what is repro-next-66918 fr?

This is a bug report and demonstration project for Next.js, a popular framework for building web applications. The issue shows that API endpoints behave differently depending on whether you're developing the app locally or running it in production mode. Here's the concrete problem: if you create an API endpoint that only handles two types of requests, GET (to fetch data) and PUT (to update data), it works fine when you're testing during development. But once you build and deploy the same code for production, the PUT requests stop working and return a "405 Method Not Allowed" error. The GET requests still work fine, but PUT requests are suddenly rejected. This shouldn't happen, the code is identical in both environments, so the behavior should be the same. The repository is essentially a minimal example that reproduces this bug so developers can see it happen themselves. Someone working on the Next.js framework would use this to understand and fix the underlying problem. A developer using Next.js might find it helpful to know about this issue if they're encountering the same problem in their own projects. The README walks through exactly how to trigger the bug: create a new Next.js app, add an API route with GET and PUT handlers, run it in development mode (where it works), then build it for production (where it breaks). This step-by-step approach makes it easy for others to verify they're experiencing the same issue or to test whether a fix actually resolves it.