Completion-based I/O

An asynchronous I/O model where the OS signals the program only after an operation has fully completed (as in io_uring or IOCP), rather than when a resource is merely ready, which clashes with Rust's readiness/poll-based futures and makes future cancellation prone to buffer-use-after-free.

grounded in: Trend theme 'Rust editions and concurrency pitfalls / hard debates about async concurrency models' grounded against the existing io-uring and poll-based-futures nodes.