fix: Fixes thought handling in contents.py and refactors its unit tests

Before this change, other agent's reply with thought will still be inserted in the outgoing LlmRequest due to the wrong `else` statement for calling all other type of part.

This commit also refactors test_contents.py to be behavior-oriented tests, instead of implementation-oriented, and add more test cases to cover expected scenarios.

The tests are divided into the following files with different focus:

- test_contents.py: covers the basic logic of event filter;
- test_contents_branch.py: covers the behavior related to branch, which takes effect when ParallelAgent is used.
- test_contents_other_agent.py: covers the retelling behavior to include other agents' reply as context for the current agent.
- test_contents_function.py: covers the function_call/function_response rearrangement logic mainly for `LongRunningFunctionTool`.

PiperOrigin-RevId: 802759821

src/google/adk/agents/remote_a2a_agent.py

@@ -63,8 +63,8 @@ from ..a2a.logs.log_utils import build_a2a_request_log
 from ..a2a.logs.log_utils import build_a2a_response_log
 from ..agents.invocation_context import InvocationContext
 from ..events.event import Event
-from ..flows.llm_flows.contents import _convert_foreign_event
 from ..flows.llm_flows.contents import _is_other_agent_reply
+from ..flows.llm_flows.contents import _present_other_agent_message
 from ..flows.llm_flows.functions import find_matching_function_call
 from .base_agent import BaseAgent
 
@@ -338,7 +338,7 @@ class RemoteA2aAgent(BaseAgent):
     context_id = None
     for event in reversed(ctx.session.events):
       if _is_other_agent_reply(self.name, event):
-        event = _convert_foreign_event(event)
+        event = _present_other_agent_message(event)
       elif event.author == self.name:
         # stop on content generated by current a2a agent given it should already
         # be in remote session

src/google/adk/flows/llm_flows/contents.py

@@ -16,7 +16,6 @@ from __future__ import annotations
 
 import copy
 from typing import AsyncGenerator
-from typing import Generator
 from typing import Optional
 
 from google.genai import types
@@ -203,6 +202,25 @@ def _rearrange_events_for_latest_function_response(
   return result_events
 
 
+def _contains_empty_content(event: Event) -> bool:
+  """Check if an event should be skipped due to missing or empty content.
+
+  This can happen to the evnets that only changed session state.
+
+  Args:
+    event: The event to check.
+
+  Returns:
+    True if the event should be skipped, False otherwise.
+  """
+  return (
+      not event.content
+      or not event.content.role
+      or not event.content.parts
+      or event.content.parts[0].text == ''
+  )
+
+
 def _get_contents(
     current_branch: Optional[str], events: list[Event], agent_name: str = ''
 ) -> list[types.Content]:
@@ -222,16 +240,7 @@ def _get_contents(
   # Parse the events, leaving the contents and the function calls and
   # responses from the current agent.
   for event in events:
-    if (
-        not event.content
-        or not event.content.role
-        or not event.content.parts
-        or event.content.parts[0].text == ''
-    ):
-      # Skip events without content, or generated neither by user nor by model
-      # or has empty text.
-      # E.g. events purely for mutating session states.
-
+    if _contains_empty_content(event):
       continue
     if not _is_event_belongs_to_branch(current_branch, event):
       # Skip events not belong to current branch.
@@ -242,11 +251,12 @@ def _get_contents(
     if _is_request_confirmation_event(event):
       # Skip request confirmation events.
       continue
-    filtered_events.append(
-        _convert_foreign_event(event)
-        if _is_other_agent_reply(agent_name, event)
-        else event
-    )
+
+    if _is_other_agent_reply(agent_name, event):
+      if converted_event := _present_other_agent_message(event):
+        filtered_events.append(converted_event)
+    else:
+      filtered_events.append(event)
 
   # Rearrange events for proper function call/response pairing
   result_events = _rearrange_events_for_latest_function_response(
@@ -305,19 +315,18 @@ def _is_other_agent_reply(current_agent_name: str, event: Event) -> bool:
   )
 
 
-def _convert_foreign_event(event: Event) -> Event:
-  """Converts an event authored by another agent as a user-content event.
+def _present_other_agent_message(event: Event) -> Optional[Event]:
+  """Presents another agent's message as user context for the current agent.
 
-  This is to provide another agent's output as context to the current agent, so
-  that current agent can continue to respond, such as summarizing previous
-  agent's reply, etc.
+  Reformats the event with role='user' and adds '[agent_name] said:' prefix
+  to provide context without confusion about authorship.
 
   Args:
-    event: The event to convert.
+    event: The event from another agent to present as context.
 
   Returns:
-    The converted event.
-
+    Event reformatted as user-role context with agent attribution, or None
+    if no meaningful content remains after filtering.
   """
   if not event.content or not event.content.parts:
     return event
@@ -326,8 +335,10 @@ def _convert_foreign_event(event: Event) -> Event:
   content.role = 'user'
   content.parts = [types.Part(text='For context:')]
   for part in event.content.parts:
-    # Exclude thoughts from the context.
-    if part.text and not part.thought:
+    if part.thought:
+      # Exclude thoughts from the context.
+      continue
+    elif part.text:
       content.parts.append(
           types.Part(text=f'[{event.author}] said: {part.text}')
       )
@@ -354,6 +365,10 @@ def _convert_foreign_event(event: Event) -> Event:
     else:
       content.parts.append(part)
 
+  # If no meaningful parts were added (only "For context:" remains), return None
+  if len(content.parts) == 1:
+    return None
+
   return Event(
       timestamp=event.timestamp,
       author='user',
@@ -429,7 +444,11 @@ def _merge_function_response_events(
 def _is_event_belongs_to_branch(
     invocation_branch: Optional[str], event: Event
 ) -> bool:
-  """Event belongs to a branch, when event.branch is prefix of the invocation branch."""
+  """Check if an event belongs to the current branch.
+
+  This is for event context segration between agents. E.g. agent A shouldn't
+  see output of agent B.
+  """
   if not invocation_branch or not event.branch:
     return True
   return invocation_branch.startswith(event.branch)

src/google/adk/flows/llm_flows/functions.py

@@ -65,7 +65,15 @@ def populate_client_function_call_id(model_response_event: Event) -> None:
       function_call.id = generate_client_function_call_id()
 
 
-def remove_client_function_call_id(content: types.Content) -> None:
+def remove_client_function_call_id(content: Optional[types.Content]) -> None:
+  """Removes ADK-generated function call IDs from content before sending to LLM.
+
+  Strips client-side function call/response IDs that start with 'adk-' prefix
+  to avoid sending internal tracking IDs to the model.
+
+  Args:
+    content: Content containing function calls/responses to clean.
+  """
   if content and content.parts:
     for part in content.parts:
       if (

tests/unittests/agents/test_remote_a2a_agent.py

@@ -515,7 +515,7 @@ class TestRemoteA2aAgentMessageHandling:
     self.mock_session.events = [mock_event]
 
     with patch(
-        "google.adk.agents.remote_a2a_agent._convert_foreign_event"
+        "google.adk.agents.remote_a2a_agent._present_other_agent_message"
     ) as mock_convert:
       mock_convert.return_value = mock_event
 
@@ -937,7 +937,7 @@ class TestRemoteA2aAgentIntegration:
 
     # Mock dependencies
     with patch(
-        "google.adk.agents.remote_a2a_agent._convert_foreign_event"
+        "google.adk.agents.remote_a2a_agent._present_other_agent_message"
     ) as mock_convert:
       mock_convert.return_value = mock_event
 

tests/unittests/flows/llm_flows/test_contents_branch.py

@@ -0,0 +1,288 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Tests for branch filtering in contents module.
+
+Branch format: agent_1.agent_2.agent_3 (parent.child.grandchild)
+Child agents can see parent agents' events, but not sibling agents' events.
+"""
+
+from google.adk.agents.llm_agent import Agent
+from google.adk.events.event import Event
+from google.adk.flows.llm_flows.contents import request_processor
+from google.adk.models.llm_request import LlmRequest
+from google.genai import types
+import pytest
+
+from ... import testing_utils
+
+
+@pytest.mark.asyncio
+async def test_branch_filtering_child_sees_parent():
+  """Test that child agents can see parent agents' events."""
+  agent = Agent(model="gemini-2.5-flash", name="child_agent")
+  llm_request = LlmRequest(model="gemini-2.5-flash")
+  invocation_context = await testing_utils.create_invocation_context(
+      agent=agent
+  )
+  # Set current branch as child of "parent_agent"
+  invocation_context.branch = "parent_agent.child_agent"
+
+  # Add events from parent and child levels
+  events = [
+      Event(
+          invocation_id="inv1",
+          author="user",
+          content=types.UserContent("User message"),
+      ),
+      Event(
+          invocation_id="inv2",
+          author="parent_agent",
+          content=types.ModelContent("Parent agent response"),
+          branch="parent_agent",  # Parent branch - should be included
+      ),
+      Event(
+          invocation_id="inv3",
+          author="child_agent",
+          content=types.ModelContent("Child agent response"),
+          branch="parent_agent.child_agent",  # Current branch - should be included
+      ),
+  ]
+  invocation_context.session.events = events
+
+  # Process the request
+  async for _ in request_processor.run_async(invocation_context, llm_request):
+    pass
+
+  # Verify child can see user message and parent events, but not sibling events
+  assert len(llm_request.contents) == 3
+  assert llm_request.contents[0] == types.UserContent("User message")
+  assert llm_request.contents[1].role == "user"
+  assert llm_request.contents[1].parts == [
+      types.Part(text="For context:"),
+      types.Part(text="[parent_agent] said: Parent agent response"),
+  ]
+  assert llm_request.contents[2] == types.ModelContent("Child agent response")
+
+
+@pytest.mark.asyncio
+async def test_branch_filtering_excludes_sibling_agents():
+  """Test that sibling agents cannot see each other's events."""
+  agent = Agent(model="gemini-2.5-flash", name="child_agent1")
+  llm_request = LlmRequest(model="gemini-2.5-flash")
+  invocation_context = await testing_utils.create_invocation_context(
+      agent=agent
+  )
+  # Set current branch as first child
+  invocation_context.branch = "parent_agent.child_agent1"
+
+  # Add events from parent, current child, and sibling child
+  events = [
+      Event(
+          invocation_id="inv1",
+          author="user",
+          content=types.UserContent("User message"),
+      ),
+      Event(
+          invocation_id="inv2",
+          author="parent_agent",
+          content=types.ModelContent("Parent response"),
+          branch="parent_agent",  # Parent - should be included
+      ),
+      Event(
+          invocation_id="inv3",
+          author="child_agent1",
+          content=types.ModelContent("Child1 response"),
+          branch="parent_agent.child_agent1",  # Current - should be included
+      ),
+      Event(
+          invocation_id="inv4",
+          author="child_agent2",
+          content=types.ModelContent("Sibling response"),
+          branch="parent_agent.child_agent2",  # Sibling - should be excluded
+      ),
+  ]
+  invocation_context.session.events = events
+
+  # Process the request
+  async for _ in request_processor.run_async(invocation_context, llm_request):
+    pass
+
+  # Verify sibling events are excluded, but parent and current agent events included
+  assert len(llm_request.contents) == 3
+  assert llm_request.contents[0] == types.UserContent("User message")
+  assert llm_request.contents[1].role == "user"
+  assert llm_request.contents[1].parts == [
+      types.Part(text="For context:"),
+      types.Part(text="[parent_agent] said: Parent response"),
+  ]
+  assert llm_request.contents[2] == types.ModelContent("Child1 response")
+
+
+@pytest.mark.asyncio
+async def test_branch_filtering_no_branch_allows_all():
+  """Test that events are included when no branches are set."""
+  agent = Agent(model="gemini-2.5-flash", name="current_agent")
+  llm_request = LlmRequest(model="gemini-2.5-flash")
+  invocation_context = await testing_utils.create_invocation_context(
+      agent=agent
+  )
+  # No current branch set (None)
+  invocation_context.branch = None
+
+  # Add events with and without branches
+  events = [
+      Event(
+          invocation_id="inv1",
+          author="user",
+          content=types.UserContent("No branch message"),
+          branch=None,
+      ),
+      Event(
+          invocation_id="inv2",
+          author="agent1",
+          content=types.ModelContent("Agent with branch"),
+          branch="agent1",
+      ),
+      Event(
+          invocation_id="inv3",
+          author="user",
+          content=types.UserContent("Another no branch"),
+          branch=None,
+      ),
+  ]
+  invocation_context.session.events = events
+
+  # Process the request
+  async for _ in request_processor.run_async(invocation_context, llm_request):
+    pass
+
+  # Verify all events are included when no current branch
+  assert len(llm_request.contents) == 3
+  assert llm_request.contents[0] == types.UserContent("No branch message")
+  assert llm_request.contents[1].role == "user"
+  assert llm_request.contents[1].parts == [
+      types.Part(text="For context:"),
+      types.Part(text="[agent1] said: Agent with branch"),
+  ]
+  assert llm_request.contents[2] == types.UserContent("Another no branch")
+
+
+@pytest.mark.asyncio
+async def test_branch_filtering_grandchild_sees_grandparent():
+  """Test that deeply nested child agents can see all ancestor events."""
+  agent = Agent(model="gemini-2.5-flash", name="grandchild_agent")
+  llm_request = LlmRequest(model="gemini-2.5-flash")
+  invocation_context = await testing_utils.create_invocation_context(
+      agent=agent
+  )
+  # Set deeply nested branch: grandparent.parent.grandchild
+  invocation_context.branch = "grandparent_agent.parent_agent.grandchild_agent"
+
+  # Add events from all levels of hierarchy
+  events = [
+      Event(
+          invocation_id="inv1",
+          author="grandparent_agent",
+          content=types.ModelContent("Grandparent response"),
+          branch="grandparent_agent",
+      ),
+      Event(
+          invocation_id="inv2",
+          author="parent_agent",
+          content=types.ModelContent("Parent response"),
+          branch="grandparent_agent.parent_agent",
+      ),
+      Event(
+          invocation_id="inv3",
+          author="grandchild_agent",
+          content=types.ModelContent("Grandchild response"),
+          branch="grandparent_agent.parent_agent.grandchild_agent",
+      ),
+      Event(
+          invocation_id="inv4",
+          author="sibling_agent",
+          content=types.ModelContent("Sibling response"),
+          branch="grandparent_agent.parent_agent.sibling_agent",
+      ),
+  ]
+  invocation_context.session.events = events
+
+  # Process the request
+  async for _ in request_processor.run_async(invocation_context, llm_request):
+    pass
+
+  # Verify only ancestors and current level are included
+  assert len(llm_request.contents) == 3
+  assert llm_request.contents[0].role == "user"
+  assert llm_request.contents[0].parts == [
+      types.Part(text="For context:"),
+      types.Part(text="[grandparent_agent] said: Grandparent response"),
+  ]
+  assert llm_request.contents[1].role == "user"
+  assert llm_request.contents[1].parts == [
+      types.Part(text="For context:"),
+      types.Part(text="[parent_agent] said: Parent response"),
+  ]
+  assert llm_request.contents[2] == types.ModelContent("Grandchild response")
+
+
+@pytest.mark.asyncio
+async def test_branch_filtering_parent_cannot_see_child():
+  """Test that parent agents cannot see child agents' events."""
+  agent = Agent(model="gemini-2.5-flash", name="parent_agent")
+  llm_request = LlmRequest(model="gemini-2.5-flash")
+  invocation_context = await testing_utils.create_invocation_context(
+      agent=agent
+  )
+  # Set current branch as parent
+  invocation_context.branch = "parent_agent"
+
+  # Add events from parent and its children
+  events = [
+      Event(
+          invocation_id="inv1",
+          author="user",
+          content=types.UserContent("User message"),
+      ),
+      Event(
+          invocation_id="inv2",
+          author="parent_agent",
+          content=types.ModelContent("Parent response"),
+          branch="parent_agent",
+      ),
+      Event(
+          invocation_id="inv3",
+          author="child_agent",
+          content=types.ModelContent("Child response"),
+          branch="parent_agent.child_agent",
+      ),
+      Event(
+          invocation_id="inv4",
+          author="grandchild_agent",
+          content=types.ModelContent("Grandchild response"),
+          branch="parent_agent.child_agent.grandchild_agent",
+      ),
+  ]
+  invocation_context.session.events = events
+
+  # Process the request
+  async for _ in request_processor.run_async(invocation_context, llm_request):
+    pass
+
+  # Verify parent cannot see child or grandchild events
+  assert llm_request.contents == [
+      types.UserContent("User message"),
+      types.ModelContent("Parent response"),
+  ]

tests/unittests/flows/llm_flows/test_contents_other_agent.py

@@ -0,0 +1,388 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Behavioral tests for other agent message processing in contents module."""
+
+from google.adk.agents.llm_agent import Agent
+from google.adk.events.event import Event
+from google.adk.flows.llm_flows.contents import request_processor
+from google.adk.models.llm_request import LlmRequest
+from google.genai import types
+import pytest
+
+from ... import testing_utils
+
+
+@pytest.mark.asyncio
+async def test_other_agent_message_appears_as_user_context():
+  """Test that messages from other agents appear as user context."""
+  agent = Agent(model="gemini-2.5-flash", name="current_agent")
+  llm_request = LlmRequest(model="gemini-2.5-flash")
+  invocation_context = await testing_utils.create_invocation_context(
+      agent=agent
+  )
+  # Add event from another agent
+  other_agent_event = Event(
+      invocation_id="test_inv",
+      author="other_agent",
+      content=types.ModelContent("Hello from other agent"),
+  )
+  invocation_context.session.events = [other_agent_event]
+
+  # Process the request
+  async for _ in request_processor.run_async(invocation_context, llm_request):
+    pass
+
+  # Verify the other agent's message is presented as user context
+  assert llm_request.contents[0].role == "user"
+  assert llm_request.contents[0].parts == [
+      types.Part(text="For context:"),
+      types.Part(text="[other_agent] said: Hello from other agent"),
+  ]
+
+
+@pytest.mark.asyncio
+async def test_other_agent_thoughts_are_excluded():
+  """Test that thoughts from other agents are excluded from context."""
+  agent = Agent(model="gemini-2.5-flash", name="current_agent")
+  llm_request = LlmRequest(model="gemini-2.5-flash")
+  invocation_context = await testing_utils.create_invocation_context(
+      agent=agent
+  )
+  # Add event from other agent with both regular text and thoughts
+  other_agent_event = Event(
+      invocation_id="test_inv",
+      author="other_agent",
+      content=types.ModelContent([
+          types.Part(text="Public message", thought=False),
+          types.Part(text="Private thought", thought=True),
+          types.Part(text="Another public message"),
+      ]),
+  )
+  invocation_context.session.events = [other_agent_event]
+
+  # Process the request
+  async for _ in request_processor.run_async(invocation_context, llm_request):
+    pass
+
+  # Verify only non-thought parts are included (thoughts excluded)
+  assert llm_request.contents[0].role == "user"
+  assert llm_request.contents[0].parts == [
+      types.Part(text="For context:"),
+      types.Part(text="[other_agent] said: Public message"),
+      types.Part(text="[other_agent] said: Another public message"),
+  ]
+
+
+@pytest.mark.asyncio
+async def test_other_agent_function_calls():
+  """Test that function calls from other agents are preserved in context."""
+  agent = Agent(model="gemini-2.5-flash", name="current_agent")
+  llm_request = LlmRequest(model="gemini-2.5-flash")
+  invocation_context = await testing_utils.create_invocation_context(
+      agent=agent
+  )
+  # Add event from other agent with function call
+  function_call = types.FunctionCall(
+      id="func_123", name="search_tool", args={"query": "test query"}
+  )
+  other_agent_event = Event(
+      invocation_id="test_inv",
+      author="other_agent",
+      content=types.ModelContent([types.Part(function_call=function_call)]),
+  )
+  invocation_context.session.events = [other_agent_event]
+
+  # Process the request
+  async for _ in request_processor.run_async(invocation_context, llm_request):
+    pass
+
+  # Verify function call is presented as context
+  assert llm_request.contents[0].role == "user"
+  assert llm_request.contents[0].parts == [
+      types.Part(text="For context:"),
+      types.Part(
+          text="""\
+[other_agent] called tool `search_tool` with parameters: {'query': 'test query'}"""
+      ),
+  ]
+
+
+@pytest.mark.asyncio
+async def test_other_agent_function_responses():
+  """Test that function responses from other agents are properly formatted."""
+  agent = Agent(model="gemini-2.5-flash", name="current_agent")
+  llm_request = LlmRequest(model="gemini-2.5-flash")
+  invocation_context = await testing_utils.create_invocation_context(
+      agent=agent
+  )
+
+  # Add event from other agent with function response
+  function_response = types.FunctionResponse(
+      id="func_123",
+      name="search_tool",
+      response={"results": ["item1", "item2"]},
+  )
+  other_agent_event = Event(
+      invocation_id="test_inv",
+      author="other_agent",
+      content=types.Content(
+          role="user", parts=[types.Part(function_response=function_response)]
+      ),
+  )
+  invocation_context.session.events = [other_agent_event]
+
+  # Process the request
+  async for _ in request_processor.run_async(invocation_context, llm_request):
+    pass
+
+  # Verify function response is presented as context
+  assert llm_request.contents[0].role == "user"
+  assert llm_request.contents[0].parts == [
+      types.Part(text="For context:"),
+      types.Part(
+          text=(
+              "[other_agent] `search_tool` tool returned result: {'results':"
+              " ['item1', 'item2']}"
+          )
+      ),
+  ]
+
+
+@pytest.mark.asyncio
+async def test_other_agent_function_call_response():
+  """Test function call and response sequence from other agents."""
+  agent = Agent(model="gemini-2.5-flash", name="current_agent")
+  llm_request = LlmRequest(model="gemini-2.5-flash")
+  invocation_context = await testing_utils.create_invocation_context(
+      agent=agent
+  )
+  # Add function call event from other agent
+  function_call = types.FunctionCall(
+      id="func_123", name="calc_tool", args={"query": "6x7"}
+  )
+  call_event = Event(
+      invocation_id="test_inv1",
+      author="other_agent",
+      content=types.ModelContent([
+          types.Part(text="Let me calculate this"),
+          types.Part(function_call=function_call),
+      ]),
+  )
+  # Add function response event
+  function_response = types.FunctionResponse(
+      id="func_123", name="calc_tool", response={"result": 42}
+  )
+  response_event = Event(
+      invocation_id="test_inv2",
+      author="other_agent",
+      content=types.UserContent(
+          parts=[types.Part(function_response=function_response)]
+      ),
+  )
+  invocation_context.session.events = [call_event, response_event]
+
+  # Process the request
+  async for _ in request_processor.run_async(invocation_context, llm_request):
+    pass
+
+  # Verify function call and response are properly formatted
+  assert len(llm_request.contents) == 2
+
+  # Function call from other agent
+  assert llm_request.contents[0].role == "user"
+  assert llm_request.contents[0].parts == [
+      types.Part(text="For context:"),
+      types.Part(text="[other_agent] said: Let me calculate this"),
+      types.Part(
+          text=(
+              "[other_agent] called tool `calc_tool` with parameters: {'query':"
+              " '6x7'}"
+          )
+      ),
+  ]
+  # Function response from other agent
+  assert llm_request.contents[1].role == "user"
+  assert llm_request.contents[1].parts == [
+      types.Part(text="For context:"),
+      types.Part(
+          text="[other_agent] `calc_tool` tool returned result: {'result': 42}"
+      ),
+  ]
+
+
+@pytest.mark.asyncio
+async def test_other_agent_empty_content():
+  """Test that other agent messages with only thoughts or empty content are filtered out."""
+  agent = Agent(model="gemini-2.5-flash", name="current_agent")
+  llm_request = LlmRequest(model="gemini-2.5-flash")
+  invocation_context = await testing_utils.create_invocation_context(
+      agent=agent
+  )
+  # Add events: user message, other agents with empty content, user message
+  events = [
+      Event(
+          invocation_id="inv1",
+          author="user",
+          content=types.UserContent("Hello"),
+      ),
+      # Other agent with only thoughts
+      Event(
+          invocation_id="inv2",
+          author="other_agent1",
+          content=types.ModelContent([
+              types.Part(text="This is a private thought", thought=True),
+              types.Part(text="Another private thought", thought=True),
+          ]),
+      ),
+      # Other agent with empty text and thoughts
+      Event(
+          invocation_id="inv3",
+          author="other_agent2",
+          content=types.ModelContent([
+              types.Part(text="", thought=False),
+              types.Part(text="Secret thought", thought=True),
+          ]),
+      ),
+      Event(
+          invocation_id="inv4",
+          author="user",
+          content=types.UserContent("World"),
+      ),
+  ]
+  invocation_context.session.events = events
+
+  # Process the request
+  async for _ in request_processor.run_async(invocation_context, llm_request):
+    pass
+
+  # Verify empty content events are completely filtered out
+  assert llm_request.contents == [
+      types.UserContent("Hello"),
+      types.UserContent("World"),
+  ]
+
+
+@pytest.mark.asyncio
+async def test_multiple_agents_in_conversation():
+  """Test handling multiple agents in a conversation flow."""
+  agent = Agent(model="gemini-2.5-flash", name="current_agent")
+  llm_request = LlmRequest(model="gemini-2.5-flash")
+  invocation_context = await testing_utils.create_invocation_context(
+      agent=agent
+  )
+
+  # Create a multi-agent conversation
+  events = [
+      Event(
+          invocation_id="inv1",
+          author="user",
+          content=types.UserContent("Hello everyone"),
+      ),
+      Event(
+          invocation_id="inv2",
+          author="agent1",
+          content=types.ModelContent("Hi from agent1"),
+      ),
+      Event(
+          invocation_id="inv3",
+          author="agent2",
+          content=types.ModelContent("Hi from agent2"),
+      ),
+  ]
+  invocation_context.session.events = events
+
+  # Process the request
+  async for _ in request_processor.run_async(invocation_context, llm_request):
+    pass
+
+  # Verify all messages are properly processed
+  assert len(llm_request.contents) == 3
+
+  # User message should remain as user
+  assert llm_request.contents[0] == types.UserContent("Hello everyone")
+  # Other agents' messages should be converted to user context
+  assert llm_request.contents[1].role == "user"
+  assert llm_request.contents[1].parts == [
+      types.Part(text="For context:"),
+      types.Part(text="[agent1] said: Hi from agent1"),
+  ]
+  assert llm_request.contents[2].role == "user"
+  assert llm_request.contents[2].parts == [
+      types.Part(text="For context:"),
+      types.Part(text="[agent2] said: Hi from agent2"),
+  ]
+
+
+@pytest.mark.asyncio
+async def test_current_agent_messages_not_converted():
+  """Test that the current agent's own messages are not converted."""
+  agent = Agent(model="gemini-2.5-flash", name="current_agent")
+  llm_request = LlmRequest(model="gemini-2.5-flash")
+  invocation_context = await testing_utils.create_invocation_context(
+      agent=agent
+  )
+  # Add events from both current agent and other agent
+  events = [
+      Event(
+          invocation_id="inv1",
+          author="current_agent",
+          content=types.ModelContent("My own message"),
+      ),
+      Event(
+          invocation_id="inv2",
+          author="other_agent",
+          content=types.ModelContent("Other agent message"),
+      ),
+  ]
+  invocation_context.session.events = events
+
+  # Process the request
+  async for _ in request_processor.run_async(invocation_context, llm_request):
+    pass
+
+  # Verify current agent's message stays as model role
+  # and other agent's message is converted to user context
+  assert len(llm_request.contents) == 2
+  assert llm_request.contents[0] == types.ModelContent("My own message")
+  assert llm_request.contents[1].role == "user"
+  assert llm_request.contents[1].parts == [
+      types.Part(text="For context:"),
+      types.Part(text="[other_agent] said: Other agent message"),
+  ]
+
+
+@pytest.mark.asyncio
+async def test_user_messages_preserved():
+  """Test that user messages are preserved as-is."""
+  agent = Agent(model="gemini-2.5-flash", name="current_agent")
+  llm_request = LlmRequest(model="gemini-2.5-flash")
+  invocation_context = await testing_utils.create_invocation_context(
+      agent=agent
+  )
+  # Add user message
+  user_event = Event(
+      invocation_id="inv1",
+      author="user",
+      content=types.UserContent("User message"),
+  )
+  invocation_context.session.events = [user_event]
+
+  # Process the request
+  async for _ in request_processor.run_async(invocation_context, llm_request):
+    pass
+
+  # Verify user message is preserved exactly
+  assert len(llm_request.contents) == 1
+  assert llm_request.contents[0] == types.UserContent("User message")