fix: ql-mcp server must handle vscode workspace folder changes

extensions/vscode/esbuild.config.js

@@ -41,6 +41,7 @@ const testSuiteConfig = {
     'test/suite/mcp-resource-e2e.integration.test.ts',
     'test/suite/mcp-server.integration.test.ts',
     'test/suite/mcp-tool-e2e.integration.test.ts',
+    'test/suite/workspace-folder-change.integration.test.ts',
     'test/suite/workspace-scenario.integration.test.ts',
   ],
   outdir: 'dist/test/suite',

extensions/vscode/src/extension.ts

@@ -81,19 +81,20 @@ export async function activate(
   context.subscriptions.push(
     vscode.workspace.onDidChangeConfiguration((e) => {
       if (e.affectsConfiguration('codeql-mcp')) {
-        logger.info('Configuration changed — rebuilding environment');
-        envBuilder.invalidate();
-        mcpProvider.fireDidChange();
+        logger.info('Configuration changed — requesting MCP server restart');
+        mcpProvider.requestRestart();
       }
     }),
   );
 
-  // Re-scan when workspace folders change
+  // Invalidate cached environment when workspace folders change.
+  // VS Code itself manages MCP server lifecycle when roots change
+  // (stopping and restarting the server as needed).  We just clear
+  // the cached env so the next server start picks up updated folders.
   context.subscriptions.push(
     vscode.workspace.onDidChangeWorkspaceFolders(() => {
-      logger.info('Workspace folders changed — refreshing watchers');
+      logger.info('Workspace folders changed — invalidating environment cache');
       envBuilder.invalidate();
-      mcpProvider.fireDidChange();
     }),
   );
 

extensions/vscode/src/server/mcp-provider.ts

@@ -20,6 +20,13 @@ export class McpProvider
   private readonly _onDidChange = new vscode.EventEmitter<void>();
   readonly onDidChangeMcpServerDefinitions = this._onDidChange.event;
 
+  /**
+   * Monotonically increasing counter, bumped by `requestRestart()`.
+   * Appended to the version string so that VS Code sees a genuinely new
+   * server definition and triggers a stop → restart cycle.
+   */
+  private _revision = 0;
+
   constructor(
     private readonly serverManager: ServerManager,
     private readonly envBuilder: EnvironmentBuilder,
@@ -29,18 +36,46 @@ export class McpProvider
     this.push(this._onDidChange);
   }
 
-  /** Notify VS Code that the MCP server definitions have changed. */
+  /**
+   * Soft notification: tell VS Code that definitions may have changed.
+   *
+   * Does NOT bump the version, so VS Code will re-query
+   * `provideMcpServerDefinitions()` / `resolveMcpServerDefinition()` but
+   * will NOT restart the server. Use for lightweight updates (file watcher
+   * events, extension changes, background install completion) where the
+   * running server can continue with its current environment.
+   */
   fireDidChange(): void {
     this._onDidChange.fire();
   }
 
+  /**
+   * Request that VS Code restart the MCP server with a fresh environment.
+   *
+   * Invalidates the cached environment and bumps the internal revision counter
+   * so that the next call to `provideMcpServerDefinitions()` returns a
+   * definition with a different `version` string. VS Code compares the new
+   * version to the running server's version and, seeing a change, triggers a
+   * stop → start cycle.
+   *
+   * Use for changes that require a server restart (configuration changes).
+   */
+  requestRestart(): void {
+    this.envBuilder.invalidate();
+    this._revision++;
+    this.logger.info(
+      `Requesting ql-mcp restart (revision ${this._revision})...`,
+    );
+    this._onDidChange.fire();
+  }
+
   async provideMcpServerDefinitions(
     _token: vscode.CancellationToken,
   ): Promise<vscode.McpStdioServerDefinition[]> {
     const command = this.serverManager.getCommand();
     const args = this.serverManager.getArgs();
     const env = await this.envBuilder.build();
-    const version = this.serverManager.getVersion();
+    const version = this.getEffectiveVersion();
 
     this.logger.info(
       `Providing MCP server definition: ${command} ${args.join(' ')}`,
@@ -66,4 +101,28 @@ export class McpProvider
     server.env = env;
     return server;
   }
+
+  /**
+   * Computes the version string for the MCP server definition.
+   *
+   * Always returns a concrete string so that VS Code has a reliable
+   * baseline for version comparison.  When `serverManager.getVersion()`
+   * returns `undefined` (the "latest" / unpinned case), the extension
+   * version is used as the base instead.
+   *
+   * After one or more `requestRestart()` calls, a `+rN` revision suffix
+   * is appended so that the version is always different from the
+   * previous one.  VS Code uses the version to decide whether to
+   * restart a running server: a changed version triggers a stop → start
+   * cycle.
+   */
+  private getEffectiveVersion(): string {
+    const base =
+      this.serverManager.getVersion() ??
+      this.serverManager.getExtensionVersion();
+    if (this._revision === 0) {
+      return base;
+    }
+    return `${base}+r${this._revision}`;
+  }
 }

extensions/vscode/test/extension.test.ts

@@ -50,6 +50,7 @@ vi.mock('../src/server/mcp-provider', () => ({
       resolveMcpServerDefinition: vi.fn().mockResolvedValue(undefined),
       onDidChangeMcpServerDefinitions: vi.fn(),
       fireDidChange: vi.fn(),
+      requestRestart: vi.fn(),
       dispose: vi.fn(),
     };
   }),
@@ -102,6 +103,8 @@ vi.mock('../src/bridge/environment-builder', () => ({
 
 import { activate, deactivate } from '../src/extension';
 import * as vscode from 'vscode';
+import { McpProvider } from '../src/server/mcp-provider';
+import { EnvironmentBuilder } from '../src/bridge/environment-builder';
 
 function createMockContext(): vscode.ExtensionContext {
   return {
@@ -168,4 +171,37 @@ describe('Extension', () => {
   it('should deactivate even if activate was never called', () => {
     expect(() => deactivate()).not.toThrow();
   });
+
+  it('should invalidate env cache on workspace folder changes', async () => {
+    // Capture the workspace folder change callback
+    let workspaceFolderChangeCallback: Function | undefined;
+    const spy = vi.spyOn(vscode.workspace, 'onDidChangeWorkspaceFolders').mockImplementation(
+      (cb: Function) => { workspaceFolderChangeCallback = cb; return { dispose: vi.fn() }; },
+    );
+
+    await activate(ctx);
+
+    // The extension should have registered a workspace folder change handler
+    expect(workspaceFolderChangeCallback).toBeDefined();
+
+    // Get the mock instances created during activation
+    const mcpProviderInstance = vi.mocked(McpProvider).mock.results[0]?.value;
+    const envBuilderInstance = vi.mocked(EnvironmentBuilder).mock.results[0]?.value;
+
+    // Reset call counts from activation
+    mcpProviderInstance.fireDidChange.mockClear();
+    mcpProviderInstance.requestRestart.mockClear();
+    envBuilderInstance.invalidate.mockClear();
+
+    // Simulate workspace folder change
+    workspaceFolderChangeCallback!();
+
+    // Cache invalidated immediately; no VS Code notification.
+    // VS Code manages MCP server lifecycle (stop/restart) when roots change.
+    expect(envBuilderInstance.invalidate).toHaveBeenCalledTimes(1);
+    expect(mcpProviderInstance.fireDidChange).not.toHaveBeenCalled();
+    expect(mcpProviderInstance.requestRestart).not.toHaveBeenCalled();
+
+    spy.mockRestore();
+  });
 });

extensions/vscode/test/fixtures/multi-root-workspace/test.code-workspace

@@ -1,6 +1,16 @@
 {
 	"folders": [
-		{ "path": "folder-a" },
-		{ "path": "folder-b" }
+		{
+			"path": "folder-a"
+		},
+		{
+			"path": "folder-b"
+		},
+		{
+			"path": "folder-c"
+		},
+		{
+			"path": "folder-d"
+		}
 	]
 }

extensions/vscode/test/server/mcp-provider.test.ts

@@ -7,6 +7,7 @@ function createMockServerManager() {
   return {
     getCommand: vi.fn().mockReturnValue('npx'),
     getArgs: vi.fn().mockReturnValue(['-y', 'codeql-development-mcp-server']),
+    getExtensionVersion: vi.fn().mockReturnValue('2.25.1'),
     getVersion: vi.fn().mockReturnValue(undefined),
     getDescription: vi.fn().mockReturnValue('npx -y codeql-development-mcp-server'),
     getInstallDir: vi.fn().mockReturnValue('/mock/install'),
@@ -111,6 +112,22 @@ describe('McpProvider', () => {
     expect(definitions).toHaveLength(1);
   });
 
+  it('should always provide a defined version string even when serverVersion is latest', async () => {
+    // When serverManager.getVersion() returns undefined ("latest" mode),
+    // the definition must still carry a concrete version string so that
+    // VS Code has a baseline for version comparison. An undefined initial
+    // version prevents VS Code from detecting changes after requestRestart().
+    serverManager.getVersion.mockReturnValue(undefined);
+    serverManager.getExtensionVersion.mockReturnValue('2.25.1');
+
+    const token = { isCancellationRequested: false, onCancellationRequested: vi.fn() };
+    const definitions = await provider.provideMcpServerDefinitions(token as any);
+
+    expect(definitions![0].version).toBeDefined();
+    expect(typeof definitions![0].version).toBe('string');
+    expect(definitions![0].version!.length).toBeGreaterThan(0);
+  });
+
   it('should pass version from serverManager when pinned', async () => {
     serverManager.getVersion.mockReturnValue('2.20.0');
 
@@ -120,6 +137,78 @@ describe('McpProvider', () => {
     expect(definitions![0].version).toBe('2.20.0');
   });
 
+  it('should not change version on fireDidChange (soft signal)', async () => {
+    const token = { isCancellationRequested: false, onCancellationRequested: vi.fn() };
+    const before = await provider.provideMcpServerDefinitions(token as any);
+    const versionBefore = before![0].version;
+
+    provider.fireDidChange();
+    const after = await provider.provideMcpServerDefinitions(token as any);
+
+    expect(after![0].version).toBe(versionBefore);
+  });
+
+  it('should produce a different version after requestRestart', async () => {
+    const token = { isCancellationRequested: false, onCancellationRequested: vi.fn() };
+    const before = await provider.provideMcpServerDefinitions(token as any);
+    const versionBefore = before![0].version;
+
+    provider.requestRestart();
+    const after = await provider.provideMcpServerDefinitions(token as any);
+    const versionAfter = after![0].version;
+
+    expect(versionAfter).toBeDefined();
+    expect(versionAfter).not.toBe(versionBefore);
+  });
+
+  it('should produce distinct versions after successive requestRestart calls', async () => {
+    const token = { isCancellationRequested: false, onCancellationRequested: vi.fn() };
+
+    provider.requestRestart();
+    const defs1 = await provider.provideMcpServerDefinitions(token as any);
+
+    provider.requestRestart();
+    const defs2 = await provider.provideMcpServerDefinitions(token as any);
+
+    expect(defs1![0].version).not.toBe(defs2![0].version);
+  });
+
+  it('should append revision to pinned version after requestRestart', async () => {
+    serverManager.getVersion.mockReturnValue('2.20.0');
+    const token = { isCancellationRequested: false, onCancellationRequested: vi.fn() };
+
+    provider.requestRestart();
+    const definitions = await provider.provideMcpServerDefinitions(token as any);
+
+    expect(definitions![0].version).toMatch(/^2\.20\.0\+r\d+$/);
+  });
+
+  it('should append revision to extension version after requestRestart when version is latest', async () => {
+    serverManager.getVersion.mockReturnValue(undefined);
+    serverManager.getExtensionVersion.mockReturnValue('2.25.1');
+    const token = { isCancellationRequested: false, onCancellationRequested: vi.fn() };
+
+    provider.requestRestart();
+    const definitions = await provider.provideMcpServerDefinitions(token as any);
+
+    expect(definitions![0].version).toMatch(/^2\.25\.1\+r\d+$/);
+  });
+
+  it('should fire change event when requestRestart is called', () => {
+    const listener = vi.fn();
+    provider.onDidChangeMcpServerDefinitions(listener);
+
+    provider.requestRestart();
+
+    expect(listener).toHaveBeenCalledTimes(1);
+  });
+
+  it('should invalidate env cache when requestRestart is called', () => {
+    provider.requestRestart();
+
+    expect(envBuilder.invalidate).toHaveBeenCalledTimes(1);
+  });
+
   it('should resolve definition by refreshing environment', async () => {
     const updatedEnv = { CODEQL_PATH: '/new/path', TRANSPORT_MODE: 'stdio' };
     envBuilder.build.mockResolvedValue(updatedEnv);