fix(core): Guard loadModule default parameter against ESM scope

Default parameters are evaluated before the function body, so the bare `module`
default threw `ReferenceError: module is not defined` from the ESM build before
reaching the try/catch that is meant to make `loadModule` degrade gracefully.
Guard it with a `typeof module` check so ESM callers get `undefined` instead.

Fixes #24117
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

Author: chargome

dev-packages/node-integration-tests/suites/esm/load-module/app.mjs

@@ -0,0 +1,6 @@
+import { loadModule } from '@sentry/core/server';
+
+// The default `existingModule` argument must not reference a CJS-only binding: default
+// parameters are evaluated before the function body, so a bare `module` would throw
+// outside the try/catch that is supposed to make this helper degrade gracefully.
+loadModule('node:path');

dev-packages/node-integration-tests/suites/esm/load-module/test.ts

@@ -0,0 +1,12 @@
+import { afterAll, describe, test } from 'vitest';
+import { cleanupChildProcesses, createRunner } from '../../../utils/runner';
+
+afterAll(() => {
+  cleanupChildProcesses();
+});
+
+describe('loadModule', () => {
+  test('does not throw when called without `existingModule` from ESM', async () => {
+    await createRunner(__dirname, 'app.mjs').ensureNoErrorOutput().start().completed();
+  });
+});

packages/core/src/utils/node.ts

@@ -44,8 +44,14 @@ function dynamicRequire(mod: any, request: string): any {
  * @param existingModule module to use for requiring
  * @returns possibly required module
  */
-// eslint-disable-next-line @typescript-eslint/no-explicit-any
-export function loadModule<T>(moduleName: string, existingModule: any = module): T | undefined {
+export function loadModule<T>(
+  moduleName: string,
+  // Default parameters are evaluated before the body runs, so a bare `module` would throw a
+  // ReferenceError in ESM before reaching the try/catch below that makes this helper degrade
+  // gracefully. Guard it so the ESM build resolves to `undefined` instead of crashing.
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  existingModule: any = typeof module !== 'undefined' ? module : undefined,
+): T | undefined {
   let mod: T | undefined;
 
   try {

packages/core/test/lib/utils/node.test.ts

@@ -0,0 +1,20 @@
+import { describe, expect, it } from 'vitest';
+import { loadModule } from '../../../src/utils/node';
+
+// vitest's `module` shim has no `require`, so tests hand in an explicit CJS-like module object.
+const cjsModule = { require };
+
+describe('loadModule', () => {
+  it('loads a module via the given `existingModule`', () => {
+    const path = loadModule<{ join: unknown }>('path', cjsModule);
+    expect(path?.join).toBeTypeOf('function');
+  });
+
+  it('returns undefined for a module that cannot be resolved', () => {
+    expect(loadModule('@sentry/this-module-does-not-exist', cjsModule)).toBeUndefined();
+  });
+
+  it('returns undefined instead of throwing when `existingModule` cannot require', () => {
+    expect(loadModule('path', undefined)).toBeUndefined();
+  });
+});