ocaml: phase 5 HM def-mut + def-rec-mut at top level (+3 tests, 454 total)

ocaml-type-of-program now handles :def-mut (sequential generalize) and
:def-rec-mut (pre-bind tvs, infer rhs, unify, generalize all, infer
body — same algorithm as the inline let-rec-mut version).

Mutual top-level recursion now type-checks:
  let rec even n = ... and odd n = ...;; even 10           : Bool
  let rec map f xs = ... and length lst = ...;; map :
                              ('a -> 'b) -> 'a list -> 'b list

lib/ocaml/test.sh

@@ -1116,6 +1116,14 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 4103)
 (eval "(ocaml-run \"let r = { x = 1; y = 2 } in r.x <- r.y * 10; r.x\")")
 
+;; ── HM top-level def-mut / def-rec-mut ────────────────────────
+(epoch 4200)
+(eval "(ocaml-type-of-program \"let x = 1 and y = 2;; x + y\")")
+(epoch 4201)
+(eval "(ocaml-type-of-program \"let rec even n = if n = 0 then true else odd (n - 1) and odd n = if n = 0 then false else even (n - 1);; even 10\")")
+(epoch 4202)
+(eval "(ocaml-type-of-program \"let rec map f xs = match xs with | [] -> [] | h :: t -> f h :: map f t and length lst = match lst with | [] -> 0 | _ :: t -> 1 + length t;; map\")")
+
 EPOCHS
 
 OUTPUT=$(timeout 180 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -1767,6 +1775,11 @@ check 4101 "for-loop accum r.x"           '15'
 check 4102 "r.name <- str"                '"Alice"'
 check 4103 "r.x <- r.y * 10"              '20'
 
+# ── HM top-level def-mut / def-rec-mut ─────────────────────────
+check 4200 "let-mut x+y"                  '"Int"'
+check 4201 "let-rec-mut even 10"          '"Bool"'
+check 4202 "let-rec-mut map+length"       'list -> '
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "ok $PASS/$TOTAL OCaml-on-SX tests passed"