FA-67469 / Elevator dispatch scheduling / Member archive

Floor label and index mapping: index range guard · case 04

A negative index returns a label from the top of the building.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

Physical indices 0..floors-1 are labelled bottom-up: basements Bk..B1, then G, then M if there is a mezzanine, then 1, 2, 3 ... skipping 13 when skip13. label:i returns the label of index i (None outside the range); index:L returns the index of label L (case-insensitive) or None.

Why this case matters

Lift group controllers make these decisions many times per minute; a wrong answer strands passengers, wastes trips or overrides a safety rule.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression: negative index	`["7", "B1"]`	`[null, "B1"]`	Failed

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