# Design

> UCall for Rust

The crate is a thin layer over UCall's native library, and every rule below follows from that.

- __Verbs share one name across languages.__
  `take_call`, `take_calls`, `take_batch`, `take_batches`, `submit` and `take_completed` name the same calls in Python and Rust.
- __Blocking stays simple, deferring stays symmetric.__
  A reply that is final on return looks as it did before files and streams existed, a deferred one is a `Deferred` that `wait`s, `.await`s or waits as it drops, and nothing costs more until a `DetachedRequest` is used.
- __Ownership is a type, not a flag.__
  A reply consumes its `Request`, a dropped request answers 500, only a `DetachedRequest` hands back a `Deferred`, a `Response` frees itself, and a `Client` is neither `Send` nor `Sync`, so misuse does not compile.
- __Single owners are claimed, never assumed.__
  Event loops and batch endpoints take `&self`, and an atomic claim answers `Status::Contended` to a second poller instead of racing it.
- __Handlers are plain closures.__
  A panic inside a handler or an authorizer is caught at the boundary, answering 500 or rejecting the peer, and never unwinds through C.
- __Polling allocates nothing.__
  A client sizes its tables by its call budget once, and a batch endpoint reuses the slots it lends requests in.
- __No life of its own.__
  The crate starts no threads, keeps no global state and needs no async runtime, so it drops into any threading model.