> it seems crazy to me that Go's GC can Just Work with a VM you're writing in Go itself.

Far from it, it is more natural to do that than anything else.

Simplified example:

  type Array struct {
    items *any[]
  }

  type Object struct {
    fields map[string]*any
  }

These are the JVM values, and when the references to them disappear, the JVM values they reference can be GC'd as well.