set_nonblocking (C-variadic fcntl), errno via __error (darwin; C3
selects per-OS), and accept_nb/read_nb/write_nb returning a typed
SockErr — WouldBlock / Closed / Fault — so readiness-loop callers never
parse -1/errno pairs. EINTR retries internally; accept_nb skips
ECONNABORTED. Adds connect, shutdown, socketpair, AF_UNIX, SHUT_*.
examples/1630 pins the result algebra on a socketpair and a nonblocking
TCP listener (WouldBlock on empty backlog, accept after loopback
connect); verified under sx run AND sx build. The .ir snapshot regen is
mechanical: new std decls shift @str/@tag.str numbering and grow the
type table (179 -> 185).
The vendored amalgamation (3.53.2, public domain) plus the curated
bindings move from the distribution repo into the sx library:
'#import "vendors/sqlite/sqlite.sx"' gives any sx program SQLite
with no system dependency and no build flags — the bindings declare
the C as a named #import c unit (pinned defines + -O2), compiled
through the object cache and shadow-proof via unit-first resolution.
examples/1624 pins the version and a typed round trip in-suite.
