FA-75634 / Text diff and three-way merge / Member archive

Merge base selection: only one of several merge bases is returned · case 04

Criss-cross merges pick an arbitrary base and can report spurious conflicts or silently revert changes.

Member previewVariant 4 · 3 implementations · 10 checks per implementation

Case contract

Given a commit graph (commit -> parent list) and two commits, ancestors include the commit itself and all commits reachable through any parent. The merge bases are the common ancestors that are not ancestors of another common ancestor. Return them sorted.

Why this case matters

A three-way merge is only as good as its base; criss-cross histories legitimately have several best common ancestors.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
criss-cross has two merge bases	`["X1"]`	`["X1", "Y1"]`	Failed

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