Another choice is SaferCPlusPlus[1] (optionally with a framework like Wt[2]).
Using a higher level language (than C) arguably has the drawback of "hiding complexity" in exchange for better productivity and scalability. But languages like Rust and C++ (with SaferCPlusPlus) retain much of the intrinsic performance and memory efficiency of C, without introducing an additional runtime layer. That may allow you to employ extra (diverse) layers of sandboxing/jailing and other security/correctness solutions.
Using a higher level language (than C) arguably has the drawback of "hiding complexity" in exchange for better productivity and scalability. But languages like Rust and C++ (with SaferCPlusPlus) retain much of the intrinsic performance and memory efficiency of C, without introducing an additional runtime layer. That may allow you to employ extra (diverse) layers of sandboxing/jailing and other security/correctness solutions.
[1] shameless plug: https://github.com/duneroadrunner/SaferCPlusPlus
[2] https://www.webtoolkit.eu/wt