When checking known patches to detect zombie conflicts, the "known" list was computed on the neighbouring changes (when producing patches), whereas the checks were performed on the edges.
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// When reintroducing a deleted flag, check whether
// the re-introduction patch knows about the alive
// edges around the target.
// When reintroducing an edge that was deleted,
// check whether the re-introduction patch knows
// about the alive edges around the target.