from what i understand after a quick look at the source is it uses a C ABI to communicate between the WebView/CEF "host" application and the deno runtime which is loaded by the host as a shared library.

marshalling of values back and forth between the JS/C++/Rust layers still has to happen but these are just straight C api calls in process under the hood so much less overhead than having to do serdes across a socket/pipe.

- https://github.com/denoland/deno/blob/main/cli/rt_desktop/li...

- https://github.com/littledivy/laufey/blob/main/webview/src/m...

also notable that deno has a very low overhead bindings layer for doing JS->C/C++/Rust/Native interop using v8 fastapi calls where possible.