ocaml: phase 6 Stack + Queue modules (+5 tests, 430 total)

Stack: ref-holding-list LIFO. push/pop/top/length/is_empty/clear.
Queue: two-list (front, back) amortised O(1) queue. push/pop/length/
is_empty/clear. Both in OCaml syntax in runtime.sx.

lib/ocaml/test.sh

@@ -1052,6 +1052,18 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 3502)
 (eval "(ocaml-run-program \"let b = Buffer.create 16 ;; Buffer.add_string b \\\"x\\\" ;; Buffer.clear b ;; Buffer.contents b\")")
 
+;; ── Stack + Queue modules ─────────────────────────────────────
+(epoch 3600)
+(eval "(ocaml-run-program \"let s = Stack.create () ;; Stack.push 1 s ;; Stack.push 2 s ;; Stack.push 3 s ;; Stack.pop s\")")
+(epoch 3601)
+(eval "(ocaml-run-program \"let s = Stack.create () ;; Stack.push 1 s ;; Stack.push 2 s ;; Stack.length s\")")
+(epoch 3602)
+(eval "(ocaml-run-program \"let s = Stack.create () ;; Stack.push 1 s ;; Stack.top s\")")
+(epoch 3603)
+(eval "(ocaml-run-program \"let q = Queue.create () ;; Queue.push 1 q ;; Queue.push 2 q ;; Queue.push 3 q ;; Queue.pop q\")")
+(epoch 3604)
+(eval "(ocaml-run-program \"let q = Queue.create () ;; Queue.push 1 q ;; Queue.push 2 q ;; Queue.length q\")")
+
 EPOCHS
 
 OUTPUT=$(timeout 180 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -1665,6 +1677,13 @@ check 3500 "Buffer concat 'Hello, World'" '"Hello, World"'
 check 3501 "Buffer.length 3"              '3'
 check 3502 "Buffer.clear empties"         '""'
 
+# ── Stack + Queue ──────────────────────────────────────────────
+check 3600 "Stack.pop LIFO"               '3'
+check 3601 "Stack.length"                 '2'
+check 3602 "Stack.top"                    '1'
+check 3603 "Queue.pop FIFO"               '1'
+check 3604 "Queue.length"                 '2'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "ok $PASS/$TOTAL OCaml-on-SX tests passed"