The fallback for failed cherry-picks used `git diff HEAD $sha` which
computes the diff between the linearize branch and the commit's full
tree. This captures ALL tree differences, not just the changes the
commit introduced — causing unrelated file deletions.
Fix: diff from the commit's own parent (`${sha}^` for regular commits,
`${sha}^1` for merge commits). Also detect and skip empty merges
(where cherry-pick -m 1 produces nothing because the changes were
already applied by a prior cherry-pick).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
SBPro
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