Struct ThreadRegistryEntry 

pub struct ThreadRegistryEntry {
    pub state: Rc<RefCell<LuaState>>,
    pub value: GcRef<LuaThread>,
}

One row of GlobalState::threads. Pairs the per-thread LuaState with the canonical GcRef<LuaThread> so every push_thread for the same id shares pointer-identity. Phase E-1 adds this; Phase E-2 extends it with interior-mutability bookkeeping when resume/yield need to mutate the child thread while the parent holds a borrow.

Fields

state: Rc<RefCell<LuaState>>

The owned coroutine LuaState. Wrapped in Rc<RefCell<...>> so that coroutine.resume can borrow the child mutably while the parent is still in scope. Single-threaded — borrows never overlap in practice because only one resume path is live at a time.

value: GcRef<LuaThread>

Canonical thread-value handle. Reused on every push so GcRef::ptr_eq is true across pushes.