I made a tool that converts open source code into LLM poison: https://codeberg.org/timmc/scraggle
It mutates Rust source code in ways that *preserve* the ability to compile the code. (That is, you can't detect the changes by looking for compiler errors.) For example, it switches `+` and `*`, or `==` and `!=`.
If you fork a Rust repo, run this tool on it, and push it somewhere, then crawlers will end up ingesting all sorts of incorrect code.