parentApiVersion

P as "major.minor" for the snippet compiler's -api-version/-language-version in SPLIT; null in SHARE_ALL, where the two kotlins are one and no pin is needed.

Floored at V2_0, which the compiler will not go below. Pinning ABOVE P costs nothing: a snippet compiles against the same kotlin jar it then runs on — the game's — so the compiler cannot offer an API the runtime lacks, whatever the pin allows.