fix(dev): prevent duplicate backend launch and forward shutdown signals

scripts/dev-backend.mjs

@@ -1,8 +1,9 @@
 #!/usr/bin/env node
 // backend: 运行带 Air 热加载的 Go control-plane。
 import { spawn } from "node:child_process";
-import { readFileSync, existsSync } from "node:fs";
+import { readFileSync, existsSync, mkdirSync } from "node:fs";
 import { fileURLToPath } from "node:url";
+import { constants } from "node:os";
 import path from "node:path";
 
 const root = path.dirname(path.dirname(fileURLToPath(import.meta.url)));
@@ -40,9 +41,28 @@ if (!overrides.LOG_LEVEL) overrides.LOG_LEVEL = "debug";
 if (!overrides.NATIVE_GATEWAY_ENDPOINT) overrides.NATIVE_GATEWAY_ENDPOINT = "http://127.0.0.1:28187";
 
 const env = { ...process.env, ...overrides };
-const air = spawn("air", ["-c", ".air.toml", ...process.argv.slice(2)], {
+const lockDir = path.join(root, ".data");
+mkdirSync(lockDir, { recursive: true });
+// flock 持有锁直到 Air 及其子进程退出，拒绝重复启动，不争抢同一个程序文件。
+const air = spawn("flock", [
+  "--no-fork", "--nonblock", "--conflict-exit-code", "73",
+  path.join(lockDir, "dev-backend.lock"),
+  "air", "-c", ".air.toml", ...process.argv.slice(2),
+], {
   cwd: root,
   env,
   stdio: "inherit",
 });
-air.on("exit", (code) => process.exit(code ?? 0));
+for (const signal of ["SIGINT", "SIGTERM"]) {
+  process.on(signal, () => air.kill(signal));
+}
+air.on("error", (error) => {
+  console.error(`[dev-backend] 启动失败：${error.message}`);
+  process.exit(1);
+});
+air.on("exit", (code, signal) => {
+  if (code === 73) {
+    console.error("[dev-backend] 后台已在运行，拒绝重复启动。请停止原进程后再重启。");
+  }
+  process.exit(code ?? (128 + constants.signals[signal]));
+});