fix(scripts): keep PowerShell branch-name acronym match case-sensitive (parity with bash) (#3129)

* fix(scripts): keep PowerShell branch-name acronym match case-sensitive

Get-BranchName keeps a sub-3-character word only when it appears as an
UPPERCASE acronym in the description. The bash twin checks this
case-sensitively (grep "\b${word^^}\b" / grep -qw -- "${word^^}"), but the
PowerShell twin used -match, which is case-INSENSITIVE, so it kept EVERY
short word regardless of case -- contradicting its own comment and diverging
from bash. The same description then produced different spec-directory and
branch names on Windows/PowerShell vs macOS/Linux (e.g. "Add go support" ->
001-go-support instead of 001-support), desyncing specs/, feature.json, and
git branches across a mixed-OS team.

Use the case-sensitive -cmatch so a short word is kept only for a genuine
uppercase acronym, matching bash. Applied to both the core
scripts/powershell/create-new-feature.ps1 and the git extension's
create-new-feature-branch.ps1.

Add bash + PowerShell regression tests (core and git-extension) asserting a
lowercase short word is dropped while an uppercase acronym is kept.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* test: fix article grammar in branch-name docstrings

Address review: 'an UPPERCASE acronym' -> 'an acronym in UPPERCASE' across the four branch-name case-sensitivity test docstrings (the indefinite article reads cleanly before 'acronym'). Docstring-only; no behavior change.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/extensions/git/test_git_extension.py

@@ -298,6 +298,24 @@ class TestCreateFeatureBash:
         assert data["BRANCH_NAME"] == "001-user-auth"
         assert data["FEATURE_NUM"] == "001"
 
+    def test_branch_name_short_word_case_sensitivity(self, tmp_path: Path):
+        """A short word is dropped from the derived branch name unless it appears
+        as an acronym in UPPERCASE in the description (case-sensitive, must match the
+        PowerShell twin)."""
+        project = _setup_project(tmp_path)
+        # lowercase "go" (<3 chars, not an uppercase acronym) is dropped
+        r1 = _run_bash(
+            "create-new-feature-branch.sh", project, "--json", "--dry-run", "Add go support",
+        )
+        assert r1.returncode == 0, r1.stderr
+        assert json.loads(r1.stdout)["BRANCH_NAME"] == "001-support"
+        # uppercase "GO" is kept as an acronym
+        r2 = _run_bash(
+            "create-new-feature-branch.sh", project, "--json", "--dry-run", "Use GO now",
+        )
+        assert r2.returncode == 0, r2.stderr
+        assert json.loads(r2.stdout)["BRANCH_NAME"] == "001-use-go-now"
+
     def test_creates_branch_timestamp(self, tmp_path: Path):
         """Extension create-new-feature-branch.sh creates timestamp branch."""
         project = _setup_project(tmp_path)
@@ -426,6 +444,21 @@ class TestCreateFeaturePowerShell:
         data = json.loads(result.stdout)
         assert data["BRANCH_NAME"] == "001-user-auth"
 
+    def test_branch_name_short_word_case_sensitivity(self, tmp_path: Path):
+        """PowerShell must match the bash twin: a short word is dropped unless it
+        appears as an acronym in UPPERCASE (case-sensitive -cmatch, not -match)."""
+        project = _setup_project(tmp_path)
+        r1 = _run_pwsh(
+            "create-new-feature-branch.ps1", project, "-Json", "-DryRun", "Add go support",
+        )
+        assert r1.returncode == 0, r1.stderr
+        assert json.loads(r1.stdout)["BRANCH_NAME"] == "001-support"
+        r2 = _run_pwsh(
+            "create-new-feature-branch.ps1", project, "-Json", "-DryRun", "Use GO now",
+        )
+        assert r2.returncode == 0, r2.stderr
+        assert json.loads(r2.stdout)["BRANCH_NAME"] == "001-use-go-now"
+
     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")