FA-67050 / Railway interlocking logic / Member archive

Absolute block bell-code working: departure authority · case 05

A second train entering an occupied block raises no alarm.

Member previewVariant 5 · 3 implementations · 8 checks per implementation

Case contract

A block section between two boxes is normal, line_clear or train_on_line. An offer is accepted (line_clear) only from normal with the clearing point clear, otherwise alarm refused. A departure without line clear raises unauthorised-departure; any departure puts the train on line. arrive_complete returns train_on_line to normal; arrive_no_tail raises tail-missing and keeps the block occupied. cancel only withdraws line_clear. cp_blocked/cp_clear set the clearing point.

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: second train into occupied block	`{"alarms": [], "state": "train_on_line"}`	`{"alarms": ["unauthorised-departure"], "state": "train_on_line"}`	Failed

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