dropIndexPoison

The enumerated classpath can include the vanilla obfuscated MC jar, with thousands of classes in the default (unnamed) package. Such a jar poisons the Kotlin scripting host's classpath index: with it on the compile cp the K2 frontend silently fails to resolve every other jar's packages (only net.minecraft survives, via mc-symbols). One default-package class is harmless; thousands break it. It's useless here anyway — we compile mojmap names against mc-symbols.jar. Identified by content (unnamed-package class count), never by filename, so it's launcher-independent; a mojmap-named MC jar is left untouched.