What is the ABI of the Result<> type?

snapshot_docs
uses Result<> type

For example,
args_sizes_get() -> Result<(size, size), errno>

This type does not seems to be a C type, but looks like a type in the Rust programming language.

I do not find ABI definition in BasicCABI, for type similar to Result<>

Does Result<> has the same layout as

#[repr(C)]
enum Result<T, E> {
   Ok(T),
   Err(E),
}

What the layout of the following Result<>?
args_get(argv: Pointer<Pointer<u8>>, argv_buf: Pointer<u8>) -> Result<(), errno>
args_sizes_get() -> Result<(size, size), errno>
fd_write(fd: fd, iovs: ciovec_array) -> Result<size, errno>

Start with snapshot_docs/docs.md and the BasicCABI.md reference named in the issue, then trace how WASI result types are specified and represented at the ABI boundary. A complete resolution would document whether Result<> has a defined layout and clarify the layouts of the listed function results, with examples that remove the current ambiguity.