feat: add USB fixture helpers for backup-mode testing

DEVELOPER_GUIDE.md

@@ -22,7 +22,7 @@ Clone and verify:
 git clone https://github.com/git-fire/git-testkit.git
 
 # or SSH
-# git clone git@github.com:git-fire/git-testkit.git
+git clone git@github.com:git-fire/git-testkit.git
 
 cd git-testkit
 go test ./...
@@ -34,6 +34,7 @@ go test ./...
 - `scenarios.go`: fluent scenario builder and predefined multi-repo scenarios.
 - `snapshots.go`: snapshot/restore utilities for expensive test setup reuse.
 - `fixtures_test.go`: external package tests (`testutil_test`) that validate public API usage.
+- `usb_fixtures.go` / `usb_fixtures_test.go`: USB volume root and `.git-fire` config helpers for backup-mode style tests.
 - `scenarios_test.go`: package-internal tests for scenario/snapshot behavior.
 
 ## Design principles

fixtures.go

@@ -218,8 +218,13 @@ func GetRemotes(t *testing.T, repoPath string) map[string]string {
 			remainder = strings.TrimSpace(remainder)
 		}
 
-		remainder = strings.TrimSuffix(remainder, " (fetch)")
-		remainder = strings.TrimSuffix(remainder, " (push)")
+		// Strip only the trailing git remote role suffix once so paths that end
+		// with text like " (push)" are not damaged by sequential TrimSuffix calls.
+		if strings.HasSuffix(remainder, " (fetch)") {
+			remainder = strings.TrimSuffix(remainder, " (fetch)")
+		} else if strings.HasSuffix(remainder, " (push)") {
+			remainder = strings.TrimSuffix(remainder, " (push)")
+		}
 
 		if name != "" && remainder != "" {
 			remotes[name] = remainder

fixtures_test.go

@@ -99,6 +99,31 @@ func TestCreateTestRepo_WithRemotePathContainingSpaces(t *testing.T) {
 	}
 }
 
+func TestCreateTestRepo_WithRemotePathContainingPushSuffix(t *testing.T) {
+	tmpDir := t.TempDir()
+	remotePath := filepath.Join(tmpDir, "origin (push)")
+	if err := os.MkdirAll(remotePath, 0755); err != nil {
+		t.Fatalf("Failed to create bare repo directory: %v", err)
+	}
+	testutil.RunGitCmd(t, tmpDir, "init", "--bare", remotePath)
+
+	repoPath := testutil.CreateTestRepo(t, testutil.RepoOptions{
+		Name: "remote-push-suffix-repo",
+		Remotes: map[string]string{
+			"origin": remotePath,
+		},
+	})
+
+	remotes := testutil.GetRemotes(t, repoPath)
+	originURL, exists := remotes["origin"]
+	if !exists {
+		t.Fatal("Expected 'origin' remote to be configured")
+	}
+	if originURL != remotePath {
+		t.Fatalf("Expected origin URL %q, got %q", remotePath, originURL)
+	}
+}
+
 func TestCreateBareRemote(t *testing.T) {
 	remotePath := testutil.CreateBareRemote(t, "test-remote")
 

usb_fixtures.go

@@ -167,14 +167,24 @@ func ReadUSBVolumeConfig(t *testing.T, root string) USBVolumeConfig {
 func AssertGitDirAt(t *testing.T, path string, wantBare bool) {
 	t.Helper()
 	if wantBare {
-		if _, err := os.Stat(filepath.Join(path, "HEAD")); err != nil {
+		headPath := filepath.Join(path, "HEAD")
+		info, err := os.Stat(headPath)
+		if err != nil {
 			t.Fatalf("expected bare repo at %s: %v", path, err)
 		}
+		if info.IsDir() {
+			t.Fatalf("expected bare repo HEAD file at %s", path)
+		}
 		return
 	}
-	if _, err := os.Stat(filepath.Join(path, ".git")); err != nil {
+	gitPath := filepath.Join(path, ".git")
+	info, err := os.Stat(gitPath)
+	if err != nil {
 		t.Fatalf("expected non-bare repo at %s: %v", path, err)
 	}
+	if !info.IsDir() {
+		t.Fatalf("expected non-bare repo .git directory at %s", path)
+	}
 }
 
 func FileURLForPath(t *testing.T, path string) string {