refactor: use nginx -s reload instead of systemd

- doc: add comment

internal/hostnginx/controller_test.go

@@ -9,10 +9,12 @@ import (
 	"testing"
 )
 
-func TestControllerSwitchesAndReloadsExactService(t *testing.T) {
+// TestControllerSwitchesAndReloadsNginx 验证 Switch 能将活动端口切到 8080，
+// 且实际执行了 nginx -t 与 nginx -s reload 命令。
+func TestControllerSwitchesAndReloadsNginx(t *testing.T) {
 	configPath := writeNginxConfig(t, serverConfiguration)
 	runner := &recordingRunner{}
-	controller, err := newController(configPath, "/usr/sbin/nginx", "/bin/systemctl", "nginx.service", runner)
+	controller, err := newController(configPath, "/usr/sbin/nginx", runner)
 	if err != nil {
 		t.Fatalf("create host Nginx controller: %v", err)
 	}
@@ -30,17 +32,19 @@ func TestControllerSwitchesAndReloadsExactService(t *testing.T) {
 	}
 	wantCalls := [][]string{
 		{"/usr/sbin/nginx", "-t"},
-		{"/bin/systemctl", "reload", "--", "nginx.service"},
+		{"/usr/sbin/nginx", "-s", "reload"},
 	}
 	if !slices.EqualFunc(runner.calls, wantCalls, slices.Equal) {
 		t.Fatalf("unexpected host Nginx commands: %+v", runner.calls)
 	}
 }
 
+// TestControllerRestoresConfigurationWhenValidationFails 验证 nginx -t 校验失败时 Switch 返回错误，
+// 并把配置回滚为原始内容，同时执行了校验、回滚校验与回滚重载三次命令。
 func TestControllerRestoresConfigurationWhenValidationFails(t *testing.T) {
 	configPath := writeNginxConfig(t, serverConfiguration)
 	runner := &recordingRunner{errors: []error{errors.New("nginx test failed"), nil, nil}}
-	controller, err := newController(configPath, "/usr/sbin/nginx", "/bin/systemctl", "nginx.service", runner)
+	controller, err := newController(configPath, "/usr/sbin/nginx", runner)
 	if err != nil {
 		t.Fatalf("create host Nginx controller: %v", err)
 	}
@@ -57,10 +61,12 @@ func TestControllerRestoresConfigurationWhenValidationFails(t *testing.T) {
 	}
 }
 
+// TestControllerRestoreUsesCompleteSnapshot 验证 Restore 能使用 Switch 返回的完整快照
+// 把配置恢复到切换前的原始内容与活动端口。
 func TestControllerRestoreUsesCompleteSnapshot(t *testing.T) {
 	configPath := writeNginxConfig(t, serverConfiguration)
 	runner := &recordingRunner{}
-	controller, err := newController(configPath, "/usr/sbin/nginx", "/bin/systemctl", "nginx.service", runner)
+	controller, err := newController(configPath, "/usr/sbin/nginx", runner)
 	if err != nil {
 		t.Fatalf("create host Nginx controller: %v", err)
 	}
@@ -77,6 +83,8 @@ func TestControllerRestoreUsesCompleteSnapshot(t *testing.T) {
 	}
 }
 
+// writeNginxConfig 将 content 写入临时目录下的 nginx.conf 并返回其绝对路径，
+// 供 Controller 测试使用。写入失败会直接终止测试。
 func writeNginxConfig(t *testing.T, content string) string {
 	t.Helper()
 	path := filepath.Join(t.TempDir(), "nginx.conf")
@@ -86,11 +94,15 @@ func writeNginxConfig(t *testing.T, content string) string {
 	return path
 }
 
+// recordingRunner commandRunner 的测试实现，记录每次调用并依次返回预设的错误。
 type recordingRunner struct {
-	calls  [][]string
+	// calls 记录每次执行的命令（含参数）序列。
+	calls [][]string
+	// errors 依次返回的预设错误，取完后续调用返回 nil。
 	errors []error
 }
 
+// Run 记录本次调用命令，并按 errors 中的顺序返回下一个预设错误。
 func (r *recordingRunner) Run(_ context.Context, executable string, arguments ...string) error {
 	call := append([]string{executable}, arguments...)
 	r.calls = append(r.calls, call)