Enum LeafPermit 

pub enum LeafPermit {
    OpenFile(OpenFileGuard),
    PendingMeta(PendingMetaGuard),
}

A pre-acquired leaf permit, type-erased over the two distinct backpressure pools so a single caller (the traversal driver) can hold either uniformly and drop it in exactly one place before recursing into a directory.

The two pools must stay distinct: throttle::OpenFileGuard gates open file descriptors while throttle::PendingMetaGuard gates in-flight metadata-only tasks. They are sized independently so a path that composes the two operations (e.g. copy_file → rm when overwriting a directory destination) cannot self-deadlock against a saturated open-files pool. This enum unifies only the lifecycle, never the pools themselves.

Neither guard is Clone; dropping a LeafPermit releases exactly the underlying permit it wraps. The driver drops it before descending so a directory entry never holds a leaf permit across its recursive walk — the single home for the invariant that previously lived at 4/7/1/1 per-tool branch sites and shipped as a deadlock when a single-site tool forgot it.

Variants

OpenFile(OpenFileGuard)

A permit from the open-files pool.

PendingMeta(PendingMetaGuard)

A permit from the pending-metadata pool.