Function spawn_session_with_channels 

pub fn spawn_session_with_channels(
    deps: SessionDeps,
    cmd_tx: Sender<SessionCmd>,
    cmd_rx: Receiver<SessionCmd>,
    event_tx: Sender<EngineEvent>,
    event_rx: Receiver<EngineEvent>,
    notifications: NotificationDrain,
) -> SessionHandle

Spawn against pre-created command and event channels (see session_channel/event_channel) — what a caller needs when a session-scoped tool’s sink (ask_user) must hold live senders to both before the actor exists.