module: fix extensionless entry with explicit type=commonjs

lib/internal/modules/cjs/loader.js

@@ -1929,6 +1929,14 @@ Module._extensions['.js'] = function(module, filename) {
     } else {
       format = 'typescript';
     }
+  } else if (path.extname(filename) === '') {
+    // Extensionless files skip the .js suffix check above. When type: commonjs
+    // is explicit, force commonjs format so ESM syntax surfaces as SyntaxError
+    // instead of silently delegating to ESM.
+    pkg = packageJsonReader.getNearestParentPackageJSON(filename);
+    if (pkg?.data?.type === 'commonjs') {
+      format = 'commonjs';
+    }
   }
   const { source, format: loadedFormat } = loadSource(module, filename, format);
   // Function require shouldn't be used in ES modules when require(esm) is disabled.

test/es-module/test-extensionless-esm-type-commonjs.js

@@ -0,0 +1,50 @@
+'use strict';
+
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const path = require('node:path');
+const { spawnSync } = require('node:child_process');
+
+const tmpdir = require('../common/tmpdir');
+
+test('extensionless entry point with ESM syntax under type=commonjs should not silently exit 0', () => {
+  tmpdir.refresh();
+
+  const dir = tmpdir.resolve('extensionless-esm-commonjs');
+  fs.mkdirSync(dir, { recursive: true });
+
+  // package.json with type: commonjs
+  fs.writeFileSync(
+    path.join(dir, 'package.json'),
+    '{\n  "type": "commonjs"\n}\n',
+    'utf8'
+  );
+
+  // Extensionless executable with shebang + ESM syntax.
+  // NOTE: Execute via process.execPath to avoid PATH/env differences.
+  const scriptPath = path.join(dir, 'script'); // no extension
+  fs.writeFileSync(
+    scriptPath,
+    '#!/usr/bin/env node\n' +
+      "console.log('script STARTED')\n" +
+      "import { version } from 'node:process'\n" +
+      'console.log(version)\n',
+    'utf8'
+  );
+  fs.chmodSync(scriptPath, 0o755);
+
+  const r = spawnSync(process.execPath, ['./script'], {
+    cwd: dir,
+    encoding: 'utf8'
+  });
+
+  assert.ifError(r.error);
+
+  assert.notEqual(
+    r.status,
+    0,
+    `unexpected exit code 0; stdout=${JSON.stringify(r.stdout)} stderr=${JSON.stringify(r.stderr)}`
+  );
+  assert.ok(r.stderr && r.stderr.length > 0, 'expected stderr to contain an error message');
+});