C side of the Debugger object is intentionally tiny — it is a plain Io object with only a "type" slot stamped here; all stepping logic lives in Io-level code. The real wire-up happens in IoCoroutine.c: when a coroutine has debuggingOn, IoObject_performWithDebugger populates slots like message, messageSelf, messageLocals, messageCoroutine on this proto and resumes the coroutine stored in the Io-level `debuggerCoroutine` slot. That makes the debugger a regular Io coroutine paused in a receive loop, woken once per message send of the target coroutine.
Creates the Debugger proto: an empty IoObject with a `type` slot set to "Debugger". The method table is empty because all debugger methods are defined in Io (libs/iovm/io/Debugger.io). IoState stashes a pointer to this object in state->debugger so the coroutine trampoline in IoCoroutine.c can find it without a slot lookup.