This crate defines the "types" for the protocol used by LLMX CLI, which includes both "internal types" for communication between `llmx-core` and `llmx-tui`, as well as "external types" used with `llmx app-server`.
Ideally, we should avoid "material business logic" in this crate, as we can always introduce `Ext`-style traits to add functionality to types in other crates.
