There's a few big differences between the Anthropic C compiler and pgrust. The C compiler was built mostly autonomously and as a clean room implementation. OTOH I'm steering codex and using the Postgres source code as a reference. That's leading to the implementation being based more on how pg does things than anything else. If you want to try it out, I compiled it to wasm so you can try it out here[0]. You'll see it's much more faithful to Postgres than a C compiler that doesn't handle type checks.

[0] https://pgrust.com/