Constant RACTOR_BLOCK_LIMITATION 

pub const RACTOR_BLOCK_LIMITATION: &str = "ruby-ractor-block-unprobed";

A Ractor.new block cannot call the probes: a non-main Ractor cannot read the receiver global, so a probe there raises where the untouched program ran. Nothing is inserted inside one; what only a probe could prove there is unmeasured and declared at the block.