Function handle_a2a_request 

pub fn handle_a2a_request(
    _agent: &CompiledA2aAgent,
    _req: &ChatRequest,
) -> Result<ChatResponse, A2AStub>

Route an A2A call through the existing dataplane::ai_proxy path (DW-114). The transport is the agent’s named upstream, exactly like a regular provider: the A2AAdapter builds the task-submit request, ai_proxy places the call through the upstream, and the response is parsed back to the canonical shape. This function is the seam the dataplane calls for an A2A-routed alias; today it returns an A2AStub error because the adapter intentionally does not own an HTTP client (the transport is the agent’s upstream, driven from dataplane::ai_proxy). The task lifecycle state machine itself is implemented (see TaskStateMachine); this function is the network-call seam, not the state machine.

The scaffold keeps the call-site shape stable so the dataplane path compiles unchanged with or without the feature.