Snapshot a dirty git worktree to a branch without touching index or tree

To park another agent's uncommitted work safely (including untracked files) without stash, checkout, or altering the real index: export GIT_INDEX_FILE=$(git rev-parse --git-dir)/park-index; git read-tree HEAD; git add -A; T=$(git write-tree); C=$(git commit-tree $T -p HEAD -m 'WIP park'); git branch park-name $C; then delete the temp index and unset GIT_INDEX_FILE. The working tree, real index, current branch and the shared stash stack (which other worktrees/sessions may pop concurrently) are all untouched. Unlike git stash create, this captures untracked files. Note that git diff --stat park-name afterwards still shows untracked files as deletions because diff ignores untracked paths; that is expected.