fix: resilient VS Code download for integration tests

- Add retry logic (3 attempts) with backoff to download-vscode.js
- Handle unhandled promise rejections from @vscode/test-electron stream errors
- Clean partial downloads between retries to avoid checksum mismatches
- Default to 'stable' version to match .vscode-test.mjs configuration
- Chain download:vscode before vscode-test in test:integration script
- Cache VS Code downloads in build-and-test-extension.yml and copilot-setup-steps.yml
- Increase download timeout from 15s (default) to 120s

Fixes intermittent CI failures from ECONNRESET and empty-file checksum errors
when downloading VS Code for Extension Host integration tests.

Author: data-douser

extensions/vscode/.vscode-test.mjs

@@ -14,12 +14,21 @@
  */
 
 import { defineConfig } from '@vscode/test-cli';
+import { join } from 'path';
+import { fileURLToPath } from 'url';
+
+// Use a workspace-local .tmp path for user-data-dir to keep test artifacts
+// within the project. On macOS with deep workspace paths this may emit an
+// IPC socket length warning (>103 chars) — this is benign and non-blocking.
+const extensionRoot = fileURLToPath(new URL('.', import.meta.url));
+const userDataDir = join(extensionRoot, '.tmp', 'vsc-ud');
 
 export default defineConfig([
   {
     label: 'noWorkspace',
     files: 'dist/test/suite/*.test.cjs',
     version: 'stable',
+    launchArgs: ['--user-data-dir', userDataDir],
     mocha: {
       ui: 'tdd',
       color: true,
@@ -31,6 +40,7 @@ export default defineConfig([
     files: 'dist/test/suite/*.test.cjs',
     version: 'stable',
     workspaceFolder: './test/fixtures/single-folder-workspace',
+    launchArgs: ['--user-data-dir', userDataDir],
     mocha: {
       ui: 'tdd',
       color: true,
@@ -42,6 +52,7 @@ export default defineConfig([
     files: 'dist/test/suite/*.test.cjs',
     version: 'stable',
     workspaceFolder: './test/fixtures/multi-root-workspace/test.code-workspace',
+    launchArgs: ['--user-data-dir', userDataDir],
     mocha: {
       ui: 'tdd',
       color: true,

extensions/vscode/package.json

@@ -154,7 +154,7 @@
     "package": "vsce package --no-dependencies --out codeql-development-mcp-server-v$(node -e 'process.stdout.write(require(`./package.json`).version)').vsix",
     "test": "npm run test:coverage && npm run test:integration",
     "test:coverage": "vitest --run --coverage",
-    "test:integration": "vscode-test",
+    "test:integration": "npm run download:vscode && vscode-test",
     "test:integration:label": "vscode-test --label",
     "test:watch": "vitest --watch",
     "vscode:prepublish": "npm run clean && npm run lint && npm run bundle && npm run bundle:server",

extensions/vscode/scripts/download-vscode.js

@@ -12,14 +12,39 @@
  * Pass an explicit version (e.g. "1.110.0") to override.
  */
 
+import { existsSync, rmSync } from 'node:fs';
+import { join } from 'node:path';
 import { downloadAndUnzipVSCode } from '@vscode/test-electron';
 
 const MAX_RETRIES = 3;
 const version = process.argv[2] || 'stable';
 
+// @vscode/test-electron can emit unhandled rejections from internal stream
+// errors (e.g. ECONNRESET). Suppress them here so the retry loop can handle
+// the failure via the caught exception from the await.
+let suppressedError = null;
+process.on('unhandledRejection', (reason) => {
+  suppressedError = reason;
+  const msg = reason instanceof Error ? reason.message : String(reason);
+  console.error(`   (suppressed unhandled rejection: ${msg})`);
+});
+
+/**
+ * Remove partially-downloaded VS Code artifacts so the next attempt starts
+ * fresh instead of hitting a checksum mismatch on a truncated archive.
+ */
+function cleanPartialDownload() {
+  const cacheDir = join(new URL('..', import.meta.url).pathname, '.vscode-test');
+  if (existsSync(cacheDir)) {
+    console.log('   Cleaning .vscode-test/ to remove partial downloads...');
+    rmSync(cacheDir, { recursive: true, force: true });
+  }
+}
+
 console.log(`Downloading VS Code (${version}) for integration tests...`);
 
 for (let attempt = 1; attempt <= MAX_RETRIES; attempt++) {
+  suppressedError = null;
   try {
     const vscodeExecutablePath = await downloadAndUnzipVSCode({
       version,
@@ -31,6 +56,7 @@ for (let attempt = 1; attempt <= MAX_RETRIES; attempt++) {
     const message = error instanceof Error ? error.message : String(error);
     console.error(`❌ Attempt ${attempt}/${MAX_RETRIES} failed: ${message}`);
     if (attempt < MAX_RETRIES) {
+      cleanPartialDownload();
       const delayMs = attempt * 5_000;
       console.log(`   Retrying in ${delayMs / 1_000}s...`);
       await new Promise((resolve) => setTimeout(resolve, delayMs));