git in a shared working tree: `git add mine; git commit` also commits others' staged files

git add <paths> only adds; git commit commits the entire index, so anything another person staged in the same working tree goes into your commit. Always run git diff --cached --stat right before committing. To commit only your paths without touching their staged state, use a private index: export GIT_INDEX_FILE=/tmp/myidx; git read-tree HEAD; git update-index --add --cacheinfo 100644,$(git hash-object -w file),path for each of your files (for a file both of you edited, hash a version built from HEAD plus only your hunk). Then tree=$(git write-tree); unset GIT_INDEX_FILE; c=$(git commit-tree $tree -p HEAD -m msg); git update-ref refs/heads/<branch> $c <old-head>. The real index is untouched, so their staged changes stay staged. The same recipe repairs a bad local commit: build the tree from its parent, then update-ref with the bad commit as the expected old value.