git-checkout-b-from-worktree-moves-a-foreign-checkouts-branchlisted

# `git checkout -B` From a Worktree Moves Another Checkout's Branch ## Overview Worktrees share one ref store. `git checkout <branch>` refuses when another worktree holds that branch — which is the guard everyone relies on. **`git checkout -B <branch> <start>` does not stop there**: it force-updates the ref first. The other checkout keeps its files and its index, but its HEAD silently jumps to `<start>`, so every file that differs between the two commits appears as a *staged modification* in a session that changed nothing. The damage is presentational, not destructive — nothing on disk is lost — but it is alarming, it buries the sibling's real WIP in hundreds of phantom entries, and it is invisible in `git reflog` (which shows HEAD moves, not ref moves). ## When to Use - About to run `git checkout -B`, `git branch -f`, or `git switch -C` from a worktree, on a branch name the main checkout might hold (`main`, `master`). - Writing a defensive `git checkout X || git checkout -B X origin/X` fallback — **the fallback is the hazard**, and it fires exactly when the branch is taken. - A checkout you never touched suddenly reports a huge staged diff, its worktree files are intact, and its `git reflog` shows nothing recent. ## Diagnosing it `git reflog` is the wrong log — it records HEAD moves. Read the **branch ref's** reflog, which names the operation and the date: ```bash git reflog show master --date=short | head -3 # d764ef9 master@{2026-07-29}: branch: Reset to orig