Fix usage metadata write and empty response

src/google/adk/sessions/database_session_service.py

@@ -46,6 +46,7 @@
 from sqlalchemy.orm import Mapped
 from sqlalchemy.orm import mapped_column
 from sqlalchemy.orm import relationship
+from sqlalchemy.orm.attributes import flag_modified
 from sqlalchemy.schema import MetaData
 from sqlalchemy.types import DateTime
 from sqlalchemy.types import PickleType
@@ -335,11 +336,20 @@ def from_event(cls, session: Session, event: Event) -> StorageEvent:
       )
     if event.custom_metadata:
       storage_event.custom_metadata = event.custom_metadata
-    if event.usage_metadata:
-      storage_event.usage_metadata = event.usage_metadata.model_dump(
-          exclude_none=True, mode="json"
-      )
-    if event.citation_metadata:
+
+    if hasattr(event, "usage_metadata") and event.usage_metadata is not None:
+      try:
+        usage_meta = event.usage_metadata
+        if hasattr(usage_meta, "model_dump"):
+          storage_event.usage_metadata = usage_meta.model_dump(
+              exclude_none=False, mode="json"
+          )
+      except Exception as e:
+        logger.error(
+            f"[StorageEvent.from_event] Error while saving usage_metadata: {e}"
+        )
+
+    if hasattr(event, "citation_metadata") and event.citation_metadata:
       storage_event.citation_metadata = event.citation_metadata.model_dump(
           exclude_none=True, mode="json"
       )
@@ -727,7 +737,15 @@ async def append_event(self, session: Session, event: Event) -> Event:
       else:
         update_time = datetime.fromtimestamp(event.timestamp)
       storage_session.update_time = update_time
-      sql_session.add(StorageEvent.from_event(session, event))
+      storage_event = StorageEvent.from_event(session, event)
+
+      sql_session.add(storage_event)
+
+      # Forçar SQLAlchemy a detectar mudanças em campos MutableDict/DynamicJSON
+      if storage_event.usage_metadata is not None:
+        flag_modified(storage_event, "usage_metadata")
+      if storage_event.citation_metadata is not None:
+        flag_modified(storage_event, "citation_metadata")
 
       await sql_session.commit()
       await sql_session.refresh(storage_session)

src/google/adk/tools/agent_tool.py

@@ -14,6 +14,8 @@
 
 from __future__ import annotations
 
+import json
+import logging
 from typing import Any
 from typing import TYPE_CHECKING
 
@@ -23,7 +25,9 @@
 
 from . import _automatic_function_calling_util
 from ..agents.common_configs import AgentRefConfig
+from ..events.event import Event
 from ..memory.in_memory_memory_service import InMemoryMemoryService
+from ..sessions import Session
 from ..utils.context_utils import Aclosing
 from ._forwarding_artifact_service import ForwardingArtifactService
 from .base_tool import BaseTool
@@ -34,6 +38,8 @@
 if TYPE_CHECKING:
   from ..agents.base_agent import BaseAgent
 
+logger = logging.getLogger(__name__)
+
 
 class AgentTool(BaseTool):
   """A tool that wraps an agent.
@@ -136,7 +142,11 @@ async def run_async(
     else:
       content = types.Content(
           role='user',
-          parts=[types.Part.from_text(text=args['request'])],
+          parts=[
+              types.Part.from_text(
+                  text=str(args) if isinstance(args, str) else json.dumps(args)
+              )
+          ],
       )
     invocation_context = tool_context._invocation_context
     parent_app_name = (
@@ -161,40 +171,85 @@ async def run_async(
     state_dict = {
         k: v
         for k, v in tool_context.state.to_dict().items()
-        if not k.startswith('_adk')  # Filter out adk internal states
+        if not k.startswith('_adk')
     }
-    session = await runner.session_service.create_session(
+    sub_agent_session = await runner.session_service.create_session(
         app_name=child_app_name,
         user_id=tool_context._invocation_context.user_id,
         state=state_dict,
     )
 
-    last_content = None
+    # Collect all text chunks from streaming response instead of just last content
+    chunks: list[str] = []
+    sub_agent_events = []
+
+    def iter_text_parts(parts):
+      """Safely iterate over parts and extract text, skipping None values."""
+      for p in parts or []:
+        if hasattr(p, 'text') and p.text is not None:
+          yield p.text
+
     async with Aclosing(
         runner.run_async(
-            user_id=session.user_id, session_id=session.id, new_message=content
+            user_id=sub_agent_session.user_id,
+            session_id=sub_agent_session.id,
+            new_message=content,
         )
     ) as agen:
       async for event in agen:
-        # Forward state delta to parent session.
         if event.actions.state_delta:
           tool_context.state.update(event.actions.state_delta)
+        # Collect text chunks from all events, not just the last one
         if event.content:
-          last_content = event.content
+          chunks.extend(iter_text_parts(event.content.parts))
+        sub_agent_events.append(event)
+
+    if sub_agent_events and hasattr(tool_context, '_invocation_context'):
+      main_session = tool_context._invocation_context.session
+      if main_session and hasattr(
+          tool_context._invocation_context, 'session_service'
+      ):
+        session_service = tool_context._invocation_context.session_service
+        parent_agent_name = (
+            tool_context._invocation_context.agent.name
+            if hasattr(tool_context._invocation_context, 'agent')
+            else 'root_agent'
+        )
+
+        for sub_event in sub_agent_events:
+
+          try:
+            if hasattr(sub_event, 'branch') and sub_event.branch:
+              event_branch = sub_event.branch
+            else:
+              event_branch = f'{parent_agent_name}.{self.agent.name}'
+
+            copied_event = sub_event.model_copy(update={'branch': event_branch})
+
+            await session_service.append_event(main_session, copied_event)
+          except Exception as e:
+            logger.warning(
+                "Error copying sub-agent event from '%s' to main session: %s",
+                self.agent.name,
+                e,
+            )
 
     # Clean up runner resources (especially MCP sessions)
     # to avoid "Attempted to exit cancel scope in a different task" errors
     await runner.close()
 
-    if not last_content:
+    # Merge all collected chunks into final text
+    merged_text = ''.join(chunks)
+
+    if not merged_text:
       return ''
-    merged_text = '\n'.join(p.text for p in last_content.parts if p.text)
     if isinstance(self.agent, LlmAgent) and self.agent.output_schema:
       tool_result = self.agent.output_schema.model_validate_json(
           merged_text
       ).model_dump(exclude_none=True)
     else:
       tool_result = merged_text
+
     return tool_result
 
   @override