AttachHelper

A tiny throwaway launcher run as a separate JVM process. It attaches to the Minecraft JVM by pid and loads the Tessera agent into it.

Why a separate process: a JVM attaching to itself is refused unless it was started with -Djdk.attach.allowAttachSelf=true (the guard reads the startup property snapshot, so it can't be flipped at runtime). An external process attaching to the target has no such restriction — so this lets TS mixins work without any launch flag. Uses reflection so it carries no compile-time dependency on jdk.attach.

Args: <targetPid> <agentJarPath>.