FA-67177 / Railway interlocking logic / Member archive

Signal replacement and stick control: replacement stick latch · case 02

A signal re-clears behind a train for a following train on the same route setting.

Member previewVariant 2 · 3 implementations · 8 checks per implementation

Case contract

Each step gives [section beyond occupied, route set, approach occupied]. An auto signal behaves as permanently routed. A signal shows danger whenever the section beyond is occupied; a signal that was clear when a train occupies that section latches a stick that keeps it at danger until the route is set afresh (off then on); auto signals drop the stick every step. Otherwise it clears when routed, not stuck, and for approach-released signals only with the approach occupied. Output the state per step.

Why this case matters

Interlocking logic decides whether trains may be given authority; a wrong decision at this point either grants unsafe movements or strands traffic.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression: approach-released signal replaced by train	`["clear", "danger", "clear"]`	`["clear", "danger", "danger"]`	Failed

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