feat: Define an AgentState to be used for resuming agent invocation

PiperOrigin-RevId: 811414736

src/google/adk/agents/base_agent.py

@@ -66,6 +66,15 @@ AfterAgentCallback: TypeAlias = Union[
 SelfAgent = TypeVar('SelfAgent', bound='BaseAgent')
 
 
+@experimental
+class BaseAgentState(BaseModel):
+  """Base class for all agent states."""
+
+  model_config = ConfigDict(
+      extra='forbid',
+  )
+
+
 class BaseAgent(BaseModel):
   """Base class for all agents in Agent Development Kit."""
 

src/google/adk/agents/loop_agent.py

@@ -21,7 +21,6 @@ from typing import AsyncGenerator
 from typing import ClassVar
 from typing import Dict
 from typing import Optional
-from typing import Type
 
 from typing_extensions import override
 
@@ -30,10 +29,22 @@ from ..events.event import Event
 from ..utils.context_utils import Aclosing
 from ..utils.feature_decorator import experimental
 from .base_agent import BaseAgent
+from .base_agent import BaseAgentState
 from .base_agent_config import BaseAgentConfig
 from .loop_agent_config import LoopAgentConfig
 
 
+@experimental
+class LoopAgentState(BaseAgentState):
+  """State for LoopAgent."""
+
+  current_sub_agent: str = ''
+  """The name of the current sub-agent to run in the loop."""
+
+  times_looped: int = 0
+  """The number of times the loop agent has looped."""
+
+
 class LoopAgent(BaseAgent):
   """A shell agent that run its sub-agents in a loop.
 

src/google/adk/agents/sequential_agent.py

@@ -24,13 +24,23 @@ from typing_extensions import override
 
 from ..events.event import Event
 from ..utils.context_utils import Aclosing
+from ..utils.feature_decorator import experimental
 from .base_agent import BaseAgent
-from .base_agent import BaseAgentConfig
+from .base_agent import BaseAgentState
+from .base_agent_config import BaseAgentConfig
 from .invocation_context import InvocationContext
 from .llm_agent import LlmAgent
 from .sequential_agent_config import SequentialAgentConfig
 
 
+@experimental
+class SequentialAgentState(BaseAgentState):
+  """State for SequentialAgent."""
+
+  current_sub_agent: str = ''
+  """The name of the current sub-agent to run."""
+
+
 class SequentialAgent(BaseAgent):
   """A shell agent that runs its sub-agents in sequence."""
 

src/google/adk/events/event_actions.py

@@ -14,6 +14,7 @@
 
 from __future__ import annotations
 
+from typing import Any
 from typing import Optional
 
 from google.genai.types import Content
@@ -95,3 +96,11 @@ class EventActions(BaseModel):
 
   compaction: Optional[EventCompaction] = None
   """The compaction of the events."""
+
+  end_of_agent: Optional[bool] = None
+  """If true, the current agent has finished its current run. Note that there
+  can be multiple events with end_of_agent=True for the same agent within one
+  invocation when there is a loop."""
+
+  agent_state: Optional[dict[str, Any]] = None
+  """The agent state at the current event."""