ocaml: phase 2 for/while loops (+5 tests, 194 total)

Parser: for i = lo to|downto hi do body done, while cond do body done.
AST: (:for NAME LO HI :ascend|:descend BODY) and (:while COND BODY).
Eval re-binds the loop var per iteration; both forms evaluate to unit.

lib/ocaml/test.sh

@@ -495,6 +495,18 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 605)
 (eval "(ocaml-run \"let count = ref 0 in let rec loop n = if n = 0 then !count else (count := !count + n; loop (n - 1)) in loop 5\")")
 
+;; ── for / while loops ──────────────────────────────────────────
+(epoch 620)
+(eval "(ocaml-run \"let s = ref 0 in for i = 1 to 5 do s := !s + i done; !s\")")
+(epoch 621)
+(eval "(ocaml-run \"let s = ref 0 in for i = 5 downto 1 do s := !s + i done; !s\")")
+(epoch 622)
+(eval "(ocaml-run \"let i = ref 0 in let s = ref 0 in while !i < 5 do i := !i + 1; s := !s + !i done; !s\")")
+(epoch 623)
+(eval "(ocaml-run \"let s = ref 0 in for i = 1 to 100 do s := !s + i done; !s\")")
+(epoch 624)
+(eval "(ocaml-run \"let p = ref 1 in for i = 1 to 5 do p := !p * i done; !p\")")
+
 EPOCHS
 
 OUTPUT=$(timeout 60 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -789,6 +801,13 @@ check 603 "ref captured by closure"      '115'
 check 604 "ref of string"                '"b"'
 check 605 "ref + recursion"              '15'
 
+# ── for / while ─────────────────────────────────────────────────
+check 620 "for 1..5 sum"                 '15'
+check 621 "for 5 downto 1 sum"           '15'
+check 622 "while loop"                   '15'
+check 623 "for 1..100 sum"               '5050'
+check 624 "for 1..5 product = 120"       '120'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "ok $PASS/$TOTAL OCaml-on-SX tests passed"