node 24 ric cannot load handler directory

[everett1992]

Prior to node 24 a lambda handler could be a path to a directory, which would resolve the index.js, or main field from package.json.
I don't know if this was a documented or unintended feature, but it works as recently as node 22.

Reproduction

runtime: node24
handler: dir.handler

// dir/index.js
module.exports.handler = async (event) => {
    const response = {
      statusCode: 200,
      body: JSON.stringify('Hello from dir!'),
    };
    return response;
  };

Error with node 24

{
  "errorType": "Error",
  "errorMessage": "Directory import '/var/task/dir' is not supported resolving ES modules imported from /var/runtime/index.mjs\nDid you mean to import \"/var/task/dir/index.js\"?",
  "trace": [
    "Error [ERR_UNSUPPORTED_DIR_IMPORT]: Directory import '/var/task/dir' is not supported resolving ES modules imported from /var/runtime/index.mjs",
    "Did you mean to import \"/var/task/dir/index.js\"?",
    "    at finalizeResolution (node:internal/modules/esm/resolve:268:11)",
    "    at moduleResolve (node:internal/modules/esm/resolve:870:10)",
    "    at moduleResolveWithNodePath (node:internal/modules/esm/resolve:996:14)",
    "    at defaultResolve (node:internal/modules/esm/resolve:1039:79)",
    "    at #cachedDefaultResolve (node:internal/modules/esm/loader:757:20)",
    "    at ModuleLoader.resolve (node:internal/modules/esm/loader:734:38)",
    "    at ModuleLoader.getModuleJobForImport (node:internal/modules/esm/loader:317:38)",
    "    at onImport.tracePromise.__proto__ (node:internal/modules/esm/loader:685:36)",
    "    at TracingChannel.tracePromise (node:diagnostics_channel:350:14)",
    "    at ModuleLoader.import (node:internal/modules/esm/loader:684:21)"
  ]
}

[vivitali]

up, same error after updating to 4.0.1

[godcrampy]

Prior to Node 24, the RIC used its own logic to resolve handlers, which we had been trying to keep in line with Node's behavior over the years. This was a duplicated effort, and starting with Node 24 (RIC v4.0.1), we've defaulted to letting Node import the handler as a module.

Our documentation describes including the filename in the handler.