Module loop_sweep 

Call-driven sweep for closed-loop topologies. LoopSweep — call-driven dispatch for LineKind::Loop groups.

On a one-way closed loop, “dispatch” reduces to a label: the systems::dispatch phase already kickstarts an Idle Loop car onto its forward-next stop and excludes Loop cars from the Hungarian idle pool, and the door FSM hands the car straight from DoorClosing back to MovingToStop(next) without ever passing through Stopped. The loading phase boards every eligible rider regardless of the linear up/down lamps, so a Loop car serves every waiter at every served stop on every lap.

That continuous-patrol behaviour is the LoopSweep contract from docs/plans/loop-lines-v1.md. This struct exists so that:

• Loop groups have a typed default that round-trips through snapshots and config files via BuiltinStrategy::LoopSweep instead of silently inheriting BuiltinStrategy::Scan — which would replay any restored sim with the wrong identity.
• The construction-time validation can name the only strategy a Loop group is allowed to carry, rejecting Linear-only strategies loud rather than silently misbehaving.

All DispatchStrategy hooks fall back to defaults: Loop cars never reach the Hungarian, so rank is unreachable in practice, and there is no per-car or per-pass scratch that needs to round-trip — the whole struct is unit-shaped.

Future Loop-aware behaviour (skip-empty-stops, headway-driven hold recovery) will land in successors (LoopSchedule).

Structs

LoopSweepDispatch

Dispatch strategy for LineKind::Loop groups.