[Bug]: A new worktree fails with path_already_exists when its folder is left over from an earlier one #35108

# Run in an empty folder on Linux with git and vp (Vite+) installed.
# The bug needs a NAMED branch (--branch feature/foo) that does not exist yet.
# The web composer's "New worktree" never hits it: it always picks a random branch and folder name.
WORK=$PWD
export GIT_AUTHOR_NAME=Sample [email protected] GIT_COMMITTER_NAME=Sample [email protected]
SRC=${T3_SRC:-$WORK/t3code}
if [ ! -d "$SRC" ]; then
  git clone https://github.com/pingdotgg/t3code.git "$SRC"
  git -C "$SRC" checkout b68aedfdb71534bfdfbe55771ef2e686742faa8e
  (cd "$SRC" && vp i)
fi
HOME_DIR=$WORK/t3-home
t3() { (cd "$SRC/apps/server" && vp env exec --node 26.12.1 node src/bin.ts "$@" --base-dir "$HOME_DIR"); }

# 1. A repository with one commit.
git init -b main "$WORK/sample-app"
echo "# sample app" > "$WORK/sample-app/README.md"
git -C "$WORK/sample-app" add README.md
git -C "$WORK/sample-app" commit -m "Initial commit"

# 2. A dev server from source with an empty data folder (it includes the free "Replay (dev)" provider).
(cd "$SRC" && exec vp run dev --home-dir "$HOME_DIR" --no-seed) > "$WORK/server.log" 2>&1 &
until grep -q pairingUrl "$WORK/server.log"; do sleep 1; done

# 3. Add the project, then start a thread in a new worktree on the named branch feature/foo.
t3 project add "$WORK/sample-app"
t3 thread start "$WORK/sample-app" "First run" --worktree main --branch feature/foo --provider devReplay --model showcase --wait

# 4. Print the worktree folder, remove the worktree and its branch, and leave a file of mine in that folder.
dir=$(git -C "$WORK/sample-app" worktree list --porcelain | awk '/^worktree /{p=$2} /^branch refs\/heads\/feature\/foo$/{print p}')
echo "$dir"
git -C "$WORK/sample-app" worktree remove --force "$dir"
git -C "$WORK/sample-app" branch -D feature/foo
mkdir "$dir"
echo "my notes" > "$dir/notes.txt"

# 5. Start a thread for the same branch again, then show the result.
t3 thread start "$WORK/sample-app" "Second run" --worktree main --branch feature/foo --provider devReplay --model showcase --wait
git -C "$WORK/sample-app" worktree list
ls -A "$dir"

dir=$(git -C "$WORK/sample-app" worktree list --porcelain | awk '/^worktree /{p=$2} /^branch refs\/heads\/feature\/foo$/{print p}')
echo "$dir"
/tmp/repro/t3-home/worktrees/sample-app/feature-foo-8799fc65b79a025b
git -C "$WORK/sample-app" worktree remove --force "$dir"
git -C "$WORK/sample-app" branch -D feature/foo
Deleted branch feature/foo (was 46bd545).
mkdir "$dir"
echo "my notes" > "$dir/notes.txt"
# 5. Start a thread for the same branch again, then show the result.
t3 thread start "$WORK/sample-app" "Second run" --worktree main --branch feature/foo --provider devReplay --model showcase --wait
Thread mcp:11a18202-1da4-4675-a0d3-226750318000
Thread mcp:11a18202-1da4-4675-a0d3-226750318000 stopped with status failed: Workspace preparation failed during provision worktree: Git command failed in GitVcsDriver.createWorktree (/tmp/repro/sample-app): git worktree add failed (path_already_exists)
git -C "$WORK/sample-app" worktree list
/tmp/repro/sample-app 46bd545 [main]
ls -A "$dir"
notes.txt