feat(cli): Implement save-session-on-runtime feature for periodic session checkpointing

src/google/adk/cli/cli.py

@@ -14,6 +14,7 @@
 
 from __future__ import annotations
 
+import asyncio
 from datetime import datetime
 from pathlib import Path
 from typing import Optional
@@ -69,25 +70,25 @@ async def run_input_file(
       memory_service=memory_service,
       credential_service=credential_service,
   )
-  with open(input_path, 'r', encoding='utf-8') as f:
+  with open(input_path, "r", encoding="utf-8") as f:
     input_file = InputFile.model_validate_json(f.read())
-  input_file.state['_time'] = datetime.now().isoformat()
+  input_file.state["_time"] = datetime.now().isoformat()
 
   session = await session_service.create_session(
       app_name=app_name, user_id=user_id, state=input_file.state
   )
   for query in input_file.queries:
-    click.echo(f'[user]: {query}')
-    content = types.Content(role='user', parts=[types.Part(text=query)])
+    click.echo(f"[user]: {query}")
+    content = types.Content(role="user", parts=[types.Part(text=query)])
     async with Aclosing(
         runner.run_async(
             user_id=session.user_id, session_id=session.id, new_message=content
         )
     ) as agen:
       async for event in agen:
         if event.content and event.content.parts:
-          if text := ''.join(part.text or '' for part in event.content.parts):
-            click.echo(f'[{event.author}]: {text}')
+          if text := "".join(part.text or "" for part in event.content.parts):
+            click.echo(f"[{event.author}]: {text}")
   return session
 
 
@@ -98,6 +99,9 @@ async def run_interactively(
     session_service: BaseSessionService,
     credential_service: BaseCredentialService,
     memory_service: Optional[BaseMemoryService] = None,
+    save_session_on_runtime: bool = False,
+    interval: int = 60,
+    agent_root: Optional[Path] = None,
 ) -> None:
   app = (
       root_agent_or_app
@@ -111,25 +115,74 @@ async def run_interactively(
       memory_service=memory_service,
       credential_service=credential_service,
   )
-  while True:
-    query = input('[user]: ')
-    if not query or not query.strip():
-      continue
-    if query == 'exit':
-      break
-    async with Aclosing(
-        runner.run_async(
-            user_id=session.user_id,
-            session_id=session.id,
-            new_message=types.Content(
-                role='user', parts=[types.Part(text=query)]
-            ),
-        )
-    ) as agen:
-      async for event in agen:
-        if event.content and event.content.parts:
-          if text := ''.join(part.text or '' for part in event.content.parts):
-            click.echo(f'[{event.author}]: {text}')
+
+  # Background task for periodic session saving
+  save_task: Optional[asyncio.Task[None]] = None  
+
+  async def _periodic_save_session() -> None:  
+    """Periodically save the session to disk every interval seconds."""
+    nonlocal session, save_task
+    try:
+      while True:
+        await asyncio.sleep(interval)
+        click.echo(f"interval : {interval}")
+
+        if save_session_on_runtime and agent_root:
+          try:
+            current_session = await session_service.get_session(
+                app_name=session.app_name,
+                user_id=session.user_id,
+                session_id=session.id,
+            )
+
+            if current_session:
+              runtime_session_path = (
+                  agent_root / ".adk" / "runtime_session.json"
+              )
+              runtime_session_path.parent.mkdir(parents=True, exist_ok=True)
+              runtime_session_path.write_text(
+                  current_session.model_dump_json(
+                      indent=2, exclude_none=True, by_alias=True
+                  ),
+                  encoding="utf-8",
+              )
+          except Exception:
+            pass
+    except asyncio.CancelledError:
+      pass
+
+  # Start the periodic save task if enabled
+  if save_session_on_runtime and agent_root:
+    save_task = asyncio.create_task(_periodic_save_session())
+
+  try:
+    while True:
+      query = input("[user]: ")
+      if not query or not query.strip():
+        continue
+      if query == "exit":
+        break
+      async with Aclosing(
+          runner.run_async(
+              user_id=session.user_id,
+              session_id=session.id,
+              new_message=types.Content(
+                  role="user", parts=[types.Part(text=query)]
+              ),
+          )
+      ) as agen:
+        async for event in agen:
+          if event.content and event.content.parts:
+            if text := "".join(part.text or "" for part in event.content.parts):
+              click.echo(f"[{event.author}]: {text}")
+  finally:
+    if save_task:
+      save_task.cancel()
+      try:
+        await save_task
+      except asyncio.CancelledError:
+        pass
+
   await runner.close()
 
 
@@ -140,6 +193,8 @@ async def run_cli(
     input_file: Optional[str] = None,
     saved_session_file: Optional[str] = None,
     save_session: bool,
+    save_session_on_runtime: bool,
+    interval: int,
     session_id: Optional[str] = None,
     session_service_uri: Optional[str] = None,
     artifact_service_uri: Optional[str] = None,
@@ -167,7 +222,7 @@ async def run_cli(
   agent_parent_path = Path(agent_parent_dir).resolve()
   agent_root = agent_parent_path / agent_folder_name
   load_services_module(str(agent_root))
-  user_id = 'test_user'
+  user_id = "test_user"
 
   agents_dir = str(agent_parent_path)
   agent_loader = AgentLoader(agents_dir=agents_dir)
@@ -179,7 +234,7 @@ async def run_cli(
   if isinstance(agent_or_app, App) and agent_or_app.name != agent_folder_name:
     app_name_to_dir = {agent_or_app.name: agent_folder_name}
 
-  if not is_env_enabled('ADK_DISABLE_LOAD_DOTENV'):
+  if not is_env_enabled("ADK_DISABLE_LOAD_DOTENV"):
     envs.load_dotenv_for_agent(agent_folder_name, agents_dir)
 
   # Create session and artifact services using factory functions.
@@ -211,8 +266,8 @@ def _print_event(event) -> None:
     text_parts = [part.text for part in content.parts if part.text]
     if not text_parts:
       return
-    author = event.author or 'system'
-    click.echo(f'[{author}]: {"".join(text_parts)}')
+    author = event.author or "system"
+    click.echo(f"[{author}]: {''.join(text_parts)}")
 
   if input_file:
     session = await run_input_file(
@@ -227,7 +282,7 @@ def _print_event(event) -> None:
     )
   elif saved_session_file:
     # Load the saved session from file
-    with open(saved_session_file, 'r', encoding='utf-8') as f:
+    with open(saved_session_file, "r", encoding="utf-8") as f:
       loaded_session = Session.model_validate_json(f.read())
 
     # Create a new session in the service, copying state from the file
@@ -252,22 +307,54 @@ def _print_event(event) -> None:
         memory_service=memory_service,
     )
   else:
-    session = await session_service.create_session(
-        app_name=session_app_name, user_id=user_id
-    )
-    click.echo(f'Running agent {agent_or_app.name}, type exit to exit.')
+    # Check for runtime saved session
+    runtime_session_path = agent_root / ".adk" / "runtime_session.json"
+    if runtime_session_path.exists():
+      try:
+        with open(runtime_session_path, "r", encoding="utf-8") as f:
+          loaded_session = Session.model_validate_json(f.read())
+
+        # Create a new session in the service, copying state from the file
+        session = await session_service.create_session(
+            app_name=session_app_name,
+            user_id=user_id,
+            state=loaded_session.state if loaded_session else None,
+        )
+
+        # Append events from the file to the new session and display them
+        if loaded_session:
+          for event in loaded_session.events:
+            await session_service.append_event(session, event)
+            _print_event(event)
+
+        click.echo(f"Loaded runtime session from {runtime_session_path}")
+      except Exception as e:
+        click.echo(f"Warning: Failed to load runtime session: {e}")
+        # Fall back to creating a new session
+        session = await session_service.create_session(
+            app_name=session_app_name, user_id=user_id
+        )
+    else:
+      session = await session_service.create_session(
+          app_name=session_app_name, user_id=user_id
+      )
+
+    click.echo(f"Running agent {agent_or_app.name}, type exit to exit.")
     await run_interactively(
         agent_or_app,
         artifact_service,
         session,
         session_service,
         credential_service,
         memory_service=memory_service,
+        save_session_on_runtime=True,
+        interval=interval,
+        agent_root=agent_root,
     )
 
   if save_session:
-    session_id = session_id or input('Session ID to save: ')
-    session_path = agent_root / f'{session_id}.session.json'
+    session_id = session_id or input("Session ID to save: ")
+    session_path = agent_root / f"{session_id}.session.json"
 
     # Fetch the session again to get all the details.
     session = await session_service.get_session(
@@ -277,7 +364,7 @@ def _print_event(event) -> None:
     )
     session_path.write_text(
         session.model_dump_json(indent=2, exclude_none=True, by_alias=True),
-        encoding='utf-8',
+        encoding="utf-8",
     )
 
-    print('Session saved to', session_path)
+    print("Session saved to", session_path)

src/google/adk/cli/cli_tools_click.py

@@ -605,6 +605,24 @@ def wrapper(*args, **kwargs):
 @main.command("run", cls=HelpfulCommand)
 @feature_options()
 @adk_services_options(default_use_local_storage=True)
+@click.option(
+    "--interval",
+    type=int,
+    default=60,
+    show_default=True,
+    help=(
+        "Autosave interval in seconds (only used if --save_session_on_runtime"
+        " is set)."
+    ),
+)
+@click.option(
+    "--save_session_on_runtime",
+    type=bool,
+    is_flag=True,
+    show_default=True,
+    default=False,
+    help="Optional. Whether to save the session to a json file on runtime.",
+)
 @click.option(
     "--save_session",
     type=bool,
@@ -653,17 +671,19 @@ def wrapper(*args, **kwargs):
         exists=True, dir_okay=True, file_okay=False, resolve_path=True
     ),
 )
-def cli_run(
+def cli_run(  # type: ignore[misc]
     agent: str,
     save_session: bool,
+    save_session_on_runtime: bool,
+    interval: int,
     session_id: Optional[str],
     replay: Optional[str],
     resume: Optional[str],
     session_service_uri: Optional[str] = None,
     artifact_service_uri: Optional[str] = None,
     memory_service_uri: Optional[str] = None,
     use_local_storage: bool = True,
-):
+) -> None:  
   """Runs an interactive CLI for a certain agent.
 
   AGENT: The path to the agent source code folder.
@@ -684,6 +704,8 @@ def cli_run(
           input_file=replay,
           saved_session_file=resume,
           save_session=save_session,
+          save_session_on_runtime=save_session_on_runtime,
+          interval=interval,
           session_id=session_id,
           session_service_uri=session_service_uri,
           artifact_service_uri=artifact_service_uri,