Loop.init/close, add_read/del_read/add_write/del_write with a
per-registration udata word, and wait() normalizing backend events
into Event{fd, udata, readable, writable, eof, err, nbytes}. The epoll
twin (S4) slots in behind this surface when the linux target lands.
No timer registrations by design: request/keepalive eviction is
deadline math — deadline_in/expired/remaining_ms over std.time's
monotonic clock, with remaining_ms feeding wait's timeout. std.sx
barrel carries ; .ir snapshot regen is the usual mechanical
renumbering. examples/1632 pins idle timeout (and that it honors the
deadline), readable with fd/udata/nbytes, immediate writability on an
empty send buffer, and the eof flag on peer close; JIT + AOT.
32-byte darwin struct kevent, EVFILT_READ/WRITE/TIMER, EV_* flags, and
three thin helpers: kev_change (one registration entry), kq_apply
(immediate change, no drain), kq_wait (bounded drain, EINTR reissued,
negative timeout = forever). Off the std.sx barrel by design — the
OS-neutral facade over this and the epoll twin is std.event (S5).
examples/1631 pins zero-cost idle timeout, READ readiness with pending
byte count + udata round-trip, and EV_EOF on peer close; verified under
sx run AND sx build.
