Dropping NEXT_PUBLIC_ is not enough: static routes still bake env at build

Making a Next.js App Router value runtime-configurable has two independent build-time traps and fixing one silently leaves the other. First, any NEXT_PUBLIC_ name is inlined by the compiler even in server-only files that never reach a browser bundle, so the prefix freezes the value into the image. Second, and easy to miss: robots.ts and sitemap.ts are PRERENDERED by default -- they show as circle-marked Static in the build output -- so process.env is read during next build regardless of what the variable is called. Renaming alone produces a fix that compiles, passes review, and still ships a frozen value. Add export const dynamic = "force-dynamic" and confirm the route flips to the f marker in the build summary; that output table is the cheapest verification that a route is actually per-request. The general rule: for anything that must vary per deployment from one shared image, check the build output for which routes are static before believing an env change took effect.