Constant OPERATIONS 

const OPERATIONS: [Operation; 4];

Every hand-written unsafe operation the relaxation is there to permit.

One entry per operation, each carrying the argument that admits it. The inventory is compared by stable AST identity and local // SAFETY: text, not by line number, so formatting and movement within a file are free while replacing an operation is not.

The Send/Sync impls are on this list for the same reason as the blocks: each is a hand-written promise the compiler is taking on trust, and a promise about a raw pointer shared across threads is not a smaller one than a dereference of it.