Every host that serves the Yaak UI — the desktop app today, the browser bridge and anything after it — imports these types and implements the commands against them. That is what keeps a request's shape from drifting between hosts, and it is why the TypeScript bindings (bindings/gen_rpc.ts, exposed to the frontend as @yaakapp-internal/rpc-schema) are generated from one place.

Nothing here depends on Tauri or on any host. Request structs are plain data, and so are the few response types declared here rather than in an engine crate. Command bodies live with the host that runs them.

Adding a command

Add its request struct and an entry in with_commands! in src/lib.rs.
Write the adapter in each host — the desktop's live in crates-tauri/yaak-app-client/src/rpc_ext.rs. A host that does not support the command still has to say so; a missing adapter fails to compile.
Regenerate the bindings: cargo test -p yaak-rpc-schema writes bindings/gen_rpc.ts, which is committed.

How hosts consume the list

with_commands! takes the name of a macro_rules! macro and calls it with the full name(Req) -> Res list. Each host writes a small macro that receives that list and builds its router:

macro_rules! register_commands {
    ( $( $name:ident ( $req:ty ) -> $res:ty ),* $(,)? ) => {
        pub fn build_router() -> RpcRouter<MyCtx> {
            let mut router = RpcRouter::new();
            $( router.register(stringify!($name), rpc_handler_async!($name)); )*
            router
        }
    };
}
yaak_rpc_schema::with_commands!(register_commands);

The schema decides what commands exist; the host decides how each one runs.