I'm curious, how do these new runtimes handle async context tracking? Do they all rely on Async Hooks or implement their own solutions?

I'm not familiar with the term "context tracking", and management of the event loop is a bit lower level than I normally go, but I do know several runtimes use libuv (https://libuv.org) to handle asynchronous I/O, the same as Node.js (which it was created for).

I'm sure there will be JavaScript runtimes out there using some of Rust's asynchronous schedulers like tokio (https://docs.rs/tokio/latest/tokio/), too, but I wouldn't be surprised if a large number of them just do things bespoke.