mcp: surface task statusMessage notifications in chat progress (#298369)

- When a tool call returns a CreateTaskResult, the MCP server now forwards
  task statusMessage from notifications/tasks/status into the chat progress
  stream via the ToolProgress callback
- Adds onStatusMessage optional callback to McpTask constructor to report
  status messages as they come in from server notifications
- Updates callTool method signature to accept onStatusMessage callback,
  passed from _callWithProgress in mcpServer.ts
- This allows task-mode MCP tools to communicate progress through the
  established progress channel without requiring duplicate progress
  notifications

Fixes #298013

(Commit message generated by Copilot)

Author: connor4312

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

@@ -1087,7 +1087,7 @@ export class McpTool implements IMcpTool {
 					arguments: params,
 					task: shouldUseTask ? {} : undefined,
 					_meta: meta,
-				}, token);
+				}, token, progress ? (message) => progress.report({ message }) : undefined);
 
 				// Wait for tools to refresh for dynamic servers (#261611)
 				await this._server.awaitToolRefresh();

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

@@ -514,11 +514,11 @@ export class McpServerRequestHandler extends Disposable {
 	/**
 	 * Call a specific tool. Supports tasks automatically if `task` is set on the request.
 	 */
-	async callTool(params: MCP.CallToolRequest['params'] & MCP.Request['params'], token?: CancellationToken): Promise<MCP.CallToolResult> {
+	async callTool(params: MCP.CallToolRequest['params'] & MCP.Request['params'], token?: CancellationToken, onStatusMessage?: (message: string) => void): Promise<MCP.CallToolResult> {
 		const response = await this.sendRequest<MCP.CallToolRequest, MCP.CallToolResult | MCP.CreateTaskResult>({ method: 'tools/call', params }, token);
 
 		if (isTaskResult(response)) {
-			const task = new McpTask<MCP.CallToolResult>(response.task, token);
+			const task = new McpTask<MCP.CallToolResult>(response.task, token, onStatusMessage);
 			this._taskManager.adoptClientTask(task);
 			task.setHandler(this);
 			return task.result.finally(() => {
@@ -603,7 +603,8 @@ export class McpTask<T extends MCP.Result> extends Disposable implements IMcpTas
 
 	constructor(
 		private readonly _task: MCP.Task,
-		_token: CancellationToken = CancellationToken.None
+		_token: CancellationToken = CancellationToken.None,
+		private readonly _onStatusMessage?: (message: string) => void,
 	) {
 		super();
 
@@ -735,6 +736,9 @@ export class McpTask<T extends MCP.Result> extends Disposable implements IMcpTas
 
 	onDidUpdateState(task: MCP.Task) {
 		this._lastTaskState.set(task, undefined);
+		if (task.statusMessage && this._onStatusMessage) {
+			this._onStatusMessage(task.statusMessage);
+		}
 	}
 
 	setHandler(handler: McpServerRequestHandler | undefined): void {