FA-67285 / Railway interlocking logic / Member archive

Flank protection selection: indirect protection availability · case 05

A route is protected by a flank signal that cannot actually be held.

Member previewVariant 5 · 3 implementations · 8 checks per implementation

Case contract

For each route point (sorted) in its lie, the flank table (key point+lie) lists flank points with the protecting lie and an optional flank signal. A flank point is set to its protecting lie if it is free, locked in that lie by another route, or already demanded in that lie by this route; if it is unavailable, its flank signal is held at danger when the signal exists and is holdable; otherwise the route is refused (refused:<flank point>, nothing set or held). Held signals are returned sorted and unique.

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: flank signal not holdable	`{"held_signals": ["S21"], "result": "protected", "set_points": {}}`	`{"held_signals": [], "result": "refused:P7", "set_points": {}}`	Failed

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