fix: address PR review feedback for allow-existing-branch

- Make checkout failure fatal instead of suppressing with || true (bash)
- Check $LASTEXITCODE after git checkout in PowerShell
- Use Test-Path -PathType Leaf for spec file existence check (PS)
- Add PowerShell static assertion test for -AllowExistingBranch flag

Assisted-By: 🤖 Claude Code

Author: rhuss

scripts/bash/create-new-feature.sh

@@ -294,7 +294,10 @@ if [ "$HAS_GIT" = true ]; then
         if git branch --list "$BRANCH_NAME" | grep -q .; then
             if [ "$ALLOW_EXISTING" = true ]; then
                 # Switch to the existing branch instead of failing
-                git checkout "$BRANCH_NAME" 2>/dev/null || true
+                if ! git checkout "$BRANCH_NAME" 2>/dev/null; then
+                    >&2 echo "Error: Failed to switch to existing branch '$BRANCH_NAME'. Please resolve any local changes or conflicts and try again."
+                    exit 1
+                fi
             elif [ "$USE_TIMESTAMP" = true ]; then
                 >&2 echo "Error: Branch '$BRANCH_NAME' already exists. Rerun to get a new timestamp or use a different --short-name."
                 exit 1

scripts/powershell/create-new-feature.ps1

@@ -256,6 +256,10 @@ if ($hasGit) {
             if ($AllowExistingBranch) {
                 # Switch to the existing branch instead of failing
                 git checkout -q $branchName 2>$null | Out-Null
+                if ($LASTEXITCODE -ne 0) {
+                    Write-Error "Error: Branch '$branchName' exists but could not be checked out. Resolve any uncommitted changes or conflicts and try again."
+                    exit 1
+                }
             } elseif ($Timestamp) {
                 Write-Error "Error: Branch '$branchName' already exists. Rerun to get a new timestamp or use a different -ShortName."
                 exit 1
@@ -276,7 +280,7 @@ $featureDir = Join-Path $specsDir $branchName
 New-Item -ItemType Directory -Path $featureDir -Force | Out-Null
 
 $specFile = Join-Path $featureDir 'spec.md'
-if (-not (Test-Path $specFile)) {
+if (-not (Test-Path -PathType Leaf $specFile)) {
     $template = Resolve-Template -TemplateName 'spec-template' -RepoRoot $repoRoot
     if ($template -and (Test-Path $template)) {
         Copy-Item $template $specFile -Force

tests/test_timestamp_branches.py

@@ -403,3 +403,12 @@ def test_allow_existing_no_git(self, no_git_dir: Path):
             "No git feature",
         )
         assert result.returncode == 0, result.stderr
+
+
+class TestAllowExistingBranchPowerShell:
+    def test_powershell_supports_allow_existing_branch_flag(self):
+        """Static guard: PS script exposes and uses -AllowExistingBranch."""
+        contents = CREATE_FEATURE_PS.read_text(encoding="utf-8")
+        assert "-AllowExistingBranch" in contents
+        # Ensure the flag is referenced in script logic, not just declared
+        assert "AllowExistingBranch" in contents.replace("-AllowExistingBranch", "")