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).
All units share one link namespace (per-unit isolation is PLAN-C C3.2,
deferred), so a symbol defined by two units previously died inside the
JIT dylib link or the AOT link with raw linker spew. The clang shim
gains sx_clang_object_exported_symbols (llvm::object scan: defined +
global, format-specific excluded) and compileCToObjects cross-checks
every unit object — collisions name both source files. Scan failures
are non-fatal; the linker remains the backstop. Covers JIT and native
AOT; the emcc path still relies on wasm-ld's own error.
