WebSockets cost us $1M on our AWS bill

Chromium already has a zero-copy IPC mechanism that uses shared memory built-in. It's called Mojo. That's how the various browser processes talk to each other. They could just have passed mojo::BigBuffer messages to their custom.process and not had to worry about platform-specific code.

But writing a custom ring buffer implementation is also nice, I suppose...

The best way to find out something valuable is to be wrong on the Internet. Next time, bill them $10k for this secret!