[Bug]: [ERR_MODULE_NOT_FOUND]: Cannot find module when trying to import a @shared module inside the BFF methods

[vmary2014]

Version

System:
    OS: macOS 26.4.1
    CPU: (14) arm64 Apple M4 Pro
    Memory: 1.04 GB / 48.00 GB
    Shell: 5.9 - /bin/zsh
  Browsers:
    Chrome: 148.0.7778.98
    Firefox: 150.0.3
    Safari: 26.4
  npmPackages:
    @modern-js/app-tools: 3.1.5 => 3.1.5
    @modern-js/plugin-bff: 3.1.5 => 3.1.5
    @modern-js/runtime: 3.1.5 => 3.1.5
    @modern-js/server-runtime: 3.1.5 => 3.1.5
    @modern-js/tsconfig: 3.1.5 => 3.1.5

Details

Hello
Been trying modern.js and importing a @shared module inside a BFF.
I get this error below

Failed to load BFF module '/Users/project/api/lambda/health/live.ts': Error [ERR_MODULE_NOT_FOUND]: Cannot find module '/Users/project/shared/_logger' imported from /Users/project/api/lambda/health/live.ts
    at finalizeResolution (node:internal/modules/esm/resolve:275:11)
    at moduleResolve (node:internal/modules/esm/resolve:860:10)
    at defaultResolve (node:internal/modules/esm/resolve:984:11)
    at ModuleLoader.defaultResolve (node:internal/modules/esm/loader:685:12)
    at #cachedDefaultResolve (node:internal/modules/esm/loader:634:25)
    at ModuleLoader.getModuleJobForRequire (node:internal/modules/esm/loader:384:53)
    at new ModuleJobSync (node:internal/modules/esm/module_job:341:34)
    at ModuleLoader.importSyncForRequire (node:internal/modules/esm/loader:357:11)
    at loadESMFromCJS (node:internal/modules/cjs/loader:1385:24)
    at Module._compile (node:internal/modules/cjs/loader:1536:5) {
  code: 'ERR_MODULE_NOT_FOUND',
  url: 'file:///Users/project/shared/_logger

This is the vanilla modern.js so I didn't change anything in the tsconfig, plus changed the config js file to import the pluginBff

Any idea what I need to change?

Reproduce link

https://gist.github.com/vmary2014/781be5551dee299bb01f53eec827bbf0

Reproduce Steps

1 execute pnpm dev
2 getting the error at startup

[keepview]

This looks like a BFF dev runtime issue.

BFF dev loads api/lambda handlers directly at runtime. When a handler imports shared code like this:

import { logger } from "@shared/_logger";

@shared/* only exists in tsconfig.paths. Node does not understand this alias by itself, so the BFF runtime
must register a paths resolver before loading the handler.

In a vanilla project without ts-node, setupTsRuntime can skip runtime setup. Then @shared/_logger is passed
to Node unresolved, the BFF module fails to load, and the route is not registered.

There is also an ESM-specific issue. If the project has:

  {
    "type": "module"
  }

but inherits the default Modern.js base tsconfig, compilerOptions.module is still commonjs. After installing
ts-node, the handler can be compiled to CommonJS, but BFF loads it through ESM import. That causes:

ReferenceError: exports is not defined in ES module scope

Workaround:

pnpm add -D ts-node

For ESM projects, also set:

  {
    "compilerOptions": {
      "module": "ESNext",
      "moduleResolution": "Bundler"
    }
  }

Suggested framework fix:

1. BFF dev should always register tsconfig paths / Modern alias resolution before loading api/lambda modules.
2. It should not silently skip runtime setup when ts-node is absent.
3. For ESM projects, it should avoid compiling BFF handlers as CommonJS, or show a clear diagnostic when
   type: module conflicts with compilerOptions.module: commonjs.
4. Add an integration test where api/lambda/health/live.ts imports from @shared/_logger.

If there are still any questions, please provide a complete reproducible demo