Use of PlanReActPlanner with sub-agents #3927

Hi all,
I'm trying to implement PlanReActPlanner with ADK 1.21.0, but I'm having some issues.

My architecture would be the following:

• root_agent with PlanReActPlanner
• subagent_a
• subagent_b

Now, I want to connect subagent_a and subagent_b to router_agent via sub_agents, not tools, because with the latter I have less traceability of what the sub_agents actually do (e.g. they use multiple tools).

I also want the router_agent to think iteratively, always evaluating the sub agents replies and act. E.g. the plan first say to call A, then the result of A is not satisfying (e.g. no documents found in internal documentation) then I use B as a fallback.

How should this be implemented? My feeling is that PlanReActPlanner:

1. is not iterating: it makes one plan and just executes without revising it, or adding actions
2. only works with agents as a tool, not with sub agents. Indeed my sub agents just reply to the user and cannot go back to the router. I tried to force the comeback with:

function_call = FunctionCall(
    args={"agent_name": "root_agent"},
    name="transfer_to_agent",
)
new_part = Part(function_call=function_call)
llm_response.content.parts.append(new_part)

But I get "tool not found" error.