tools_dict session-wide key causes cross-agent tool dispatch errors in parallel

[Valwolfor]

temp:tools_dict session-wide key causes cross-agent tool dispatch errors in parallel graph_flow

Version

google-adk 2.0.0a2

Description

When multiple LlmAgents with tools run in parallel inside a graph_flow
(fan-out topology), all agents write their resolved tools to the same flat
session-wide key temp:tools_dict. Last-writer wins. When execute_tools
reads that key to dispatch a function call, it may pick up a different
agent's tools_dict, raising:

ValueError: Tool 'X' not found

Root cause

_call_llm_node.call_llm stores the resolved tools dict at:

invocation_context.session.state["temp:tools_dict"] = tools_dict

In a parallel graph_flow, multiple agent tasks run concurrently and all
write to this same key. _execute_tools_node.execute_tools then reads
session.state["temp:tools_dict"] — whichever agent wrote last wins,
dispatching function calls against the wrong agent's tools.

A ContextVar does not fix this: _process_agent_tools runs in the
call_llm Task while execute_tools runs in a sibling Task (not a
child). ContextVar.set() in one Task never propagates to sibling Tasks.

Workaround

Patch _process_agent_tools to snapshot the resolved tools_dict per agent
in a module-level dict keyed by agent name, then patch
handle_function_call_list_async to look up the correct dict before
forwarding. asyncio is single-threaded so there are no true write races.

_tools_by_agent: dict[str, dict] = {}

# In patched _process_agent_tools:
agent_name = invocation_context.agent.name
_tools_by_agent[agent_name] = dict(llm_request.tools_dict)

# In patched handle_function_call_list_async:
agent_name = invocation_context.agent.name
if agent_name in _tools_by_agent:
    tools_dict = _tools_by_agent[agent_name]

Steps to reproduce

1. Define a graph_flow with fan-out to 2+ LlmAgents, each with different tools.
2. Send a message that triggers tool calls from multiple agents in the same turn.
3. Observe ValueError: Tool 'X' not found from the agent whose tools_dict was overwritten.