public @interface Generated

Marks a class the backend processors wrote, so a later pass knows its own work.

Both processors refuse to generate a class whose name is already taken, because the generated one would silently overwrite the developer’s in the output directory. That guard read its OWN previous output as such a class: an incremental build – mvn process-classes a second time, without a clean – scans target/classes, finds the router or dispatcher written by the first pass, and reports a collision. Every project using @RestController failed its second build and only a clean would fix it.

CLASS retention: the class file has to carry it so the next pass’s scanner can see it, and nothing reads it at runtime.