FA-67104 / Railway interlocking logic / Member archive

Movement authority end computation: margin application · case 04

A length-capped authority is shortened by the safety margin.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

Sections have lengths and states locked, occupied or unlocked; the train front is offset_m into section train_sec (which it occupies itself). Scan the following sections; the end of authority is the start of the first section that is not locked (reason = its state) or the end of the last section (end-of-route). If that exceeds max_ma_m ahead of the train front, the authority is cut to front + max_ma_m (reason max-length). The margin is subtracted from the end except for a max-length cut.

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: length cap from the front	`{"eoa_m": 975, "reason": "max-length"}`	`{"eoa_m": 1000, "reason": "max-length"}`	Failed

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