Fix flaky Windows tests: dispose file watchers and use retried cleanup

The root cause was twofold:

1. MultiFileSystemWatcher.addWatcher() never disposed the FileSystemWatcher
   object itself — only its event subscriptions. This leaked OS file handles
   on Windows, preventing temp directory deletion.

2. The tests used tmp's synchronous rimrafSync for cleanup, which has no
   retry logic for Windows' asynchronous handle release.

Fix:
- Dispose the FileSystemWatcher itself in MultiFileSystemWatcher
- Replace removeCallback with async fs.rm with maxRetries, giving Windows
  time to release handles between retries

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: cklin

extensions/ql-vscode/src/common/vscode/multi-file-system-watcher.ts

@@ -20,6 +20,7 @@ class WatcherCollection extends DisposableObject {
    */
   public addWatcher(pattern: GlobPattern, listener: (e: Uri) => void): void {
     const watcher = workspace.createFileSystemWatcher(pattern);
+    this.push(watcher);
     this.push(watcher.onDidCreate(listener));
     this.push(watcher.onDidChange(listener));
     this.push(watcher.onDidDelete(listener));

extensions/ql-vscode/test/vscode-tests/minimal-workspace/common/vscode/file-path-discovery.test.ts

@@ -7,6 +7,7 @@ import { EventEmitter, Uri, workspace } from "vscode";
 import { FilePathDiscovery } from "../../../../../src/common/vscode/file-path-discovery";
 import { basename, dirname, join } from "path";
 import { mkdirSync, readFileSync, rmSync, writeFileSync } from "fs";
+import { rm } from "fs/promises";
 import { dirSync } from "tmp";
 import { normalizePath } from "../../../../../src/common/files";
 import { extLogger } from "../../../../../src/common/logging/vscode/loggers";
@@ -60,7 +61,6 @@ class TestFilePathDiscovery extends FilePathDiscovery<TestData> {
 
 describe("FilePathDiscovery", () => {
   let tmpDir: string;
-  let tmpDirRemoveCallback: (() => void) | undefined;
 
   let workspaceFolder: WorkspaceFolder;
   let workspacePath: string;
@@ -81,11 +81,7 @@ describe("FilePathDiscovery", () => {
   let discovery: TestFilePathDiscovery;
 
   beforeEach(() => {
-    const t = dirSync({
-      unsafeCleanup: true,
-    });
-    tmpDir = normalizePath(t.name);
-    tmpDirRemoveCallback = t.removeCallback;
+    tmpDir = normalizePath(dirSync().name);
 
     workspaceFolder = {
       uri: Uri.file(join(tmpDir, "workspace")),
@@ -117,9 +113,14 @@ describe("FilePathDiscovery", () => {
     discovery = new TestFilePathDiscovery();
   });
 
-  afterEach(() => {
-    tmpDirRemoveCallback?.();
+  afterEach(async () => {
     discovery.dispose();
+    await rm(tmpDir, {
+      recursive: true,
+      force: true,
+      maxRetries: 10,
+      retryDelay: 200,
+    });
   });
 
   describe("initialRefresh", () => {

extensions/ql-vscode/test/vscode-tests/minimal-workspace/queries-panel/query-discovery.test.ts

@@ -4,6 +4,7 @@ import { QueryDiscovery } from "../../../../src/queries-panel/query-discovery";
 import { createMockApp } from "../../../__mocks__/appMock";
 import { basename, dirname, join } from "path";
 import { dirSync } from "tmp";
+import { rm } from "fs/promises";
 import {
   FileTreeDirectory,
   FileTreeLeaf,
@@ -15,7 +16,6 @@ import { LanguageContextStore } from "../../../../src/language-context-store";
 
 describe("Query pack discovery", () => {
   let tmpDir: string;
-  let tmpDirRemoveCallback: (() => void) | undefined;
 
   let workspacePath: string;
 
@@ -29,11 +29,7 @@ describe("Query pack discovery", () => {
   let discovery: QueryDiscovery;
 
   beforeEach(() => {
-    const t = dirSync({
-      unsafeCleanup: true,
-    });
-    tmpDir = t.name;
-    tmpDirRemoveCallback = t.removeCallback;
+    tmpDir = dirSync().name;
 
     const workspaceFolder = {
       uri: Uri.file(join(tmpDir, "workspace")),
@@ -52,9 +48,14 @@ describe("Query pack discovery", () => {
     discovery = new QueryDiscovery(app, queryPackDiscoverer, languageContext);
   });
 
-  afterEach(() => {
-    tmpDirRemoveCallback?.();
+  afterEach(async () => {
     discovery.dispose();
+    await rm(tmpDir, {
+      recursive: true,
+      force: true,
+      maxRetries: 10,
+      retryDelay: 200,
+    });
   });
 
   describe("buildQueryTree", () => {

extensions/ql-vscode/test/vscode-tests/minimal-workspace/queries-panel/query-pack-discovery.test.ts

@@ -1,24 +1,20 @@
 import { Uri, workspace } from "vscode";
 import { QueryPackDiscovery } from "../../../../src/queries-panel/query-pack-discovery";
 import { dirSync } from "tmp";
+import { rm } from "fs/promises";
 import { dirname, join } from "path";
 import { ensureDir, writeJSON } from "fs-extra";
 import { QueryLanguage } from "../../../../src/common/query-language";
 
 describe("Query pack discovery", () => {
   let tmpDir: string;
-  let tmpDirRemoveCallback: (() => void) | undefined;
 
   let workspacePath: string;
 
   let discovery: QueryPackDiscovery;
 
   beforeEach(() => {
-    const t = dirSync({
-      unsafeCleanup: true,
-    });
-    tmpDir = t.name;
-    tmpDirRemoveCallback = t.removeCallback;
+    tmpDir = dirSync().name;
 
     const workspaceFolder = {
       uri: Uri.file(join(tmpDir, "workspace")),
@@ -33,9 +29,14 @@ describe("Query pack discovery", () => {
     discovery = new QueryPackDiscovery();
   });
 
-  afterEach(() => {
-    tmpDirRemoveCallback?.();
+  afterEach(async () => {
     discovery.dispose();
+    await rm(tmpDir, {
+      recursive: true,
+      force: true,
+      maxRetries: 10,
+      retryDelay: 200,
+    });
   });
 
   describe("findQueryPack", () => {