wf start: refuse worktree of another repo; .wf-home not stray

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JEAjUkQRrCYX5MZhWxdtj2

2 files changed, 39 insertions, 1 deletions

diff --git a/tests/test_split.py b/tests/test_split.py
index 934bf6f..9d19308 100644
--- a/tests/test_split.py
+++ b/tests/test_split.py
@@ -91,6 +91,26 @@ class StartSplitTest(SplitCli):
         self.assertIn(f"cd {wt} && (make test) && ", out)
         self.assertFalse((self.root / ".worktrees").exists())                  # nothing in the private repo
 
+    def test_start_refuses_private_repo_worktree(self):
+        wt = self.root / ".worktrees" / "slow"
+        git(self.root, "worktree", "add", "-q", str(wt), "-b", "slow/old")
+        code, out, err = self.wf("start", "t-three", "--worktree", str(wt), "--branch", "slow/t-three",
+                                 project=False, env=IDENT)
+        self.assertNotEqual(code, 0)
+        self.assertIn("is not a worktree of", err)
+        self.assertFalse((wt / ".wf-home").exists())
+        self.assertEqual(subprocess.run(["git", "branch", "--show-current"], cwd=wt, capture_output=True,
+                                        text=True).stdout.strip(), "slow/old")             # not switched
+        self.assertIn("- **t-three** [P2] (<1h): Third", (self.root / "TASKS.md").read_text())   # no progress
+
+    def test_start_reuses_existing_code_worktree(self):
+        wt = self.code / ".worktrees" / "slow"
+        git(self.code, "worktree", "add", "-q", str(wt), "-b", "slow/old")
+        code, out, err = self.wf("start", "t-three", "--worktree", str(wt), "--branch", "slow/t-three",
+                                 project=False, env=IDENT)
+        self.assertEqual(code, 0, out + err)
+        self.assertEqual((wt / ".wf-home").read_text(), f"{self.root}\n")
+
     def test_setup_in_code_worktree(self):
         wt = self.add_wt()
         code, out, err = self.wf("setup", project=False, cwd=wt)
@@ -152,6 +172,16 @@ class FinishSplitTest(SplitCli):
         self.assertEqual(subprocess.run(["git", "branch", "--list", "sonnet/t-three"], cwd=self.code,
                                         capture_output=True, text=True).stdout, "")
 
+    def test_unignored_wf_home_does_not_block(self):
+        (self.code / ".gitignore").write_text(".worktrees/\n")
+        git(self.code, "commit", "-qam", "no wf-home ignore")
+        git(self.wt, "rebase", "-q", "master")
+        (self.wt / "code.txt").write_text("x\n")
+        code, out, err = self.finish("t-three", "-m", "ok", "--commit", "impl", "code.txt")
+        self.assertEqual(code, 0, out + err)
+        self.assertNotIn(".wf-home", subprocess.run(["git", "show", "--stat", "master"], cwd=self.code,
+                                                    capture_output=True, text=True).stdout)
+
     def test_stray_code_file_refused_task_open(self):
         (self.wt / "code.txt").write_text("x\n")
         (self.wt / "stray.txt").write_text("s\n")
diff --git a/wf.py b/wf.py
index 7b5ae12..dda4914 100755
--- a/wf.py
+++ b/wf.py
@@ -1231,7 +1231,7 @@ def cmd_merge(args) -> int:
     bmain = config.git_top(cfg.root) or main        # books repo: the private repo of a split project, else main
     private = [str(Path(x).resolve().relative_to(bmain.resolve())) for x in getattr(args, "private", None) or []]
     files = [str(f.relative_to(bmain)) for f in (cfg.tasks, cfg.archive)] + private
-    if git_run(top, "status", "--porcelain", "-uall").stdout.strip():
+    if _dirty_outside(top, []):
         raise Failure("worktree has uncommitted changes: commit them first")
     had = unmerged_count(top, master)
     if not branch and not had:
@@ -1326,6 +1326,8 @@ def _dirty_outside(top: Path, keep: list[Path]) -> list[str]:
     for line in git_run(top, "status", "--porcelain", "-uall").stdout.splitlines():
         rel = line[3:].split(" -> ")[-1].strip('"').rstrip("/")
         path = (top / rel).resolve()
+        if rel == config.WF_HOME:       # wf start's pointer in a code worktree, never committed
+            continue
         if not any(path == k or k in path.parents for k in keep):
             stray.append(rel)
     return stray
@@ -1531,6 +1533,12 @@ def cmd_start(args) -> int:
             git_ok(repo, "worktree", "add", "-q", str(wt), "-b", b, master)
             how = f"new, branch {b} from {master}"
     else:
+        own = git_run(wt, "rev-parse", "--path-format=absolute", "--git-common-dir").stdout.strip()
+        want = git_run(repo, "rev-parse", "--path-format=absolute", "--git-common-dir").stdout.strip()
+        if not own or Path(own).resolve() != Path(want).resolve():
+            raise Failure(f"{shown} is not a worktree of {repo}"
+                          + (f" (it belongs to {Path(own).resolve().parent})" if own else "")
+                          + f": pass a worktree path of {repo} (e.g. {repo}/.worktrees/<lane>)")
         dirty = git_run(wt, "status", "--porcelain").stdout.rstrip("\n")
         cur = config.git_branch(Path(git_run(wt, "rev-parse", "--absolute-git-dir").stdout.strip()))
         if dirty and not args.recovery: