Enum NextStep 

pub enum NextStep {
    Dispatch(Unit),
    Drained,
    Pause {
        policy: String,
        detail: String,
    },
}

The richer return type for Queue::next_step(). Used by policy-aware queues (MegawalkQueue) to signal a walk-level pause without returning an error.

• Dispatch(Unit): there is work to do; dispatch this unit.
• Drained: the queue is empty; the walk may complete with NoWork.
• Pause{policy, detail}: walk policy says stop; run_loop maps this to walk_paused + loop_terminated{reason: NoProgress}.

Queues that do not implement walk policy (TargetQueue) return only Dispatch / Drained (i.e., they translate their Option to these two).

Variants

Dispatch(Unit)

There is a unit ready to dispatch.

Drained

The queue is empty; no more work.

Pause

Walk policy requests a pause.

Fields

policy: String

Short tag: “consecutive_failures” | “p0_failed”.

detail: String

Human-readable detail (unit IDs involved, streak count, etc.).