I definitely like the uds/named pipes approach
Discussion
if you have a controller/worker process relation you can even use stdin/out
We got a NIP!
https://github.com/nostr-protocol/nips/pull/1222
The NIP covers UDS communication more generally. I wrote a reference implementation in Rust that uses JSON-RPC 2.0 requests/responses wrapped in NIP-04 events exactly as described in NIP-46:
https://crates.io/crates/nip-55
The crate comes with a very basic NIP-46-over-NIP-55 module: