feat: add t.openIsolatedSession() for multi-user e2e tests via CDP

Add the ability to open fully isolated browser sessions within a single
test. Each session gets its own Chrome browser context (separate cookies,
localStorage, sessionStorage, service workers) via CDP's
Target.createBrowserContext().

Includes 40 functional tests, selector chaining support, t2.run() for
transparent Selector/ClientFunction evaluation, and automatic cleanup.

Requires Native Automation mode (Chrome only).

Author: sam-yh

gulp/constants/functional-test-globs.js

@@ -1,4 +1,5 @@
 const MULTIPLE_WINDOWS_TESTS_GLOB      = 'test/functional/fixtures/multiple-windows/test.js';
+const ISOLATED_SESSIONS_TESTS_GLOB     = 'test/functional/fixtures/isolated-sessions/test.js';
 const HEADED_CHROME_FIREFOX_TESTS_GLOB = ['test/functional/fixtures/live/test.js', 'test/functional/fixtures/ui/test.js'];
 const COMPILER_SERVICE_TESTS_GLOB      = 'test/functional/fixtures/compiler-service/test.js';
 const LEGACY_TESTS_GLOB                = 'test/functional/legacy-fixtures/**/test.js';
@@ -12,13 +13,15 @@ const SCREENSHOT_TESTS_GLOB = [
 const TESTS_GLOB = [
     BASIC_TESTS_GLOB,
     `!${MULTIPLE_WINDOWS_TESTS_GLOB}`,
+    `!${ISOLATED_SESSIONS_TESTS_GLOB}`,
     `!${COMPILER_SERVICE_TESTS_GLOB}`,
 ];
 
 module.exports = {
     TESTS_GLOB,
     LEGACY_TESTS_GLOB,
     MULTIPLE_WINDOWS_TESTS_GLOB,
+    ISOLATED_SESSIONS_TESTS_GLOB,
     BASIC_TESTS_GLOB,
     COMPILER_SERVICE_TESTS_GLOB,
     SCREENSHOT_TESTS_GLOB,

src/api/test-controller/index.js

@@ -647,6 +647,23 @@ export default class TestController {
     [delegatedAPI(ReportCommand.methodName)] (...args) {
         return this.enqueueCommand(ReportCommand, { args });
     }
+
+    // Open an isolated browser session via CDP Target.createBrowserContext
+    _openIsolatedSession$ () {
+        const callsite = getCallsiteForMethod('openIsolatedSession');
+
+        return this._enqueueTask('openIsolatedSession', () => {
+            return async () => {
+                if (!this.testRun.isNativeAutomation)
+                    throw new Error('openIsolatedSession requires Native Automation mode');
+
+                const isolatedSession = await this.testRun.createIsolatedSession();
+
+                return isolatedSession.controller;
+            };
+        }, callsite);
+    }
+
     shouldStop (command) {
         // NOTE: should always stop on Debug command
         return command === 'debug';