For your add(int32, int32) function: While an AI-generated implementation is not provably correct unless the test contains 2^64 inputs, I think it's pretty likely that a correct implementation would in fact be generated pretty quickly.
It may seem that a solution with assumptions like those are more complex than a simple addition operation, and thus the computer will find the addition solution first, but "simple" is a matter of perspective. Addition requires a logic cascade through the entire number, since the carries of the lower bits must be passed to the upper bits, which requires a critical path equal to the entire length of the inputs/outputs. In searching for an implementation which satisfies the few dozen/hundred test cases you feed it, making assumptions like those in the first paragraph can drastically shorten the critical path, and require far less logic since it's ignoring much of the input. Thus algorithmically, the addition operation may be seen as more complex.