> It is the programmer's responsibility when writing unsafe code to ensure that any safe code interacting with the unsafe code cannot trigger these behaviors. unsafe code that satisfies this property for any safe client is called sound; if unsafe code can be misused by safe code to exhibit undefined behavior, it is unsound.
Если возможно вызвать UB в safe-коде, то любой unsafe-код — unsound (что, очевидно, не то, что хотели сказать)