mcp: fix tools with empty descriptions cause a 400 error in copilot

src/vs/workbench/contrib/mcp/common/mcpServer.ts

@@ -255,7 +255,16 @@ export class McpServer extends Disposable implements IMcpServer {
 
 		const updateTools = (tx: ITransaction | undefined) => {
 			const toolPromise = handler.capabilities.tools ? handler.listTools({}, cts.token) : Promise.resolve([]);
-			this.toolsFromServerPromise.set(new ObservablePromise(toolPromise), tx);
+			const toolPromiseSafe = toolPromise.then(tools => tools.map(tool => {
+				if (!tool.description) {
+					// Ensure a description is provided for each tool, #243919
+					handler.logger.warn(`Tool ${tool.name} does not have a description. Tools must be accurately described to be called`);
+					tool.description = '<empty>';
+				}
+
+				return tool;
+			}));
+			this.toolsFromServerPromise.set(new ObservablePromise(toolPromiseSafe), tx);
 		};
 
 		store.add(handler.onDidChangeToolList(() => updateTools(undefined)));

src/vs/workbench/contrib/mcp/common/mcpServerRequestHandler.ts

@@ -114,7 +114,7 @@ export class McpServerRequestHandler extends Disposable {
 
 	protected constructor(
 		private readonly launch: IMcpMessageTransport,
-		private readonly logger: ILogger,
+		public readonly logger: ILogger,
 	) {
 		super();
 		this._register(launch.onDidReceiveMessage(message => this.handleMessage(message)));