Adds the tuple-keyed list family to lib/erlang/lists-ext.sx: act on
first match, key compare via == (er-equal?), non-tuples/short tuples
pass through. keysort/2 reuses the stable merge sort + full term
order. keytake/3 returns {value, Tuple, Rest} | false. All seven
registered through the er-register-builtin-bifs! wrapper so they
survive mid-run registry resets. lists_ext suite 17 -> 38.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
New lib/erlang/lists-ext.sx (loaded after runtime.sx): stable merge
sort over an SX-list bridge. sort/1 and usort/1 use full Erlang term
order via a self-contained er-ext-lt? (deep tuple/list compare that
the shared er-lt? lacks); sort/2 takes a fun(A,B)->bool comparator.
Registration wraps er-register-builtin-bifs! so the BIFs survive the
mid-run registry resets done by tests/runtime.sx.
Roadmap is saturated within this loop's scope; this is forever-loop
stdlib hardening. New file forced by the broken sx-tree write tools
in this worktree (see Blockers) — authored via Write + sx_validate.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
