test(e2e): address the Copilot review on the merged e2e PR

Three findings from the Copilot review of #984:
- server-env.test.ts assumed JLAB_DESKTOP_CONFIG_DIR was unset, so a developer
  or CI with it set would fail the userData-dir assertion. Save and clear it in
  beforeEach, restore in afterEach, so both cases are hermetic.
- start() polls the server URL via http/https.request and reschedules a 500ms
  setTimeout retry; with no real server that left background timers and
  connection attempts running after the assertions. Mock http/https so the poll
  reports the server up immediately and nothing stays scheduled, and swallow the
  now-resolving start() promise.
- the e2e install step only confirmed require('electron') resolved a path; add an
  explicit test -x on the launcher (and keep the macOS framework test -f) so a
  dropped or non-executable binary fails the step with a clear error.

Note: AI-assisted (Claude Code). Manually verified: the two server-env tests
pass in ~0.3s with no hang, full unit suite 432 pass (eslint/tsc deferred to CI:
this branch is off master's TS 4.2 / ESLint 8 and the local node_modules is on
the Electron-42 branch's toolchain).

Author: notluquis

.github/workflows/e2e.yml

@@ -57,9 +57,11 @@ jobs:
             ditto -x -k "$zip" "$dist"
             printf 'Electron.app/Contents/MacOS/Electron' > node_modules/electron/path.txt
             test -f "$dist/Electron.app/Contents/Frameworks/Electron Framework.framework/Versions/A/Electron Framework"
+            test -x "$dist/Electron.app/Contents/MacOS/Electron"
           else
             unzip -q -o "$zip" -d "$dist"
             printf 'electron' > node_modules/electron/path.txt
+            test -x "$dist/electron"
           fi
           node -e "console.log('resolved electron:', require('electron'))"
       - run: yarn build

test/unit/server-env.test.ts

@@ -95,6 +95,23 @@ vi.mock('../../src/main/pythonenvdialog/pythonenvdialog', () => ({
   ManagePythonEnvironmentDialog: { Tab: { Settings: 'settings' } }
 }));
 
+// start() polls the server URL via http/https.request until it is up. Without a
+// real server those requests fail and reschedule a setTimeout retry, leaving
+// background timers and connection attempts running after the assertions. Report
+// the URL as up immediately so the poll resolves and nothing is left scheduled.
+vi.mock('http', () => ({
+  request: (_url: unknown, cb: (res: { statusCode: number }) => void) => {
+    queueMicrotask(() => cb({ statusCode: 200 }));
+    return { on: vi.fn(), end: vi.fn() };
+  }
+}));
+vi.mock('https', () => ({
+  request: (_url: unknown, cb: (res: { statusCode: number }) => void) => {
+    queueMicrotask(() => cb({ statusCode: 200 }));
+    return { on: vi.fn(), end: vi.fn() };
+  }
+}));
+
 import { JupyterServer } from '../../src/main/server';
 import { IEnvironmentType } from '../../src/main/tokens';
 
@@ -116,13 +133,25 @@ async function flush() {
   }
 }
 
+// Saved/cleared so the userData-dir assertion is hermetic: a developer or CI
+// with JLAB_DESKTOP_CONFIG_DIR set in the ambient env would otherwise make
+// start() legitimately prefer it and fail the first test.
+let originalConfigDir: string | undefined;
+
 beforeEach(() => {
   vi.clearAllMocks();
   mockExecFile.mockReturnValue(makeChild());
+  originalConfigDir = process.env.JLAB_DESKTOP_CONFIG_DIR;
+  delete process.env.JLAB_DESKTOP_CONFIG_DIR;
 });
 
 afterEach(() => {
   vi.restoreAllMocks();
+  if (originalConfigDir === undefined) {
+    delete process.env.JLAB_DESKTOP_CONFIG_DIR;
+  } else {
+    process.env.JLAB_DESKTOP_CONFIG_DIR = originalConfigDir;
+  }
 });
 
 describe('JupyterServer.start env isolation', () => {
@@ -137,7 +166,7 @@ describe('JupyterServer.start env isolation', () => {
       }
     });
 
-    server.start();
+    void server.start().catch(() => undefined);
     await flush();
 
     expect(mockExecFile).toHaveBeenCalledTimes(1);
@@ -146,32 +175,23 @@ describe('JupyterServer.start env isolation', () => {
   });
 
   it('prefers the JLAB_DESKTOP_CONFIG_DIR override over the userData dir', async () => {
-    const original = process.env.JLAB_DESKTOP_CONFIG_DIR;
     process.env.JLAB_DESKTOP_CONFIG_DIR = '/override/config';
-    try {
-      const server = new JupyterServer({
-        environment: {
-          path: '/envs/e2e/bin/python',
-          name: 'e2e',
-          type: IEnvironmentType.VirtualEnv,
-          versions: {},
-          defaultKernel: 'python3'
-        }
-      });
-
-      server.start();
-      await flush();
-
-      const options = mockExecFile.mock.calls[0][1] as {
-        env: NodeJS.ProcessEnv;
-      };
-      expect(options.env.JUPYTER_CONFIG_DIR).toBe('/override/config');
-    } finally {
-      if (original === undefined) {
-        delete process.env.JLAB_DESKTOP_CONFIG_DIR;
-      } else {
-        process.env.JLAB_DESKTOP_CONFIG_DIR = original;
+    const server = new JupyterServer({
+      environment: {
+        path: '/envs/e2e/bin/python',
+        name: 'e2e',
+        type: IEnvironmentType.VirtualEnv,
+        versions: {},
+        defaultKernel: 'python3'
       }
-    }
+    });
+
+    void server.start().catch(() => undefined);
+    await flush();
+
+    const options = mockExecFile.mock.calls[0][1] as {
+      env: NodeJS.ProcessEnv;
+    };
+    expect(options.env.JUPYTER_CONFIG_DIR).toBe('/override/config');
   });
 });