fix: enable sync io tracing in gateway watch

docs/help/debugging.md

@@ -96,6 +96,10 @@ add Node's sync I/O trace flag through the source runner:
 OPENCLAW_TRACE_SYNC_IO=1 pnpm openclaw gateway --force
 ```
 
+`pnpm gateway:watch` enables this flag by default for the watched Gateway child.
+Set `OPENCLAW_TRACE_SYNC_IO=0` to suppress Node sync I/O trace output in watch
+mode.
+
 ## Gateway watch mode
 
 For fast iteration, run the gateway under the file watcher:

scripts/watch-node.mjs

@@ -277,6 +277,9 @@ export async function runWatchMain(params = {}) {
   // The watcher owns process restarts; keep SIGUSR1/config reloads in-process
   // so inherited launchd/systemd markers do not make the child exit and stall.
   childEnv.OPENCLAW_NO_RESPAWN = "1";
+  if (isGatewayWatchCommand(deps.args) && childEnv.OPENCLAW_TRACE_SYNC_IO === undefined) {
+    childEnv.OPENCLAW_TRACE_SYNC_IO = "1";
+  }
   if (deps.args.length > 0) {
     childEnv.OPENCLAW_WATCH_COMMAND = deps.args.join(" ");
   }

src/infra/watch-node.test.ts

@@ -143,6 +143,7 @@ describe("watch-node script", () => {
             OPENCLAW_WATCH_MODE: "1",
             OPENCLAW_WATCH_SESSION: "1700000000000-4242",
             OPENCLAW_NO_RESPAWN: "1",
+            OPENCLAW_TRACE_SYNC_IO: "1",
             OPENCLAW_WATCH_COMMAND: "gateway --force",
           }),
         }),
@@ -155,6 +156,35 @@ describe("watch-node script", () => {
     });
   });
 
+  it("preserves explicit sync I/O trace overrides for gateway watch", async () => {
+    const { child, spawn, createWatcher, fakeProcess } = createWatchHarness();
+    await withTempDir({ prefix: "openclaw-watch-node-" }, async (cwd) => {
+      const runPromise = runWatch({
+        args: ["gateway", "--force"],
+        cwd,
+        createWatcher,
+        env: { OPENCLAW_TRACE_SYNC_IO: "0" },
+        lockDisabled: true,
+        process: fakeProcess,
+        spawn,
+      });
+
+      expect(spawn).toHaveBeenCalledWith(
+        "/usr/local/bin/node",
+        ["scripts/run-node.mjs", "gateway", "--force"],
+        expect.objectContaining({
+          env: expect.objectContaining({
+            OPENCLAW_TRACE_SYNC_IO: "0",
+          }),
+        }),
+      );
+
+      fakeProcess.emit("SIGINT");
+      await runPromise;
+      expect(child.kill).toHaveBeenCalledWith("SIGTERM");
+    });
+  });
+
   it("starts the runner before loading chokidar", async () => {
     const child = Object.assign(new EventEmitter(), {
       kill: vi.fn(() => {}),