test(sdk): cover local V4 extension setup

packages/sdk-ts/src/browser/localBrowser.ts

@@ -51,6 +51,8 @@ export function localBrowserChromeFlags(
   const viewport = options.viewport ?? { width: 1280, height: 800 };
   const windowSizeFlag = `--window-size=${viewport.width},${viewport.height}`;
 
+  // The browser factory installs the packaged runtime through CDP after launch.
+  // Branded Chrome ignores --load-extension, so do not claim it is preloaded here.
   return [
     ...(includeDefaults
       ? launcherDefaultFlags.filter(

packages/sdk-ts/tests/browser/localBrowser.test.ts

@@ -0,0 +1,45 @@
+import { describe, expect, it } from "vitest";
+import { localBrowserChromeFlags, WEBMCP_CHROME_FLAG } from "../../src/browser/localBrowser.js";
+
+describe("localBrowserChromeFlags", () => {
+  const launcherDefaults = ["--disable-extensions", "--disable-background-networking"];
+
+  it("keeps extensions enabled for CDP installation without launch-time loading", () => {
+    expect(localBrowserChromeFlags({}, launcherDefaults, false)).toEqual([
+      "--disable-background-networking",
+      "--enable-unsafe-extension-debugging",
+      "--remote-allow-origins=*",
+      "--window-size=1280,800",
+      WEBMCP_CHROME_FLAG,
+    ]);
+  });
+
+  it("does not inject extension flags when default browser flags are disabled", () => {
+    expect(
+      localBrowserChromeFlags(
+        { ignoreDefaultArgs: true, args: ["--user-supplied"] },
+        launcherDefaults,
+        false,
+      ),
+    ).toEqual(["--user-supplied"]);
+  });
+
+  it("preserves headless and launch options", () => {
+    const flags = localBrowserChromeFlags(
+      {
+        headless: true,
+        devtools: true,
+        args: ["--custom-flag"],
+      },
+      launcherDefaults,
+      true,
+    );
+
+    expect(flags.slice(-4)).toEqual([
+      "--headless",
+      "--auto-open-devtools-for-tabs",
+      "--no-sandbox",
+      "--custom-flag",
+    ]);
+  });
+});