fix: Let part converters also return multiple parts so they can support more usecases

PiperOrigin-RevId: 830882000

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

@@ -301,13 +301,15 @@ def convert_a2a_message_to_event(
     )
 
   try:
-    parts = []
+    output_parts = []
     long_running_tool_ids = set()
 
     for a2a_part in a2a_message.parts:
       try:
-        part = part_converter(a2a_part)
-        if part is None:
+        parts = part_converter(a2a_part)
+        if not isinstance(parts, list):
+          parts = [parts] if parts else []
+        if not parts:
           logger.warning("Failed to convert A2A part, skipping: %s", a2a_part)
           continue
 
@@ -321,16 +323,18 @@ def convert_a2a_message_to_event(
             )
             is True
         ):
-          long_running_tool_ids.add(part.function_call.id)
+          for part in parts:
+            if part.function_call:
+              long_running_tool_ids.add(part.function_call.id)
 
-        parts.append(part)
+        output_parts.extend(parts)
 
       except Exception as e:
         logger.error("Failed to convert A2A part: %s, error: %s", a2a_part, e)
         # Continue processing other parts instead of failing completely
         continue
 
-    if not parts:
+    if not output_parts:
       logger.warning(
           "No parts could be converted from A2A message %s", a2a_message
       )
@@ -348,7 +352,7 @@ def convert_a2a_message_to_event(
         else None,
         content=genai_types.Content(
             role="model",
-            parts=parts,
+            parts=output_parts,
         ),
     )
 
@@ -387,15 +391,19 @@ def convert_event_to_a2a_message(
     return None
 
   try:
-    a2a_parts = []
+    output_parts = []
     for part in event.content.parts:
-      a2a_part = part_converter(part)
-      if a2a_part:
-        a2a_parts.append(a2a_part)
+      a2a_parts = part_converter(part)
+      if not isinstance(a2a_parts, list):
+        a2a_parts = [a2a_parts] if a2a_parts else []
+      for a2a_part in a2a_parts:
+        output_parts.append(a2a_part)
         _process_long_running_tool(a2a_part, event)
 
-    if a2a_parts:
-      return Message(message_id=str(uuid.uuid4()), role=role, parts=a2a_parts)
+    if output_parts:
+      return Message(
+          message_id=str(uuid.uuid4()), role=role, parts=output_parts
+      )
 
   except Exception as e:
     logger.error("Failed to convert event to status message: %s", e)

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

@@ -22,7 +22,9 @@ import base64
 from collections.abc import Callable
 import json
 import logging
+from typing import List
 from typing import Optional
+from typing import Union
 
 from .utils import _get_adk_metadata_key
 
@@ -53,10 +55,11 @@ A2A_DATA_PART_METADATA_TYPE_EXECUTABLE_CODE = 'executable_code'
 
 
 A2APartToGenAIPartConverter = Callable[
-    [a2a_types.Part], Optional[genai_types.Part]
+    [a2a_types.Part], Union[Optional[genai_types.Part], List[genai_types.Part]]
 ]
 GenAIPartToA2APartConverter = Callable[
-    [genai_types.Part], Optional[a2a_types.Part]
+    [genai_types.Part],
+    Union[Optional[a2a_types.Part], List[a2a_types.Part]],
 ]
 
 

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

@@ -110,12 +110,19 @@ def convert_a2a_request_to_agent_run_request(
   if request.metadata:
     custom_metadata['a2a_metadata'] = request.metadata
 
+  output_parts = []
+  for a2a_part in request.message.parts:
+    genai_parts = part_converter(a2a_part)
+    if not isinstance(genai_parts, list):
+      genai_parts = [genai_parts] if genai_parts else []
+    output_parts.extend(genai_parts)
+
   return AgentRunRequest(
       user_id=_get_user_id(request),
       session_id=request.context_id,
       new_message=genai_types.Content(
           role='user',
-          parts=[part_converter(part) for part in request.message.parts],
+          parts=output_parts,
       ),
       run_config=RunConfig(custom_metadata=custom_metadata),
   )

src/google/adk/agents/remote_a2a_agent.py

@@ -376,9 +376,12 @@ class RemoteA2aAgent(BaseAgent):
         continue
 
       for part in event.content.parts:
-        converted_part = self._genai_part_converter(part)
-        if converted_part:
-          message_parts.append(converted_part)
+        converted_parts = self._genai_part_converter(part)
+        if not isinstance(converted_parts, list):
+          converted_parts = [converted_parts] if converted_parts else []
+
+        if converted_parts:
+          message_parts.extend(converted_parts)
         else:
           logger.warning("Failed to convert part to A2A format: %s", part)