fix(powershell): stop create-new-feature crashing on a non-Latin description (#4138)

Get-BranchName's fallback assumed the pipeline yields at least one element:

    $fallbackWords = ($result -split '-') | Where-Object { $_ } | ...
    return [string]::Join('-', $fallbackWords)

ConvertTo-CleanBranchName blanks every non-[a-z0-9] character, so a
description written in any non-Latin script leaves nothing for the pipeline
to emit. It yields $null, [string]::Join throws ArgumentNullException, and
$ErrorActionPreference = 'Stop' makes that terminating — the script dies
with a .NET stack trace, empty stdout, exit 1.

Measured with all three twins installed in one project:

  desc='добавить авторизацию'
    bash rc=0 BRANCH_NAME='001-'
    py   rc=0 BRANCH_NAME='001-'
    ps   rc=1 Exception calling "Join" ...

Identical for 添加用户认证 and '!!! ??? ***'. This hits every PowerShell
user who phrases a feature in their own language.

Wrap the pipeline in @() so it stays an array; Join on an empty array
returns "", matching the twins. Verified the normal case is unchanged
('a-to-the-of' -> 'a-to-the', 'add user authentication' ->
'001-user-authentication'), and the file stays ASCII-only (0 non-ASCII
bytes) for tests/test_ps1_encoding.py.

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: jawwad-ali

scripts/powershell/create-new-feature.ps1

@@ -162,7 +162,14 @@ function Get-BranchName {
     } else {
         # Fallback to original logic if no meaningful words found
         $result = ConvertTo-CleanBranchName -Name $Description
-        $fallbackWords = ($result -split '-') | Where-Object { $_ } | Select-Object -First 3
+        # @() keeps this an array. ConvertTo-CleanBranchName blanks every
+        # non-[a-z0-9] character, so a description written in a non-Latin script
+        # (or made only of punctuation) leaves nothing for the pipeline to
+        # emit -- it yields $null, and [string]::Join on $null throws
+        # ArgumentNullException. With $ErrorActionPreference = 'Stop' that is
+        # terminating, so the script died with a .NET stack trace and exit 1
+        # where the bash and Python twins both return an empty suffix.
+        $fallbackWords = @(($result -split '-') | Where-Object { $_ } | Select-Object -First 3)
         return [string]::Join('-', $fallbackWords)
     }
 }

tests/test_create_new_feature_python_parity.py

@@ -1065,3 +1065,56 @@ def test_all_variants_corrected_prefix_skips_timestamp_collision(repo: Path) ->
     assert json_stdout(py)["FEATURE_NUM"] == "20260320"
     for result in (bash, ps, py):
         assert "using 20260320 instead" in result.stderr
+
+
+@pytest.mark.skipif(not HAS_POWERSHELL, reason="no PowerShell available")
+@pytest.mark.parametrize(
+    "description",
+    ["!!! ??? ***", "добавить", "添加用户"],
+    ids=["punctuation_only", "cyrillic", "han"],
+)
+def test_powershell_survives_description_with_no_ascii_words(
+    tmp_path: Path, description: str
+):
+    """A description with no [a-z0-9] characters must not crash the PS twin.
+
+    ``ConvertTo-CleanBranchName`` blanks every non-ASCII character, so the
+    fallback pipeline yields nothing and ``[string]::Join`` received ``$null``
+    — an ArgumentNullException, made terminating by
+    ``$ErrorActionPreference = 'Stop'``. The script died with a .NET stack
+    trace and exit 1 where the bash and Python twins both return an empty
+    suffix. This fires for any feature phrased in a non-Latin script.
+    """
+    repo = _setup_repo(tmp_path)
+
+    ps = run(ps_cmd(repo, SCRIPT, "-Json", "-DryRun", description), repo)
+
+    assert ps.returncode == 0, ps.stderr
+    assert "ArgumentNullException" not in ps.stderr
+    assert "Join" not in ps.stderr
+    assert json_stdout(ps)["BRANCH_NAME"] == "001-"
+
+
+@requires_bash
+@pytest.mark.skipif(not HAS_POWERSHELL, reason="no PowerShell available")
+def test_no_ascii_word_description_matches_across_twins(tmp_path: Path):
+    """All three twins agree on the branch name for such a description."""
+    description = "добавить"
+
+    bash_repo = _setup_repo(tmp_path, "b")
+    py_repo = _setup_repo(tmp_path, "p")
+    ps_repo = _setup_repo(tmp_path, "s")
+
+    bash = run(bash_cmd(bash_repo, SCRIPT, "--json", "--dry-run", description), bash_repo)
+    py = run(py_cmd(py_repo, SCRIPT, "--json", "--dry-run", description), py_repo)
+    ps = run(ps_cmd(ps_repo, SCRIPT, "-Json", "-DryRun", description), ps_repo)
+
+    assert bash.returncode == py.returncode == ps.returncode == 0, (
+        bash.stderr, py.stderr, ps.stderr,
+    )
+    names = {
+        json_stdout(bash)["BRANCH_NAME"],
+        json_stdout(py)["BRANCH_NAME"],
+        json_stdout(ps)["BRANCH_NAME"],
+    }
+    assert names == {"001-"}, names