Module flow 

Per-flow UDP state machine (sans-io).

A UdpFlow is the per-admitted-flow half of the two-level split. It owns the three-knob teardown counters (responses / requests / idle), the idle and lifetime deadlines, PPv2-first-datagram bookkeeping, the real (pre-NAT) client address, the chosen backend, and the forward/return decisions. It carries a timer_gen generation token so a stale wheel expiry cannot close a flow that has since seen traffic.

No socket, no clock, no rand: every time-dependent method takes now: Instant. The manager owns the slab; this type is the slot payload.

Structs

UdpFlow

Per-admitted-flow state. Slab slot payload owned by the manager.

Enums

CloseReason

Why a flow reached teardown. Surfaces in the access log on close.

FlowPhase

The lifecycle of a flow w.r.t. its backend. A flow is admitted in AwaitingBackend, transitions to Established once the shell resolves and opens an upstream, and is reaped on teardown.