diff --git a/.delphi/manifest.yml b/.delphi/manifest.yml
index fb1aa03..484f83d 100644
--- a/.delphi/manifest.yml
+++ b/.delphi/manifest.yml
@@ -6,7 +6,7 @@
 #   MINOR  something new that existing clones need nothing for
 #   MAJOR  clones need cleanup (MINOR while 0.x): add .delphi/migrations/<version>-<slug>.sh, which
 #          setup.sh runs once per workspace in each clone (rules in Delphi's CLAUDE.md)
-version: 2.1.0
+version: 2.1.1
 files:                        # repo-relative paths; a trailing / means everything under it
   - .delphi/manifest.yml
   - .delphi/.gitattributes
diff --git a/.delphi/new-worktree.sh b/.delphi/new-worktree.sh
index 6e53461..ded2452 100755
--- a/.delphi/new-worktree.sh
+++ b/.delphi/new-worktree.sh
@@ -2,7 +2,8 @@
 # .delphi/new-worktree.sh <repo> <branch> [<base>]: create or reuse worktrees/<repo>/<branch> from
 # the bare store .delphi/setup.sh made at worktrees/<repo>/.bare (never the clone at repos/<repo>), and
 # print its path. An existing branch (local or on origin) is checked out; a new one starts from <base>
-# (default: origin's default branch). Runs on bash 3.2 and Git Bash.
+# (default: origin's default branch; a <base> only on origin is used as origin/<base>), and the script
+# fails unless the worktree ends up on <branch>. Runs on bash 3.2 and Git Bash.
 set -euo pipefail
 # shellcheck source-path=SCRIPTDIR source=paths.sh
 . "$(dirname "$0")/paths.sh"
@@ -18,7 +19,13 @@ elif g rev-parse -q --verify "refs/heads/$branch" >/dev/null; then
   g worktree add -q "$dest" "$branch"
 elif g rev-parse -q --verify "refs/remotes/origin/$branch" >/dev/null; then
   g worktree add -q --track -b "$branch" "$dest" "origin/$branch"
-else
+else # a <base> only on origin goes as origin/<base>: given the bare name, Git 2.43 checks out <base>, not -b
+  if ! g rev-parse -q --verify "$base^{commit}" >/dev/null && g rev-parse -q --verify "refs/remotes/origin/$base" >/dev/null; then
+    base=origin/$base
+  fi
   g worktree add -q --no-track -b "$branch" "$dest" "$base"
 fi
+on=$(git -C "$dest" branch --show-current)
+[ "$on" = "$branch" ] || { echo "new-worktree: worktrees/$repo/$branch is on '${on:-a detached HEAD}', not '$branch';" \
+  "remove it (git -C worktrees/$repo/.bare worktree remove ../$branch) and rerun" >&2 && exit 1; }
 echo "$dest"
diff --git a/.delphi/versions b/.delphi/versions
index 1c95e06..e21026d 100644
--- a/.delphi/versions
+++ b/.delphi/versions
@@ -19,3 +19,4 @@
 1.2.0 d139aaf9f4a5 worktrees come from their own bare store, worktrees/<name>/.bare, separate from the plain clone at repos/<name>; setup.sh makes the store and the default-branch worktree again; an older bare store at repos/<name> is left as it is
 2.0.0 750acf945979 a bare repos/<name> from before 1.1.0 becomes the worktree store, worktrees/<name>/.bare, with its worktrees, and repos/<name> is cloned normally (migration; skipped with a message if it has no origin or work not on origin)
 2.1.0 84b00128fc22 add a harness-independent per-command workspace bootstrap for Codex
+2.1.1 66714104d7a3 new-worktree.sh passes a <base> only on origin as origin/<base> (Git 2.43 checked out <base> instead of -b) and fails unless the worktree is on <branch> (#85)
diff --git a/tests/e2e.sh b/tests/e2e.sh
index fd9d04f..f2751e4 100644
--- a/tests/e2e.sh
+++ b/tests/e2e.sh
@@ -1073,11 +1073,18 @@ nw code feat >/dev/null && [ "$(git -C "$w/worktrees/code/feat" rev-parse HEAD)"
 [ "$(git -C "$w/worktrees/code/feat" rev-parse --abbrev-ref '@{u}')" = origin/feat ] || fail "existing branch not tracking origin"
 nw code 2-dev origin/develop >/dev/null && [ "$(git -C "$w/worktrees/code/2-dev" rev-parse HEAD)" = "$(git -C "$t/code" rev-parse develop)" ] ||
   fail "<base> ignored"
+! git -C "$w/worktrees/code/.bare" rev-parse -q --verify refs/heads/develop >/dev/null || fail "store already has a local develop"
+nw code 3-dev develop >/dev/null && [ "$(git -C "$w/worktrees/code/3-dev" branch --show-current)" = 3-dev ] &&
+  [ "$(git -C "$w/worktrees/code/3-dev" rev-parse HEAD)" = "$(git -C "$t/code" rev-parse develop)" ] || fail "<base> only on origin: not on the new branch"
+! git -C "$w/worktrees/code/.bare" rev-parse -q --verify refs/heads/develop >/dev/null || fail "<base> only on origin: left a local develop"
+git -C "$w/worktrees/code/.bare" worktree add -q --detach "$w/worktrees/code/4-off" origin/develop
+! nw code 4-off >/dev/null 2>"$t/err" || fail "worktree off its branch not refused"
+grep -q "is on 'a detached HEAD', not '4-off'" "$t/err" || fail "worktree off its branch refusal unexplained: $(cat "$t/err")"
 [ "$(nw code feat)" = "$w/worktrees/code/feat" ] || fail "rerun did not reuse"
 [ "$(git -C "$w/worktrees/code/$def" branch --show-current)" = "$def" ] || fail "default worktree left its branch"
 { [ "$(git -C "$w/repos/code" branch --show-current)" = "$def" ] && [ "$(git -C "$w/repos/code" worktree list | wc -l | tr -d " ")" = 1 ] &&
   ! git -C "$w/repos/code" rev-parse -q --verify refs/heads/1-new >/dev/null; } || fail "new-worktree touched the clone at repos/code"
-ok "new-worktree.sh makes new branches from the default or <base>, checks out existing ones, reuses on rerun, never touching repos/<repo>"
+ok "new-worktree.sh makes new branches from the default or <base> (local or only on origin), checks out existing ones, reuses on rerun, refuses a worktree off its branch, never touching repos/<repo>"
 # skill scripts read the workspace from $DELPHI_ROOT (the session hook evals paths.sh's export line) and every folder from paths.sh
 (. "$w/.delphi/paths.sh" && [ "$DELPHI_ROOT" = "$w" ] && [ "$DELPHI_REPOS" = "$w/repos" ] &&
   [ "$DELPHI_WORKTREES" = "$w/worktrees" ] && [ "$DELPHI_REFERENCES" = "$w/references" ] && [ "$DELPHI_WORKSPACES" = "$w/workspaces" ]) ||