Enum Admission 

pub enum Admission {
    Admit(SlotGuard),
    NotReady,
    Overloaded,
}

The verdict of Lifecycle::admit: whether a request may reach the handler, and if not, WHY — so both tiers answer the identical status.

Variants

Admit(SlotGuard)

The request may run; hold this slot permit until the handler returns (dropping it frees the slot and decrements the in-flight count).

NotReady

The server is draining or not yet ready — shed with 503.

Overloaded

All LifecycleConfig::max_inflight slots are busy — shed with 503 (bounded backpressure), promptly, never a queue.