FA-82360 / Chess move legality / Member archive

Mistyped knight offset produces a pawn-like step · case 05

A knight is offered the square two ranks straight below it.

Member previewVariant 5 · 3 implementations · 8 checks per implementation

Case contract

Input: {"board": {square: piece}, "from": square of a knight}. Squares are indexed 0..63 with a1=0, h1=7, a8=56. Return the sorted list of pseudo-legal knight destinations: on the board, not wrapping across the a/h file edge, and not occupied by a piece of the knight's colour.

Why this case matters

Move validators gate every move in engines, servers and arbiters; accepting an illegal move or rejecting a legal one corrupts the game record.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
h-file knight	`["f2", "f4", "g5", "h1"]`	`["f2", "f4", "g1", "g5"]`	Failed

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This record includes three runnable implementations, regression fixtures, execution results, and source hashes.

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