ocaml: phase 6 List.sort + compare (+7 tests, 339 total)

compare is a host builtin returning -1/0/1 (Stdlib.compare semantics)
deferred to host SX </>. List.sort is insertion-sort in OCaml: O(n²)
but works correctly. List.stable_sort = sort.

Tested: ascending int sort, descending via custom comparator (b - a),
empty list, string sort.

plans/ocaml-on-sx.md

@@ -242,8 +242,8 @@ SX CEK evaluator (both JS and OCaml hosts)
 - [~] `List`: `map`, `filter`, `fold_left`, `fold_right`, `length`, `rev`,
       `append`, `iter`, `for_all`, `exists`, `mem`, `nth`, `hd`, `tl`,
       `rev_append`, `concat`/`flatten`, `init`, `iteri`, `mapi`, `find`,
-      `find_opt`, `assoc`, `assoc_opt`, `partition`. _(Pending:
-      sort/stable_sort, combine, split.)_
+      `find_opt`, `assoc`, `assoc_opt`, `partition`, `sort`,
+      `stable_sort` (insertion sort, O(n²)). _(Pending: combine, split.)_
 - [~] `Option`: `map`, `bind`, `value`, `get`, `is_none`, `is_some`,
       `iter`, `fold`, `to_list`. _(Pending: join/to_result.)_
 - [~] `Result`: `map`, `bind`, `is_ok`, `is_error`, `get_ok`,
@@ -365,6 +365,11 @@ the "mother tongue" closure: OCaml → SX → OCaml. This means:
 
 _Newest first._
 
+- 2026-05-08 Phase 6 — `List.sort` + polymorphic `compare` (+7 tests,
+  339 total). `compare` is a host primitive that returns -1/0/1 like
+  Stdlib.compare, defers to host SX `<`/`>`. `List.sort` is implemented
+  in OCaml as insertion sort: O(n²) but correct, and passes all tests
+  including descending custom comparator and string sort.
 - 2026-05-08 Phase 6 — `Hashtbl` (+6 tests, 332 total). Backing store is
   a one-element list cell holding a SX dict; keys are coerced to
   strings via `str` so any value type can serve as a key. API: create,