VelocityDebugSwitch
Reads which debug categories the proxy should log.
The proxy has no configuration file of its own and is not getting one: a file means a parser, a parser means a dependency, and platform-velocity deliberately ships without so much as Ktor. A system property and an environment variable cost nothing and are both reachable from the command line and from a compose file.
The proxy is also shared by every backend, so this is deliberately not carried over the handshake: one Paper server's debug: true must not decide how much the proxy logs for everyone else.