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feat: hide MCP list tools #60

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0fd003e
fix: hide MCP list tools from client responses
csush May 21, 2026
d116ff1
chore(demo): remove MCP list tools rendering
csush May 21, 2026
b95c79f
fix: remove unused MCP list stream wrapper
csush May 21, 2026
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3 changes: 0 additions & 3 deletions demo/components/chat.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,6 @@ import React, { useCallback, useEffect, useRef, useState } from "react";
import ToolCall from "./tool-call";
import Message from "./message";
import Annotations from "./annotations";
import McpToolsList from "./mcp-tools-list";
import McpApproval from "./mcp-approval";
import { Item, McpApprovalRequestItem } from "@/lib/assistant";
import LoadingMessage from "./loading-message";
Expand Down Expand Up @@ -58,8 +57,6 @@ const Chat: React.FC<ChatProps> = ({ items, onSendMessage, onApprovalResponse })
<Annotations annotations={item.content[0].annotations} />
)}
</div>
) : item.type === "mcp_list_tools" ? (
<McpToolsList item={item} />
) : item.type === "mcp_approval_request" ? (
<McpApproval item={item as McpApprovalRequestItem} onRespond={onApprovalResponse} />
) : null}
Expand Down
22 changes: 1 addition & 21 deletions demo/lib/assistant.ts
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Expand Up @@ -46,13 +46,6 @@ export interface ToolCallItem {
}[];
}

export interface McpListToolsItem {
type: "mcp_list_tools";
id: string;
server_label: string;
tools: { name: string; description?: string }[];
}

export interface McpApprovalRequestItem {
type: "mcp_approval_request";
id: string;
Expand All @@ -61,7 +54,7 @@ export interface McpApprovalRequestItem {
arguments?: string;
}

@frac frac May 27, 2026 •
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@copilot Remove it from the demo, importing *.ts is a bad practice anyway.

export type Item = MessageItem | ToolCallItem | McpListToolsItem | McpApprovalRequestItem;
export type Item = MessageItem | ToolCallItem | McpApprovalRequestItem;

export const handleTurn = async (messages: any[], tools: any[], onMessage: (data: any) => void) => {
try {
Expand Down Expand Up @@ -477,19 +470,6 @@ export const processMessages = async () => {
console.log("response completed", data);
const { response } = data;

// Handle MCP tools list
const mcpListToolsMessage = response.output.find((m: Item) => m.type === "mcp_list_tools");

if (mcpListToolsMessage) {
chatMessages.push({
type: "mcp_list_tools",
id: mcpListToolsMessage.id,
server_label: mcpListToolsMessage.server_label,
tools: mcpListToolsMessage.tools || [],
});
setChatMessages([...chatMessages]);
}

// Handle MCP approval request
const mcpApprovalRequestMessage = response.output.find((m: Item) => m.type === "mcp_approval_request");

Expand Down
2 changes: 1 addition & 1 deletion src/routes/responses/closeOutputItem.ts
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Expand Up @@ -259,7 +259,7 @@ export async function* closeLastOutputItem(
sequence_number: SEQUENCE_NUMBER_PLACEHOLDER,
};
} else if (lastOutputItem?.type === "mcp_list_tools") {
// Already finalized by `listMcpToolsStream`; do not re-emit done.
// Internal MCP tool-list metadata is not client-visible; do not re-emit done.
} else {
throw new StreamingError(
`Not implemented: expected message, function_call, or mcp_call, got ${(lastOutputItem as ResponseOutputItem)?.type}`
Expand Down
2 changes: 1 addition & 1 deletion src/routes/responses/innerStream.test.ts
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Expand Up @@ -40,7 +40,7 @@ vi.mock("./handleOneTurn.js", () => ({

// Mock mcpStream
vi.mock("./mcpStream.js", () => ({
listMcpToolsStream: vi.fn(),
listMcpTools: vi.fn(),
callApprovedMCPToolStream: vi.fn(),
}));

Expand Down
15 changes: 3 additions & 12 deletions src/routes/responses/innerStream.ts
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Expand Up @@ -12,7 +12,7 @@ import { config } from "../../lib/config.js";
import { formatInputToMessages } from "./messageFormatting.js";
import { buildLLMPayload } from "./payloadBuilder.js";
import { handleOneTurnStream } from "./handleOneTurn.js";
import { listMcpToolsStream, callApprovedMCPToolStream } from "./mcpStream.js";
import { listMcpTools, callApprovedMCPToolStream } from "./mcpStream.js";

export async function* innerRunStream(
req: ValidatedRequest<CreateResponseParams>,
Expand Down Expand Up @@ -99,18 +99,9 @@ export async function* innerRunStream(
}
}
}
// Otherwise, list tools from MCP server
// Otherwise, list tools from MCP server for internal orchestration only.
if (!mcpListTools) {
for await (const event of listMcpToolsStream(tool, responseObject, traceContext, log)) {
yield event;
}
const lastOutput = responseObject.output.at(-1);
if (!lastOutput || lastOutput.type !== "mcp_list_tools") {
throw new Error(
`Expected mcp_list_tools output after listMcpToolsStream, got ${lastOutput?.type ?? "undefined"}`
);
}
mcpListTools = lastOutput;
mcpListTools = await listMcpTools(tool, traceContext, log);
}

// Only allowed tools are forwarded to the LLM
Expand Down
28 changes: 12 additions & 16 deletions src/routes/responses/mcpStream.test.ts
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Expand Up @@ -32,7 +32,7 @@ vi.mock("../../mcp.js", () => ({
connectMcpServer: vi.fn(),
}));

import { listMcpToolsStream, callApprovedMCPToolStream } from "./mcpStream.js";
import { listMcpTools, callApprovedMCPToolStream } from "./mcpStream.js";
import { connectMcpServer, callMcpTool } from "../../mcp.js";
import { createMockResponseObject, createMockLogger, collectEvents } from "./__test_helpers__/mocks.js";
import type { McpServerParams } from "../../schemas.js";
Expand All @@ -42,7 +42,7 @@ import type { Logger } from "pino";

const log = createMockLogger() as unknown as Logger;

describe("listMcpToolsStream", () => {
describe("listMcpTools", () => {
const traceContext = {} as Context;
const mcpTool: McpServerParams = {
server_label: "test-server",
Expand All @@ -57,7 +57,7 @@ describe("listMcpToolsStream", () => {
vi.clearAllMocks();
});

it("yields correct event sequence on success", async () => {
it("fetches tools internally without adding public response output or events", async () => {
const mockClient = {
listTools: vi.fn().mockResolvedValue({
tools: [
Expand All @@ -74,24 +74,20 @@ describe("listMcpToolsStream", () => {
(connectMcpServer as ReturnType<typeof vi.fn>).mockResolvedValue(mockClient);

const responseObject = createMockResponseObject();
const events = await collectEvents(listMcpToolsStream(mcpTool, responseObject, traceContext, log));
const types = events.map((e) => e.type);
const result = await listMcpTools(mcpTool, traceContext, log);

expect(types).toEqual([
"response.output_item.added",
"response.mcp_list_tools.in_progress",
"response.mcp_list_tools.completed",
"response.output_item.done",
]);
expect(types.filter((t) => t === "response.output_item.done")).toHaveLength(1);
expect(result).toMatchObject({
type: "mcp_list_tools",
server_label: "test-server",
tools: [{ name: "search", input_schema: { type: "object" }, description: "Search tool" }],
});
expect(responseObject.output).toEqual([]);
});
Comment on lines 74 to 85

it("yields failed event and throws on connection error", async () => {
it("throws on connection error without yielding public failure events", async () => {
(connectMcpServer as ReturnType<typeof vi.fn>).mockRejectedValue(new Error("Connection refused"));

const responseObject = createMockResponseObject();

await expect(collectEvents(listMcpToolsStream(mcpTool, responseObject, traceContext, log))).rejects.toThrow(
await expect(listMcpTools(mcpTool, traceContext, log)).rejects.toThrow(
"Failed to list tools from MCP server 'test-server'"
);
});
Expand Down
39 changes: 3 additions & 36 deletions src/routes/responses/mcpStream.ts
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Expand Up @@ -14,12 +14,11 @@ import {
} from "./types.js";
import { buildJsonAttribute, recordError } from "./utils.js";

export async function* listMcpToolsStream(
export async function listMcpTools(
tool: McpServerParams,
responseObject: IncompleteResponse,
traceContext: Context,
log: Logger
): AsyncGenerator<PatchedResponseStreamEvent> {
): Promise<ResponseOutputItem.McpListTools> {
const span = tracer.startSpan(
"gen_ai.execute_tool",
{
Expand All @@ -38,55 +37,23 @@ export async function* listMcpToolsStream(
server_label: tool.server_label,
tools: [],
};
responseObject.output.push(outputObject);

yield {
type: "response.output_item.added",
output_index: responseObject.output.length - 1,
item: outputObject,
sequence_number: SEQUENCE_NUMBER_PLACEHOLDER,
};

yield {
type: "response.mcp_list_tools.in_progress",
item_id: outputObject.id,
output_index: responseObject.output.length - 1,
sequence_number: SEQUENCE_NUMBER_PLACEHOLDER,
};

let mcp: Awaited<ReturnType<typeof connectMcpServer>> | undefined;
try {
mcp = await connectMcpServer(tool, log);
const mcpTools = await mcp.listTools();
yield {
type: "response.mcp_list_tools.completed",
item_id: outputObject.id,
output_index: responseObject.output.length - 1,
sequence_number: SEQUENCE_NUMBER_PLACEHOLDER,
};
outputObject.tools = mcpTools.tools.map((mcpTool) => ({
input_schema: mcpTool.inputSchema,
name: mcpTool.name,
annotations: mcpTool.annotations,
description: mcpTool.description,
}));
span.setAttribute("mcp.tools.count", outputObject.tools.length);
yield {
type: "response.output_item.done",
output_index: responseObject.output.length - 1,
item: outputObject,
sequence_number: SEQUENCE_NUMBER_PLACEHOLDER,
};
return outputObject;
} catch (error) {
const errorMessage = `Failed to list tools from MCP server '${tool.server_label}': ${error instanceof Error ? error.message : "Unknown error"}`;
log.error({ err: error, server_label: tool.server_label }, "Failed to list MCP tools");
recordError(span, error);
yield {
type: "response.mcp_list_tools.failed",
item_id: outputObject.id,
output_index: responseObject.output.length - 1,
sequence_number: SEQUENCE_NUMBER_PLACEHOLDER,
};
throw new Error(errorMessage);
} finally {
if (mcp) {
Expand Down
67 changes: 16 additions & 51 deletions tests/responses.test.js
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Expand Up @@ -497,23 +497,11 @@ describe("responses.js", function () {
});

assert.ok(Array.isArray(response.output));
assert.ok(response.output.length >= 2);

// Check first output item (mcp_list_tools)
const listToolsOutput = response.output[0];
assert.equal(listToolsOutput.type, "mcp_list_tools");
assert.equal(listToolsOutput.server_label, "gitmcp");
assert.ok(listToolsOutput.id);
assert.ok(Array.isArray(listToolsOutput.tools));
assert.ok(listToolsOutput.tools.length > 0);

// Check that tools array contains expected tools
const toolNames = listToolsOutput.tools.map((tool) => tool.name);
assert.ok(toolNames.includes("fetch_tiktoken_documentation"));
assert.ok(toolNames.includes("search_tiktoken_documentation"));

// Check second output item (mcp_call)
const mcpCallOutput = response.output[1];
assert.ok(response.output.length >= 1);
assert.ok(!response.output.some((item) => item.type === "mcp_list_tools"));

// Check first output item (mcp_call)
const mcpCallOutput = response.output[0];
assert.equal(mcpCallOutput.type, "mcp_call");
assert.equal(mcpCallOutput.name, "fetch_tiktoken_documentation");
assert.equal(mcpCallOutput.server_label, "gitmcp");
Expand Down Expand Up @@ -571,23 +559,11 @@ describe("responses.js", function () {
});

assert.ok(Array.isArray(response.output));
assert.ok(response.output.length === 2);

// Check first output item (mcp_list_tools)
const listToolsOutput = response.output[0];
assert.equal(listToolsOutput.type, "mcp_list_tools");
assert.equal(listToolsOutput.server_label, "gitmcp");
assert.ok(listToolsOutput.id);
assert.ok(Array.isArray(listToolsOutput.tools));
assert.ok(listToolsOutput.tools.length > 0);

// Check that tools array contains expected tools
const toolNames = listToolsOutput.tools.map((tool) => tool.name);
assert.ok(toolNames.includes("fetch_tiktoken_documentation"));
assert.ok(toolNames.includes("search_tiktoken_documentation"));

// Check second output item (mcp_approval_request)
const approvalRequestOutput = response.output[1];
assert.ok(response.output.length === 1);
assert.ok(!response.output.some((item) => item.type === "mcp_list_tools"));

// Check first output item (mcp_approval_request)
const approvalRequestOutput = response.output[0];
assert.equal(approvalRequestOutput.type, "mcp_approval_request");
assert.equal(approvalRequestOutput.name, "fetch_tiktoken_documentation");
assert.equal(approvalRequestOutput.server_label, "gitmcp");
Expand Down Expand Up @@ -616,23 +592,11 @@ describe("responses.js", function () {
});

assert.ok(Array.isArray(response.output));
assert.ok(response.output.length >= 2);

// Check first output item (mcp_list_tools)
const listToolsOutput = response.output[0];
assert.equal(listToolsOutput.type, "mcp_list_tools");
assert.equal(listToolsOutput.server_label, "gitmcp");
assert.ok(listToolsOutput.id);
assert.ok(Array.isArray(listToolsOutput.tools));
assert.ok(listToolsOutput.tools.length > 0);

// Check that tools array contains expected tools
const toolNames = listToolsOutput.tools.map((tool) => tool.name);
assert.ok(toolNames.includes("fetch_tiktoken_documentation"));
assert.ok(toolNames.includes("search_tiktoken_documentation"));

// Check second output item (mcp_call)
const mcpCallOutput = response.output[1];
assert.ok(response.output.length >= 1);
assert.ok(!response.output.some((item) => item.type === "mcp_list_tools"));

// Check first output item (mcp_call)
const mcpCallOutput = response.output[0];
assert.equal(mcpCallOutput.type, "mcp_call");
assert.equal(mcpCallOutput.name, "fetch_tiktoken_documentation");
assert.equal(mcpCallOutput.server_label, "gitmcp");
Expand Down Expand Up @@ -703,6 +667,7 @@ describe("responses.js", function () {

assert.ok(Array.isArray(response.output));
assert.ok(response.output.length === 1);
assert.ok(!response.output.some((item) => item.type === "mcp_list_tools"));

// Check that the first output item is an approval request (not a list_tools call)
const approvalRequestOutput = response.output[0];
Expand Down
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