0 bytes>' in data_json
+  assert 'inlineData' not in data_json
+
+
 @pytest.mark.asyncio
 @mock.patch('google.adk.telemetry.tracing.otel_logger')
 @mock.patch('google.adk.telemetry.tracing.tracer')