fix: count worktree branches in git extension numbering

extensions/git/scripts/bash/create-new-feature-branch.sh

@@ -127,7 +127,7 @@ get_highest_from_specs() {
 
 # Function to get highest number from git branches
 get_highest_from_branches() {
-    git branch -a 2>/dev/null | sed 's/^[* ]*//; s|^remotes/[^/]*/||' | _extract_highest_number
+    git branch -a 2>/dev/null | sed -E 's/^[+*][[:space:]]+//; s/^[[:space:]]+//; s|^remotes/[^/]*/||' | _extract_highest_number
 }
 
 # Extract the highest sequential feature number from a list of ref names (one per line).

extensions/git/scripts/powershell/create-new-feature-branch.ps1

@@ -88,7 +88,7 @@ function Get-HighestNumberFromBranches {
         $branches = git branch -a 2>$null
         if ($LASTEXITCODE -eq 0 -and $branches) {
             $cleanNames = $branches | ForEach-Object {
-                $_.Trim() -replace '^\*?\s+', '' -replace '^remotes/[^/]+/', ''
+                $_.Trim() -replace '^[+*]?\s+', '' -replace '^remotes/[^/]+/', ''
             }
             return Get-HighestNumberFromNames -Names $cleanNames
         }

tests/extensions/git/test_git_extension.py

@@ -89,6 +89,17 @@ def _write_config(project: Path, content: str) -> Path:
     return config_path
 
 
+def _add_sibling_worktree(project: Path, path: Path, branch: str) -> None:
+    """Add a sibling worktree so `git branch -a` marks it with `+`."""
+    subprocess.run(
+        ["git", "worktree", "add", "-q", "-b", branch, str(path), "HEAD"],
+        cwd=project,
+        check=True,
+        capture_output=True,
+        text=True,
+    )
+
+
 # Git identity env vars for CI runners without global git config
 _GIT_ENV = {
     "GIT_AUTHOR_NAME": "Test User",
@@ -312,6 +323,40 @@ def test_increments_from_existing_specs(self, tmp_path: Path):
         data = json.loads(result.stdout)
         assert data["FEATURE_NUM"] == "003"
 
+    def test_dry_run_counts_branches_checked_out_in_worktrees(self, tmp_path: Path):
+        """Branches checked out in sibling worktrees still reserve their prefix."""
+        project = _setup_project(tmp_path / "project")
+        _add_sibling_worktree(project, tmp_path / "sibling-worktree", "007-worktree-feature")
+
+        result = _run_bash(
+            "create-new-feature-branch.sh", project,
+            "--json", "--dry-run", "--short-name", "next", "Next feature",
+        )
+
+        assert result.returncode == 0, result.stderr
+        data = json.loads(result.stdout)
+        assert data["BRANCH_NAME"] == "008-next"
+        assert data["FEATURE_NUM"] == "008"
+
+    def test_dry_run_preserves_literal_plus_branch_prefix(self, tmp_path: Path):
+        """A literal leading plus in a branch name is not a git worktree marker."""
+        project = _setup_project(tmp_path)
+        subprocess.run(
+            ["git", "branch", "+007-plus-prefix"],
+            cwd=project,
+            check=True,
+        )
+
+        result = _run_bash(
+            "create-new-feature-branch.sh", project,
+            "--json", "--dry-run", "--short-name", "next", "Next feature",
+        )
+
+        assert result.returncode == 0, result.stderr
+        data = json.loads(result.stdout)
+        assert data["BRANCH_NAME"] == "001-next"
+        assert data["FEATURE_NUM"] == "001"
+
     def test_no_git_graceful_degradation(self, tmp_path: Path):
         """create-new-feature-branch.sh works without git (outputs branch name, skips branch creation)."""
         project = _setup_project(tmp_path, git=False)
@@ -351,6 +396,21 @@ def test_creates_branch_sequential(self, tmp_path: Path):
         data = json.loads(result.stdout)
         assert data["BRANCH_NAME"] == "001-user-auth"
 
+    def test_dry_run_counts_branches_checked_out_in_worktrees(self, tmp_path: Path):
+        """Branches checked out in sibling worktrees still reserve their prefix."""
+        project = _setup_project(tmp_path / "project")
+        _add_sibling_worktree(project, tmp_path / "sibling-worktree", "007-worktree-feature")
+
+        result = _run_pwsh(
+            "create-new-feature-branch.ps1", project,
+            "-Json", "-DryRun", "-ShortName", "next", "Next feature",
+        )
+
+        assert result.returncode == 0, result.stderr
+        data = json.loads(result.stdout)
+        assert data["BRANCH_NAME"] == "008-next"
+        assert data["FEATURE_NUM"] == "008"
+
     def test_creates_branch_timestamp(self, tmp_path: Path):
         """Extension create-new-feature-branch.ps1 creates timestamp branch."""
         project = _setup_project(tmp_path)