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feat: Implement agent handoff tracking to skip after_agent_callback #4255

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6ceb56c
feat: Implement agent handoff tracking to skip after_agent_callback
jayy-77 Jan 23, 2026
6a1be4e
Merge branch 'main' into agent_handoff_fix
jayy-77 Jan 23, 2026
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12 changes: 8 additions & 4 deletions src/google/adk/agents/base_agent.py
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Original file line number Diff line number Diff line change
Expand Up @@ -297,8 +297,10 @@ async def run_async(
if ctx.end_invocation:
return

if event := await self._handle_after_agent_callback(ctx):
yield event
# Skip after_agent_callback if the agent has handed off to another agent
if not ctx.agent_handoff_occurred:
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@gemini-code-assist gemini-code-assist bot Jan 23, 2026

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high

There's a potential logic issue here. When agent1 hands off to agent2, ctx.agent_handoff_occurred is set to True. This correctly skips the after_agent_callback for agent1. However, agent2 inherits the context with this flag set to True, so its after_agent_callback will also be skipped, which is likely unintended. The callback should only be skipped for the agent that initiates the handoff.

A possible solution is to reset this flag at the beginning of each agent's run. You could add ctx.agent_handoff_occurred = False at the start of the run_async method in this file, after ctx is created. Since this change is outside the current diff, I cannot provide a direct code suggestion for it.

if event := await self._handle_after_agent_callback(ctx):
yield event
Comment on lines +301 to +303
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@gemini-code-assist gemini-code-assist bot Jan 23, 2026

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medium

For better readability, you can combine the nested if statements into a single condition.

      if not ctx.agent_handoff_occurred and (event := await self._handle_after_agent_callback(ctx)):
        yield event


@final
async def run_live(
Expand Down Expand Up @@ -327,8 +329,10 @@ async def run_live(
async for event in agen:
yield event

if event := await self._handle_after_agent_callback(ctx):
yield event
# Skip after_agent_callback if the agent has handed off to another agent
if not ctx.agent_handoff_occurred:
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@gemini-code-assist gemini-code-assist bot Jan 23, 2026

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high

Similar to my comment in run_async, there's a potential logic issue here that would cause the after_agent_callback to be skipped for the receiving agent as well as the transferring agent.

A possible solution is to reset this flag at the beginning of each agent's run. You could add ctx.agent_handoff_occurred = False at the start of the run_live method in this file, after ctx is created. Since this change is outside the current diff, I cannot provide a direct code suggestion for it.

if event := await self._handle_after_agent_callback(ctx):
yield event
Comment on lines +333 to +335
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medium

For better readability, you can combine the nested if statements into a single condition.

      if not ctx.agent_handoff_occurred and (event := await self._handle_after_agent_callback(ctx)):
        yield event


async def _run_async_impl(
self, ctx: InvocationContext
Expand Down
7 changes: 7 additions & 0 deletions src/google/adk/agents/invocation_context.py
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Original file line number Diff line number Diff line change
Expand Up @@ -176,6 +176,13 @@ class InvocationContext(BaseModel):

Set to True in callbacks or tools to terminate this invocation."""

agent_handoff_occurred: bool = False
"""Whether the current agent has handed off control to another agent.

Set to True when an agent transfers control to another agent via the
transfer_to_agent tool. Used to prevent after_agent_callback from running
on the transferring agent after handoff has occurred."""

live_request_queue: Optional[LiveRequestQueue] = None
"""The queue to receive live requests."""

Expand Down
4 changes: 4 additions & 0 deletions src/google/adk/flows/llm_flows/base_llm_flow.py
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Original file line number Diff line number Diff line change
Expand Up @@ -229,6 +229,8 @@ async def run_live(
transfer_to_agent = event.actions.transfer_to_agent
if transfer_to_agent:
logger.debug('Transferring to agent: %s', transfer_to_agent)
# Mark that handoff has occurred so after_agent_callback is skipped
invocation_context.agent_handoff_occurred = True
agent_to_run = self._get_agent_to_run(
invocation_context, transfer_to_agent
)
Expand Down Expand Up @@ -765,6 +767,8 @@ async def _postprocess_handle_function_calls_async(
yield final_event
transfer_to_agent = function_response_event.actions.transfer_to_agent
if transfer_to_agent:
# Mark that handoff has occurred so after_agent_callback is skipped
invocation_context.agent_handoff_occurred = True
agent_to_run = self._get_agent_to_run(
invocation_context, transfer_to_agent
)
Expand Down