Function revoke 

pub fn revoke(idx: u32) -> Value

Run a @@prevoke:<idx> thunk: mark the proxy dead so every trap throws.

The target handle is KEPT rather than nulled as 10.5.15 step 5 words it, because typeof is fixed at creation by whether the target was callable and V8 still answers 'function' for a revoked proxy of a function. Nothing can read the target through the proxy anymore — revoked is checked before any trap or fallback runs.