fix(docs): Add Next.js Node.js runtime instrumentation guidance

Author: RulaKhaled

docs/platforms/javascript/common/configuration/integrations/openai.mdx

@@ -140,9 +140,37 @@ The integration will automatically detect streaming vs non-streaming requests an
 
 <PlatformSection supported={['javascript.nextjs']}>
 
-## Edge runtime
+## Node.js Runtime
 
-This integration is automatically instrumented in the Node.js runtime. For Next.js applications using the Edge runtime, you need to manually instrument the OpenAI client:
+Automatic instrumentation of the OpenAI SDK may not work as expected with certain Next.js configurations (especially with Turbopack and in Next.js 16). In these cases, manual instrumentation via `instrumentOpenAiClient` is recommended.
+
+For projects using Next.js 15 or earlier with Webpack, the following configuration can be applied in your `next.config.js` to ensure proper instrumentation:
+
+```javascript
+module.exports = {
+  webpack(config, { isServer }) {
+    if (isServer) {
+      // Force 'openai' to be required dynamically (not bundled)
+      // This allows Sentry to instrument the OpenAI SDK at runtime
+      config.externals = config.externals || [];
+      config.externals.push("openai");
+    }
+    return config;
+  },
+};
+```
+
+This ensures the package is externalized at runtime.
+
+<Note>
+
+This cannot be achieved using `serverExternalPackages: ['openai']`.
+
+</Note>
+
+## Edge Runtime
+
+For Next.js applications using the Edge runtime, you need to manually instrument the OpenAI client:
 
 ```javascript
 import * as Sentry from "@sentry/nextjs";