fix(scripts): improve git branch creation error handling (#2089)

* fix(scripts): improve git branch creation error handling

- Capture git checkout -b stderr for meaningful error reporting
- Skip redundant checkout when already on target branch
- Surface actual git error messages instead of generic fallback

Applies to both bash and PowerShell create-new-feature scripts.

* fix(scripts): improve git branch creation error handling

- Capture git checkout -b stderr for meaningful error reporting
- Skip redundant checkout when already on target branch
- Surface actual git error messages instead of generic fallback

Applies to both bash and PowerShell create-new-feature scripts.

* fix(scripts): use quiet mode for git checkout -b when capturing errors

Ensures branch_create_error is empty on success, matching variable semantics.

Author: grafvonb

scripts/bash/create-new-feature.sh

@@ -327,12 +327,17 @@ SPEC_FILE="$FEATURE_DIR/spec.md"
 
 if [ "$DRY_RUN" != true ]; then
     if [ "$HAS_GIT" = true ]; then
-        if ! git checkout -b "$BRANCH_NAME" 2>/dev/null; then
+        branch_create_error=""
+        if ! branch_create_error=$(git checkout -q -b "$BRANCH_NAME" 2>&1); then
+            current_branch="$(git rev-parse --abbrev-ref HEAD 2>/dev/null || true)"
             # Check if branch already exists
             if git branch --list "$BRANCH_NAME" | grep -q .; then
                 if [ "$ALLOW_EXISTING" = true ]; then
-                    # Switch to the existing branch instead of failing
-                    if ! git checkout "$BRANCH_NAME" 2>/dev/null; then
+                    # If we're already on the branch, continue without another checkout.
+                    if [ "$current_branch" = "$BRANCH_NAME" ]; then
+                        :
+                    # Otherwise switch to the existing branch instead of failing.
+                    elif ! git checkout "$BRANCH_NAME" 2>/dev/null; then
                         >&2 echo "Error: Failed to switch to existing branch '$BRANCH_NAME'. Please resolve any local changes or conflicts and try again."
                         exit 1
                     fi
@@ -344,7 +349,12 @@ if [ "$DRY_RUN" != true ]; then
                     exit 1
                 fi
             else
-                >&2 echo "Error: Failed to create git branch '$BRANCH_NAME'. Please check your git configuration and try again."
+                >&2 echo "Error: Failed to create git branch '$BRANCH_NAME'."
+                if [ -n "$branch_create_error" ]; then
+                    >&2 printf '%s\n' "$branch_create_error"
+                else
+                    >&2 echo "Please check your git configuration and try again."
+                fi
                 exit 1
             fi
         fi

scripts/powershell/create-new-feature.ps1

@@ -293,25 +293,33 @@ $specFile = Join-Path $featureDir 'spec.md'
 if (-not $DryRun) {
     if ($hasGit) {
         $branchCreated = $false
+        $branchCreateError = ''
         try {
-            git checkout -q -b $branchName 2>$null | Out-Null
+            $branchCreateError = git checkout -q -b $branchName 2>&1 | Out-String
             if ($LASTEXITCODE -eq 0) {
                 $branchCreated = $true
             }
         } catch {
-            # Exception during git command
+            $branchCreateError = $_.Exception.Message
         }
 
         if (-not $branchCreated) {
+            $currentBranch = ''
+            try { $currentBranch = (git rev-parse --abbrev-ref HEAD 2>$null).Trim() } catch {}
             # Check if branch already exists
             $existingBranch = git branch --list $branchName 2>$null
             if ($existingBranch) {
                 if ($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
+                    # If we're already on the branch, continue without another checkout.
+                    if ($currentBranch -eq $branchName) {
+                        # Already on the target branch — nothing to do
+                    } else {
+                        # Otherwise 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."
@@ -321,7 +329,11 @@ if (-not $DryRun) {
                     exit 1
                 }
             } else {
-                Write-Error "Error: Failed to create git branch '$branchName'. Please check your git configuration and try again."
+                if ($branchCreateError) {
+                    Write-Error "Error: Failed to create git branch '$branchName'.`n$($branchCreateError.Trim())"
+                } else {
+                    Write-Error "Error: Failed to create git branch '$branchName'. Please check your git configuration and try again."
+                }
                 exit 1
             }
         }