Function drain_worker_handles 

pub async fn drain_worker_handles(
    handles: Vec<WorkerHandle>,
    timeout: Duration,
) -> bool

Join the pipeline worker handles so in-flight work drains before the runtime is torn down on shutdown (D7). Bounded by timeout; if it elapses, remaining work is abandoned (at-least-once redelivery is the backstop). Returns true if the drain completed within the window, false on timeout.

WorkerHandle::Apalis handles (if any) are dropped — the apalis Monitor shuts down via its own signal handling.