Fix ask mode MCP tool availability after server discovery

extensions/copilot/src/extension/intents/node/askAgentIntent.ts

@@ -44,14 +44,40 @@ const getTools = (instaService: IInstantiationService, request: vscode.ChatReque
 		const lookForTags = new Set<string>(['vscode_codesearch']);
 		const endpointProvider = accessor.get<IEndpointProvider>(IEndpointProvider);
 		const model = await endpointProvider.getChatEndpoint(request);
-
-		// Special case...
-		// Since AskAgent currently has no tool picker, have to duplicate the toolReference logic here.
-		// When it's no longer experimental, it should be a custom mode, have a tool picker, etc.
-		// And must return boolean to avoid falling back on other logic that we don't want, like the `extension_installed_by_tool` check.
-		return toolsService.getEnabledTools(request, model, tool => tool.tags.some(tag => lookForTags.has(tag)) || request.toolReferences.some(ref => ref.name === tool.name));
+		return toolsService.getEnabledTools(request, model, tool => askAgentToolFilter(tool, request));
 	});
 
+/**
+ * Filters tools for the ask agent. Since AskAgent currently has no tool picker,
+ * we duplicate the toolReference logic here. When it's no longer experimental,
+ * it should be a custom mode, have a tool picker, etc.
+ *
+ * MCP tools are registered dynamically as the MCP server connects and discovers
+ * its tools. The `toolReferences` in the request are a snapshot taken when the
+ * request was parsed, which can happen before the MCP server finished
+ * discovering all of its tools. When the user referenced an MCP server (any of
+ * its tools appear in `toolReferences`), include all currently registered MCP
+ * tools so that availability reflects the live registration state rather than
+ * the possibly-stale snapshot. See #334569.
+ *
+ * Must return boolean to avoid falling back on other logic that we don't want,
+ * like the `extension_installed_by_tool` check.
+ */
+export function askAgentToolFilter(tool: vscode.LanguageModelToolInformation, request: vscode.ChatRequest): boolean {
+	const lookForTags = new Set<string>(['vscode_codesearch']);
+	if (tool.tags.some(tag => lookForTags.has(tag)) || request.toolReferences.some(ref => ref.name === tool.name)) {
+		return true;
+	}
+	if (tool.tags.includes('mcp')) {
+		// The user referenced an MCP server. MCP tools are registered with the
+		// `mcp_` prefix (see McpToolName.Prefix), so check the reference names
+		// rather than looking up the tool, which may not be registered yet when
+		// the request snapshot was taken.
+		return request.toolReferences.some(ref => ref.name.startsWith('mcp_'));
+	}
+	return false;
+}
+
 export class AskAgentIntent implements IIntent {
 
 	static readonly ID = Intent.AskAgent;

extensions/copilot/src/extension/intents/test/node/askAgentIntent.spec.ts

@@ -0,0 +1,73 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import { describe, expect, it } from 'vitest';
+import type { ChatRequest, LanguageModelToolInformation } from 'vscode';
+import { askAgentToolFilter } from '../../node/askAgentIntent';
+
+function makeTool(name: string, tags: string[] = []): LanguageModelToolInformation {
+	return {
+		name,
+		description: `description for ${name}`,
+		inputSchema: { type: 'object' },
+		tags,
+		source: undefined,
+	};
+}
+
+function makeRequest(toolReferences: { name: string }[]): ChatRequest {
+	return {
+		requestId: 'request-id',
+		message: 'test',
+		agentId: 'copilot-chat',
+		prompt: 'test',
+		references: [],
+		model: undefined,
+		toolReferences,
+		tools: [],
+		history: [],
+	};
+}
+
+describe('askAgentToolFilter', () => {
+	it('includes tools with the codesearch tag', () => {
+		const tool = makeTool('vscode_search', ['vscode_codesearch']);
+		const request = makeRequest([]);
+		expect(askAgentToolFilter(tool, request)).toBe(true);
+	});
+
+	it('includes tools referenced in the request', () => {
+		const tool = makeTool('vscode_read_file', []);
+		const request = makeRequest([{ name: 'vscode_read_file' }]);
+		expect(askAgentToolFilter(tool, request)).toBe(true);
+	});
+
+	it('excludes unreferenced non-MCP tools', () => {
+		const tool = makeTool('vscode_edit_file', []);
+		const request = makeRequest([]);
+		expect(askAgentToolFilter(tool, request)).toBe(false);
+	});
+
+	it('includes MCP tools when the user referenced an MCP server tool', () => {
+		// The request snapshot was taken while the MCP server was still
+		// discovering tools, so it only contains one of the server's tools.
+		const request = makeRequest([{ name: 'mcp_fire_take_snapshot' }]);
+		// Tools registered *after* the snapshot are now available too.
+		const tool = makeTool('mcp_fire_navigate_page', ['mcp']);
+		expect(askAgentToolFilter(tool, request)).toBe(true);
+	});
+
+	it('excludes MCP tools when the user did not reference an MCP server', () => {
+		const tool = makeTool('mcp_fire_navigate_page', ['mcp']);
+		const request = makeRequest([{ name: 'vscode_read_file' }]);
+		expect(askAgentToolFilter(tool, request)).toBe(false);
+	});
+
+	it('excludes MCP tools when the request has no tool references at all', () => {
+		const tool = makeTool('mcp_fire_navigate_page', ['mcp']);
+		const request = makeRequest([]);
+		expect(askAgentToolFilter(tool, request)).toBe(false);
+	});
+});