Design

The binding is a thin native layer, and every rule below follows from that.

• Processing stays native. Parameter binding, percent-decoding, conversion, reply serialization and the blocking client calls run in the extension, and ucall/__init__.py only re-exports it. A handler’s signature is resolved once at registration, so a request costs a table walk and one call, and a typed handler never sees a Request object at all.
• 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.
• Ownership follows the request. A reply consumes its Request, a released request answers 500, views over a body pin it until released, and a Response frees itself.
• Handlers never stop a loop. An exception inside a handler or an authorizer reaches sys.unraisablehook and answers 500 or rejects the peer, and Ctrl+C raised inside one is re-armed for the main thread.
• Blocking stays simple. Every method looks as it would without asynchrony, and only a reply with file or path parts answers a Deferred.
• Deferred replies are symmetric through language idioms. A Deferred owns its outcome: wait() blocks, await borrows the running loop’s executor, and releasing it waits, as releasing any owner does. The verbs that may defer exist only on a DetachedRequest, so by type no polling thread waits on its own loop.
• No extra cost until used. Bytes-only replies keep their outcome on the stack, up to sixteen reply parts lay out on the stack, and a Deferred is the one allocation a file reply adds.
• No life of its own. The binding starts no threads, keeps no global state beyond imported helpers, and needs no async runtime, so it drops into any threading model.
• Statuses and modes are enums. ucall.Status, Backend, CPUClass, Security, Verb, BodyDelivery and LogLevel are enum.IntEnum classes, so nothing is ever compared as a string.