fix(git): flip first flag immediately in ListWorktrees

The `first` flag (used to skip the main worktree entry) was not set
to `false` until the blank-line separator was encountered. This meant
that if the separator were ever missing, every linked worktree would
be silently skipped.

Move `first = false` into the `worktree` line handler where it
logically belongs, and simplify the empty-line handler accordingly.

Also replace a hand-rolled `contains` helper in tests with
`strings.Contains`.

Author: boneskull

internal/git/git.go

@@ -316,8 +316,8 @@ func (g *Git) ListWorktrees() (map[string]string, error) {
 
 		if wtPath, ok := strings.CutPrefix(line, "worktree "); ok {
 			if first {
-				// Mark that we've seen the main worktree header; we'll skip
-				// its branch line below.
+				// Skip the main worktree entry entirely.
+				first = false
 				currentPath = ""
 			} else {
 				currentPath = wtPath
@@ -336,9 +336,6 @@ func (g *Git) ListWorktrees() (map[string]string, error) {
 
 		// Empty line separates worktree entries
 		if line == "" {
-			if first {
-				first = false
-			}
 			currentPath = ""
 		}
 	}

internal/git/git_test.go

@@ -5,6 +5,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"strings"
 	"testing"
 
 	"github.com/boneskull/gh-stack/internal/git"
@@ -683,7 +684,7 @@ func TestGetResolvedGitDir(t *testing.T) {
 		t.Errorf("worktree git dir should differ from main repo git dir")
 	}
 	// Should contain "worktrees" in the path
-	if !contains(resolvedWtGitDir, "worktrees") {
+	if !strings.Contains(resolvedWtGitDir, "worktrees") {
 		t.Errorf("expected worktree git dir to contain 'worktrees', got %q", resolvedWtGitDir)
 	}
 }
@@ -708,20 +709,6 @@ func TestIsRebaseInProgressWorktree(t *testing.T) {
 	}
 }
 
-// contains checks if substr is in s (simple helper to avoid importing strings in test).
-func contains(s, substr string) bool {
-	return filepath.Base(s) == substr || len(s) >= len(substr) && searchString(s, substr)
-}
-
-func searchString(s, substr string) bool {
-	for i := 0; i <= len(s)-len(substr); i++ {
-		if s[i:i+len(substr)] == substr {
-			return true
-		}
-	}
-	return false
-}
-
 func TestRemoteBranchExists(t *testing.T) {
 	// Create main repo
 	dir := setupTestRepo(t)