bosh-nats-sync: remove dead code + fix runner test temp file leak

- Remove getCommandRunner() helper: now that NewUsersSync normalises a
  nil cmdRunner to DefaultCommandRunner at construction time, the nil
  check inside getCommandRunner() is unreachable. All call-sites updated
  to use u.commandRunner directly, which is always non-nil after New.

- Fix temp file leak in runner_test.go: dirSubjectFile and hmSubjectFile
  were created with os.CreateTemp but never removed in AfterEach. Promote
  them to suite-level variables and clean them up alongside natsConfigFile.

ai-assisted=yes
[TNZ-113908] Convert BOSH nats-sync job to Golang

Author: aramprice

src/bosh-nats-sync/pkg/runner/runner_test.go

@@ -25,6 +25,8 @@ var _ = Describe("Runner", func() {
 		logBuf             *bytes.Buffer
 		logger             *slog.Logger
 		natsConfigFile     *os.File
+		dirSubjectFile     *os.File
+		hmSubjectFile      *os.File
 		server             *httptest.Server
 		commandRunnerCalls []string
 		commandRunnerErr   error
@@ -40,11 +42,11 @@ var _ = Describe("Runner", func() {
 		Expect(err).NotTo(HaveOccurred())
 		Expect(os.WriteFile(natsConfigFile.Name(), []byte("{}"), 0644)).To(Succeed())
 
-		dirSubjectFile, err := os.CreateTemp("", "director-subject-*")
+		dirSubjectFile, err = os.CreateTemp("", "director-subject-*")
 		Expect(err).NotTo(HaveOccurred())
 		Expect(os.WriteFile(dirSubjectFile.Name(), []byte("C=USA, O=Cloud Foundry, CN=default.director.bosh-internal"), 0644)).To(Succeed())
 
-		hmSubjectFile, err := os.CreateTemp("", "hm-subject-*")
+		hmSubjectFile, err = os.CreateTemp("", "hm-subject-*")
 		Expect(err).NotTo(HaveOccurred())
 		Expect(os.WriteFile(hmSubjectFile.Name(), []byte("C=USA, O=Cloud Foundry, CN=default.hm.bosh-internal"), 0644)).To(Succeed())
 
@@ -103,6 +105,12 @@ var _ = Describe("Runner", func() {
 		if natsConfigFile != nil {
 			os.Remove(natsConfigFile.Name())
 		}
+		if dirSubjectFile != nil {
+			os.Remove(dirSubjectFile.Name())
+		}
+		if hmSubjectFile != nil {
+			os.Remove(hmSubjectFile.Name())
+		}
 		if server != nil {
 			server.Close()
 		}

src/bosh-nats-sync/pkg/userssync/users_sync.go

@@ -64,7 +64,11 @@ type UsersSync struct {
 
 // NewUsersSync builds a UsersSync from the parsed config. The runner uses this
 // for both the bootstrap and the periodic sync so the wiring lives in one place.
+// If cmdRunner is nil, DefaultCommandRunner is used.
 func NewUsersSync(cfg *config.Config, logger *slog.Logger, cmdRunner CommandRunner) *UsersSync {
+	if cmdRunner == nil {
+		cmdRunner = DefaultCommandRunner
+	}
 	return &UsersSync{
 		natsConfigFilePath:   cfg.NATS.ConfigFilePath,
 		boshConfig:           cfg.Director,
@@ -75,13 +79,6 @@ func NewUsersSync(cfg *config.Config, logger *slog.Logger, cmdRunner CommandRunn
 	}
 }
 
-func (u *UsersSync) getCommandRunner() CommandRunner {
-	if u.commandRunner != nil {
-		return u.commandRunner
-	}
-	return DefaultCommandRunner
-}
-
 func (u *UsersSync) Execute(ctx context.Context) error {
 	u.logger.Info("Executing NATS Users Synchronization")
 
@@ -143,7 +140,7 @@ func (u *UsersSync) Execute(ctx context.Context) error {
 
 		if currentFileHash != newFileHash {
 			u.logger.Info("NATS config changed, reloading NATS server")
-			if reloadErr := ReloadNATSServerConfig(u.natsServerExecutable, u.natsServerPIDFile, u.getCommandRunner()); reloadErr != nil {
+			if reloadErr := ReloadNATSServerConfig(u.natsServerExecutable, u.natsServerPIDFile, u.commandRunner); reloadErr != nil {
 				return reloadErr
 			}
 		}
@@ -189,7 +186,7 @@ func (u *UsersSync) Bootstrap() error {
 	if _, err := u.writeNATSConfigFile(nil, directorSubject, hmSubject); err != nil {
 		return fmt.Errorf("bootstrap: failed to write NATS config: %w", err)
 	}
-	if err := ReloadNATSServerConfig(u.natsServerExecutable, u.natsServerPIDFile, u.getCommandRunner()); err != nil {
+	if err := ReloadNATSServerConfig(u.natsServerExecutable, u.natsServerPIDFile, u.commandRunner); err != nil {
 		return fmt.Errorf("bootstrap: failed to reload NATS server config: %w", err)
 	}
 	u.logger.Info("Bootstrap: NATS config written and server reloaded")