fix: respect A2A Message.role in inbound event conversion (#5186)

convert_a2a_message_to_event() hard-coded role='model' on the GenAI
Content it produced, ignoring the A2A Message.role field. This caused
Role.user messages to be misattributed as model output.

Additionally, the task-history fallback in convert_a2a_task_to_event()
blindly took history[-1] without checking Message.role, so a trailing
user message could be restored as agent output.

Changes:
- Add a2a_role_to_genai_role() helper in utils.py (Role.agent→'model',
  Role.user→'user').
- event_converter.py: use the helper instead of hard-coded 'model' in
  convert_a2a_message_to_event(); filter history fallback to agent-role
  messages only.
- to_adk_event.py: add role parameter to _create_event(); pass mapped
  role from convert_a2a_message_to_event().
- Regression tests for role restoration and history fallback.

Author: giulio-leone

src/google/adk/a2a/converters/event_converter.py

@@ -37,6 +37,8 @@
 from google.adk.platform import uuid as platform_uuid
 from google.genai import types as genai_types
 
+from .utils import a2a_role_to_genai_role
+
 from ...agents.invocation_context import InvocationContext
 from ...events.event import Event
 from ...flows.llm_flows.functions import REQUEST_EUC_FUNCTION_CALL_NAME
@@ -238,7 +240,13 @@ def convert_a2a_task_to_event(
     ):
       message = a2a_task.status.message
     elif a2a_task.history:
-      message = a2a_task.history[-1]
+      # Only pick agent-role messages from history; a trailing user
+      # message should not be misattributed as agent output.
+      agent_messages = [
+          m for m in a2a_task.history if m.role == Role.agent
+      ]
+      if agent_messages:
+        message = agent_messages[-1]
 
     # Convert message if available
     if message:
@@ -292,6 +300,8 @@ def convert_a2a_message_to_event(
   if a2a_message is None:
     raise ValueError("A2A message cannot be None")
 
+  genai_role = a2a_role_to_genai_role(a2a_message.role)
+
   if not a2a_message.parts:
     logger.warning(
         "A2A message has no parts, creating event with empty content"
@@ -304,7 +314,7 @@ def convert_a2a_message_to_event(
         ),
         author=author or "a2a agent",
         branch=invocation_context.branch if invocation_context else None,
-        content=genai_types.Content(role="model", parts=[]),
+        content=genai_types.Content(role=genai_role, parts=[]),
     )
 
   try:
@@ -358,7 +368,7 @@ def convert_a2a_message_to_event(
         if long_running_tool_ids
         else None,
         content=genai_types.Content(
-            role="model",
+            role=genai_role,
             parts=output_parts,
         ),
     )

src/google/adk/a2a/converters/to_adk_event.py

@@ -39,6 +39,7 @@
 from .part_converter import A2APartToGenAIPartConverter
 from .part_converter import convert_a2a_part_to_genai_part
 from .utils import _get_adk_metadata_key
+from .utils import a2a_role_to_genai_role
 
 # Logger
 logger = logging.getLogger("google_adk." + __name__)
@@ -177,6 +178,7 @@ def _create_event(
     actions: Optional[EventActions] = None,
     long_running_function_ids: Optional[set[str]] = None,
     partial: bool = False,
+    role: str = "model",
 ) -> Optional[Event]:
   """Creates an ADK event from parts and metadata."""
   event_actions = actions or EventActions()
@@ -199,7 +201,7 @@ def _create_event(
       ),
       content=(
           genai_types.Content(
-              role="model",
+              role=role,
               parts=output_parts,
           )
           if output_parts
@@ -380,6 +382,7 @@ def convert_a2a_message_to_event(
         invocation_context,
         author,
         _extract_event_actions(a2a_message.metadata),
+        role=a2a_role_to_genai_role(a2a_message.role),
     )
 
   except Exception as e:

src/google/adk/a2a/converters/utils.py

@@ -14,10 +14,37 @@
 
 from __future__ import annotations
 
+from typing import Union
+
+from a2a.types import Role
+
 ADK_METADATA_KEY_PREFIX = "adk_"
 ADK_CONTEXT_ID_PREFIX = "ADK"
 ADK_CONTEXT_ID_SEPARATOR = "/"
 
+_A2A_ROLE_TO_GENAI_ROLE = {
+    Role.agent: "model",
+    Role.user: "user",
+}
+
+
+def a2a_role_to_genai_role(role: Union[Role, str]) -> str:
+  """Maps an A2A Role to the corresponding GenAI content role.
+
+  Args:
+    role: An A2A Role enum value or its string equivalent.
+
+  Returns:
+    ``"model"`` for ``Role.agent``, ``"user"`` for ``Role.user``.
+    Falls back to ``"model"`` for unrecognised values.
+  """
+  if isinstance(role, str):
+    try:
+      role = Role(role)
+    except ValueError:
+      return "model"
+  return _A2A_ROLE_TO_GENAI_ROLE.get(role, "model")
+
 
 def _get_adk_metadata_key(key: str) -> str:
   """Gets the A2A event metadata key for the given key.

tests/unittests/a2a/converters/test_event_converter.py

@@ -697,6 +697,7 @@ def test_convert_a2a_task_to_event_with_history_message(self):
 
     # Create mock message and task
     mock_message = Mock(spec=Message)
+    mock_message.role = Role.agent
     mock_task = Mock(spec=Task)
     mock_task.artifacts = None
     mock_task.status = None
@@ -799,6 +800,7 @@ def test_convert_a2a_message_to_event_success(self):
     mock_convert_part = Mock(return_value=mock_genai_part)
 
     mock_message = Mock(spec=Message, parts=[mock_a2a_part])
+    mock_message.role = Role.agent
 
     result = convert_a2a_message_to_event(
         mock_message,
@@ -828,6 +830,7 @@ def test_convert_a2a_message_to_event_with_multiple_parts_returned(self):
     mock_convert_part = Mock(return_value=[mock_genai_part1, mock_genai_part2])
 
     mock_message = Mock(spec=Message, parts=[mock_a2a_part])
+    mock_message.role = Role.agent
 
     # Act
     result = convert_a2a_message_to_event(
@@ -850,6 +853,7 @@ def test_convert_a2a_message_to_event_with_long_running_tools(self):
 
     # Create mock parts and message
     mock_message = Mock(spec=Message, parts=[Mock()])
+    mock_message.role = Role.agent
 
     # Mock the part conversion to return None to simulate long-running tool detection logic
     mock_convert_part = Mock(return_value=None)
@@ -876,6 +880,7 @@ def test_convert_a2a_message_to_event_empty_parts(self):
     from google.adk.a2a.converters.event_converter import convert_a2a_message_to_event
 
     mock_message = Mock(spec=Message, parts=[])
+    mock_message.role = Role.agent
 
     result = convert_a2a_message_to_event(
         mock_message, "test-author", self.mock_invocation_context
@@ -903,6 +908,7 @@ def test_convert_a2a_message_to_event_part_conversion_fails(self):
     mock_convert_part = Mock(return_value=None)
 
     mock_message = Mock(spec=Message, parts=[mock_a2a_part])
+    mock_message.role = Role.agent
 
     result = convert_a2a_message_to_event(
         mock_message,
@@ -935,6 +941,7 @@ def test_convert_a2a_message_to_event_part_conversion_exception(self):
     )
 
     mock_message = Mock(spec=Message, parts=[mock_a2a_part1, mock_a2a_part2])
+    mock_message.role = Role.agent
 
     result = convert_a2a_message_to_event(
         mock_message,
@@ -956,6 +963,7 @@ def test_convert_a2a_message_to_event_missing_tool_id(self):
 
     # Create mock parts and message
     mock_message = Mock(spec=Message, parts=[Mock()])
+    mock_message.role = Role.agent
 
     # Mock the part conversion to return None
     mock_convert_part = Mock(return_value=None)
@@ -980,6 +988,7 @@ def test_convert_a2a_message_to_event_default_author(self, mock_uuid):
     from google.adk.a2a.converters.event_converter import convert_a2a_message_to_event
 
     mock_message = Mock(spec=Message, parts=[])
+    mock_message.role = Role.agent
 
     # Mock UUID generation
     mock_uuid.return_value = "generated-uuid"
@@ -990,3 +999,132 @@ def test_convert_a2a_message_to_event_default_author(self, mock_uuid):
     assert result.author == "a2a agent"
     assert result.branch is None
     assert result.invocation_id == "generated-uuid"
+
+
+class TestRoleMappingRegression:
+  """Regression tests for issue #5186: role mapping in A2A→ADK conversion."""
+
+  def setup_method(self):
+    """Set up test fixtures."""
+    self.mock_invocation_context = Mock(spec=InvocationContext)
+    self.mock_invocation_context.invocation_id = "test-invocation-id"
+    self.mock_invocation_context.branch = "test-branch"
+
+  def test_user_role_message_maps_to_user_content_role(self):
+    """A2A Role.user must produce content.role='user', not 'model'."""
+    from a2a.types import Part
+    from a2a.types import TextPart
+    from google.adk.a2a.converters.event_converter import convert_a2a_message_to_event
+
+    message = Message(
+        message_id="msg-1",
+        role=Role.user,
+        parts=[Part(root=TextPart(text="user says hi"))],
+    )
+
+    event = convert_a2a_message_to_event(
+        message, "test-author", self.mock_invocation_context
+    )
+
+    assert event.content.role == "user"
+
+  def test_agent_role_message_maps_to_model_content_role(self):
+    """A2A Role.agent must produce content.role='model'."""
+    from a2a.types import Part
+    from a2a.types import TextPart
+    from google.adk.a2a.converters.event_converter import convert_a2a_message_to_event
+
+    message = Message(
+        message_id="msg-1",
+        role=Role.agent,
+        parts=[Part(root=TextPart(text="agent reply"))],
+    )
+
+    event = convert_a2a_message_to_event(
+        message, "test-author", self.mock_invocation_context
+    )
+
+    assert event.content.role == "model"
+
+  def test_empty_parts_user_message_preserves_user_role(self):
+    """Even with empty parts, Role.user must map to content.role='user'."""
+    from google.adk.a2a.converters.event_converter import convert_a2a_message_to_event
+
+    message = Message(message_id="msg-1", role=Role.user, parts=[])
+
+    event = convert_a2a_message_to_event(
+        message, "test-author", self.mock_invocation_context
+    )
+
+    assert event.content.role == "user"
+
+  def test_task_history_fallback_skips_trailing_user_message(self):
+    """History fallback must not return a user-role trailing message."""
+    from a2a.types import Part
+    from a2a.types import TaskStatus
+    from a2a.types import TextPart
+
+    agent_msg = Message(
+        message_id="m1",
+        role=Role.agent,
+        parts=[Part(root=TextPart(text="agent reply"))],
+    )
+    user_msg = Message(
+        message_id="m2",
+        role=Role.user,
+        parts=[Part(root=TextPart(text="follow-up question"))],
+    )
+
+    task = Task(
+        id="task-1",
+        status=TaskStatus(
+            state=TaskState.submitted, timestamp="2024-01-01T00:00:00Z"
+        ),
+        context_id="ctx-1",
+        history=[agent_msg, user_msg],
+    )
+
+    with patch(
+        "google.adk.a2a.converters.event_converter.convert_a2a_message_to_event"
+    ) as mock_convert:
+      mock_event = Mock(spec=Event)
+      mock_convert.return_value = mock_event
+
+      convert_a2a_task_to_event(
+          task, "test-author", self.mock_invocation_context
+      )
+
+      # Must be called with the agent message, not the trailing user message
+      mock_convert.assert_called_once()
+      called_message = mock_convert.call_args[0][0]
+      assert called_message.role == Role.agent
+      assert called_message.message_id == "m1"
+
+  def test_task_history_fallback_only_user_messages_creates_minimal_event(self):
+    """History with only user messages must produce a minimal event."""
+    from a2a.types import Part
+    from a2a.types import TaskStatus
+    from a2a.types import TextPart
+
+    user_msg = Message(
+        message_id="m1",
+        role=Role.user,
+        parts=[Part(root=TextPart(text="question"))],
+    )
+
+    task = Task(
+        id="task-1",
+        status=TaskStatus(
+            state=TaskState.submitted, timestamp="2024-01-01T00:00:00Z"
+        ),
+        context_id="ctx-1",
+        history=[user_msg],
+    )
+
+    result = convert_a2a_task_to_event(
+        task, "test-author", self.mock_invocation_context
+    )
+
+    # No agent message to convert → minimal event (no content)
+    assert result.author == "test-author"
+    assert result.content is None

tests/unittests/a2a/converters/test_to_adk.py

@@ -418,3 +418,58 @@ def test_convert_a2a_artifact_update_to_event_none(self):
     """Test convert_a2a_artifact_update_to_event with None."""
     with pytest.raises(ValueError, match="A2A artifact update cannot be None"):
       convert_a2a_artifact_update_to_event(None)
+
+
+class TestToAdkRoleMappingRegression:
+  """Regression tests for issue #5186: role mapping in to_adk_event."""
+
+  def setup_method(self):
+    self.mock_context = Mock(spec=InvocationContext)
+    self.mock_context.invocation_id = "test-invocation"
+    self.mock_context.branch = "test-branch"
+
+  def test_user_role_message_maps_to_user_content_role(self):
+    """A2A Role.user must produce content.role='user', not 'model'."""
+    from a2a.types import Role
+
+    a2a_part = Mock(spec=A2APart)
+    a2a_part.root = Mock(spec=TextPart)
+    a2a_part.root.metadata = {}
+    message = Message(
+        message_id="msg-1",
+        role=Role.user,
+        parts=[a2a_part],
+    )
+
+    mock_genai_part = genai_types.Part.from_text(text="user says hi")
+    event = convert_a2a_message_to_event(
+        message,
+        author="test-author",
+        invocation_context=self.mock_context,
+        part_converter=Mock(return_value=[mock_genai_part]),
+    )
+
+    assert event.content.role == "user"
+
+  def test_agent_role_message_maps_to_model_content_role(self):
+    """A2A Role.agent must produce content.role='model'."""
+    from a2a.types import Role
+
+    a2a_part = Mock(spec=A2APart)
+    a2a_part.root = Mock(spec=TextPart)
+    a2a_part.root.metadata = {}
+    message = Message(
+        message_id="msg-1",
+        role=Role.agent,
+        parts=[a2a_part],
+    )
+
+    mock_genai_part = genai_types.Part.from_text(text="agent reply")
+    event = convert_a2a_message_to_event(
+        message,
+        author="test-author",
+        invocation_context=self.mock_context,
+        part_converter=Mock(return_value=[mock_genai_part]),
+    )
+
+    assert event.content.role == "model"