Be glad you work on top of a relatively standardised platform! The C standard doesn't specify any details of the implementation backing rand(), so a bunch of platforms have wildly different implementations, and they change over time (FreeBSD swapped theirs out in 202, for example)

IIRC in the modern .NET runtime, System.Random should come from here, which is updated somewhat regularly: https://github.com/dotnet/runtime/commits/main/src/libraries.... Although, whether any of these is a behavioral breaking change isn't immediately clear; most are just API additions.

For what it’s worth, Claude did this without even being asked when I had it implement /dev/urandom in my deterministic dotnet runtime. (Fun fact: if the runtime only ever receives zero bytes from /dev/urandom then it will hang on attempting to initialise System.Random! That was the first way I asked for it to be implemented.)