ocaml: phase 6 List.combine/split/iter2/fold_left2/map2 (+4, 367 total)

Mechanical pair-walk OCaml implementations. failwith on length
mismatch matches Stdlib semantics. List module now covers 30+
functions.

lib/ocaml/test.sh

@@ -900,6 +900,16 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 2105)
 (eval "(ocaml-type-of-program \"let rec fact n = if n = 0 then 1 else n * fact (n - 1);; fact 5\")")
 
+;; ── More List functions: combine/split/iter2/fold_left2/map2 ──
+(epoch 2200)
+(eval "(ocaml-run \"List.combine [1;2;3] [\\\"a\\\";\\\"b\\\";\\\"c\\\"]\")")
+(epoch 2201)
+(eval "(ocaml-run \"List.split [(1,\\\"a\\\");(2,\\\"b\\\")]\")")
+(epoch 2202)
+(eval "(ocaml-run \"List.fold_left2 (fun a b c -> a + b + c) 0 [1;2;3] [10;20;30]\")")
+(epoch 2203)
+(eval "(ocaml-run \"List.map2 (fun a b -> a + b) [1;2;3] [10;20;30]\")")
+
 EPOCHS
 
 OUTPUT=$(timeout 180 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -1423,6 +1433,12 @@ check 2103 "shape -> Int"                 '"shape -> Int"'
 check 2104 "program x+y"                  '"Int"'
 check 2105 "program fact 5"               '"Int"'
 
+# ── More List functions ─────────────────────────────────────────
+check 2200 "List.combine"                 '("tuple" 3 "c")'
+check 2201 "List.split"                   '("tuple" (1 2) ("a" "b"))'
+check 2202 "List.fold_left2"              '66'
+check 2203 "List.map2"                    '(11 22 33)'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "ok $PASS/$TOTAL OCaml-on-SX tests passed"