1.11.0 crashes on spawn with ERR_MODULE_NOT_FOUND for @mcp-ui/server

[MRIIOT]

Summary

mongodb-mcp-server@1.11.0 fails to start when spawned via npx -y mongodb-mcp-server@1.11.0. The process exits before any MCP handshake with ERR_MODULE_NOT_FOUND for a transitive dependency. 1.10.0 works fine in the same environment.

Reproduction

# Inside a Linux container, as a non-root user (e.g. uid 1001)
npx -y mongodb-mcp-server@1.11.0

Result (with no other env set):

Error [ERR_MODULE_NOT_FOUND]: Cannot find module '/home/worker/.npm/_npx/<hash>/node_modules/@mcp-ui/server/dist/index.mjs' imported from /home/worker/.npm/_npx/<hash>/node_modules/mongodb-mcp-server/dist/esm/tools/tool.js
Did you mean to import "@mcp-ui/server/dist/index.cjs"?
    at finalizeResolution (node:internal/modules/esm/resolve:275:11)
    ...
{
  code: 'ERR_MODULE_NOT_FOUND',
  url: 'file:///home/worker/.npm/_npx/<hash>/node_modules/@mcp-ui/server/dist/index.mjs'
}

The same npx -y mongodb-mcp-server@1.10.0 in the same environment starts cleanly and accepts JSON-RPC initialize over stdio. The server proceeds normally through [INFO] 1000003 - server: Server close requested on stdin EOF.

Root cause

mongodb-mcp-server@1.11.0 pulls in @mcp-ui/server@6.1.0 as a transitive dependency. That package's package.json#exports declares:

{
  ".": {
    "types":   "./dist/src/index.d.ts",
    "import":  "./dist/index.mjs",
    "require": "./dist/index.cjs"
  }
}

…but the published 6.1.0 tarball does not contain dist/index.mjs. Only dist/index.cjs is present. When mongodb-mcp-server's ESM code does import from @mcp-ui/server, Node resolves the import condition → dist/index.mjs → file missing → crash. The error message's "Did you mean to import dist/index.cjs?" confirms which file exists.

This appears to be a packaging bug in @mcp-ui/server@6.1.0 that surfaces only because mongodb-mcp-server@1.11.0 started depending on it (or upgraded its version). 1.10.0 was unaffected (different dep set / different resolution).

Environment

• node v22.22.3
• npm 10.9.8
• Linux container (debian-slim base), running as non-root worker user uid 1001
• Spawned via npx -y mongodb-mcp-server@1.11.0 (no global install)

Workaround

Pin to mongodb-mcp-server@1.10.0 until upstream @mcp-ui/server ships a tarball that matches its exports field (or mongodb-mcp-server updates its dep range to skip 6.1.0).

Suggested fixes (any one resolves)

1. mongodb-mcp-server pins @mcp-ui/server to a version that ships both .mjs and .cjs per its own exports declaration.
2. File upstream against @mcp-ui/server to either ship the .mjs or update exports to omit the import condition.
3. Cut a 1.11.1 patch with the dep fix.

Happy to test a prerelease if the team wants to try a fixed dep range before a public bump.

[github-actions]

Thanks for opening this issue. The ticket MCP-504 was created for internal tracking.

[MRIIOT]

Update: workaround verified, bug is npx-specific

Tested in the same Linux container, same node v22.22.3, same uid 1001:

Globally installed — works

$ npm install -g mongodb-mcp-server@1.11.0
added 411 packages in 35s
$ mongodb-mcp-server --version
1.11.0
$ MDB_MCP_CONNECTION_STRING=... mongodb-mcp-server
[WARNING] 1010001 - Atlas Local Initialization: ...
[INFO] 1002002 - telemetry: Telemetry is disabled.
[INFO] 1004003 - server: Detected a MongoDB connection string ...
[INFO] 1000002 - server: Server with version 1.11.0 started ...

Server initializes cleanly, accepts JSON-RPC, executes tools.

Via npx — crashes

$ npx -y mongodb-mcp-server@1.11.0
Error [ERR_MODULE_NOT_FOUND]: Cannot find module '...@mcp-ui/server/dist/index.mjs'

Diagnosis

The bug surfaces ONLY in npx -y's flat-cache install layout. With npm install -g's standard nested node_modules, @mcp-ui/server's exports.import = "./dist/index.mjs" declaration ends up resolving (presumably the published tarball does ship dist/index.mjs after all — the file is in there but npx's hoisting clobbers it, OR npm CLI auto-substitutes .cjs somehow). Worth investigating on the @mcp-ui/server side too.

Same diagnosis applies to 1.10.0 via npx — different missing module:

$ npx -y mongodb-mcp-server@1.10.0
Error: Cannot find package '.../fast-string-truncated-width/index.js'
imported from .../fast-string-width/dist/index.js
code: ERR_MODULE_NOT_FOUND

But npm install -g mongodb-mcp-server@1.10.0 works fine.

Recommendation for the README

Until the npx flat-cache resolution is sorted upstream, the README's npx -y mongodb-mcp-server example may want a sibling "if running in a container as a non-root user, install globally instead" callout. The "Install globally" pattern dodges the entire class.

Production workaround we shipped

Baked npm install -g mongodb-mcp-server@1.11.0 into the worker image, dropped npx -y from the MCP server config (command: "mongodb-mcp-server", empty args). Spawn went from ~25s wall (cold npx pull racing Claude Code's 30s handshake timeout) to sub-second.