fix(runtime): disable Playwright process signal handlers

packages/runtime/src/index.test.ts

@@ -138,6 +138,43 @@ describe("BrowserRuntime", () => {
     await rt.shutdown();
   });
 
+  it("disables Playwright process signal handlers so the host owns shutdown", async () => {
+    const { browser } = createMockBrowserTree();
+    mockChromiumLaunch.mockResolvedValueOnce(browser);
+
+    const rt = new BrowserRuntime({ headless: true });
+    await rt.createSession();
+    expect(mockChromiumLaunch).toHaveBeenCalledWith(
+      expect.objectContaining({
+        headless: true,
+        handleSIGINT: false,
+        handleSIGTERM: false,
+        handleSIGHUP: false,
+      }),
+    );
+    await rt.shutdown();
+  });
+
+  it("disables Playwright signal handlers on webkit fallback launch", async () => {
+    const { browser } = createMockBrowserTree();
+    mockChromiumLaunch.mockRejectedValueOnce(
+      new Error("browserType.launch: Executable doesn't exist"),
+    );
+    mockWebkitLaunch.mockResolvedValueOnce(browser);
+
+    const rt = new BrowserRuntime({ headless: false });
+    await rt.createSession();
+    expect(mockWebkitLaunch).toHaveBeenCalledWith(
+      expect.objectContaining({
+        headless: false,
+        handleSIGINT: false,
+        handleSIGTERM: false,
+        handleSIGHUP: false,
+      }),
+    );
+    await rt.shutdown();
+  });
+
   it("snapshots HTML with summarizeHtml and layered fields", async () => {
     const { browser } = createMockBrowserTree();
     mockChromiumLaunch.mockResolvedValueOnce(browser);

packages/runtime/src/index.ts

@@ -50,19 +50,27 @@ export class BrowserRuntime {
   }
 
   private async launchBrowser() {
+    /**
+     * Companion/MCP own process lifecycle (SIGINT/SIGTERM → graceful shutdown).
+     * Playwright defaults handleSIGINT/TERM to true and will close the browser
+     * then process.exit(130) on SIGINT, racing the host signal handlers.
+     */
+    const launchOptions = {
+      headless: this.options.headless ?? true,
+      handleSIGINT: false,
+      handleSIGTERM: false,
+      handleSIGHUP: false,
+    } as const;
+
     try {
-      return await chromium.launch({
-        headless: this.options.headless ?? true,
-      });
+      return await chromium.launch(launchOptions);
     } catch (chromiumError) {
       if (!shouldFallbackToWebkit(chromiumError)) {
         throw mapPlaywrightLaunchError(chromiumError);
       }
 
       try {
-        return await webkit.launch({
-          headless: this.options.headless ?? true,
-        });
+        return await webkit.launch(launchOptions);
       } catch (webkitError) {
         throw mapPlaywrightLaunchError(webkitError);
       }