ocaml: phase 3 type declarations (+5 tests, 300 total)

Parser: type [PARAMS] NAME = | Ctor [of T1 [* T2]*] | ...
- PARAMS: optional 'a or ('a, 'b) tyvar list
- AST: (:type-def NAME PARAMS CTORS) with each CTOR (NAME ARG-SOURCES)
- Argument types captured as raw source strings (treated opaquely at
  runtime since ctor dispatch is dynamic)

Runtime is a no-op — constructors and pattern matching already work
dynamically. Phase 5 will use these decls to register ctor types for
HM checking.

lib/ocaml/test.sh

@@ -742,6 +742,18 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 1205)
 (eval "(ocaml-run \"match (Some 3) with | None -> 0 | Some x when x > 5 -> x * 10 | Some x -> x\")")
 
+;; ── type declarations (parser + runtime) ──────────────────────
+(epoch 1300)
+(eval "(ocaml-parse-program \"type color = Red | Green | Blue\")")
+(epoch 1301)
+(eval "(ocaml-parse-program \"type shape = Circle of int | Rect of int | Square of int\")")
+(epoch 1302)
+(eval "(ocaml-run-program \"type color = Red | Green | Blue ;; match Red with | Red -> 1 | Green -> 2 | Blue -> 3\")")
+(epoch 1303)
+(eval "(ocaml-run-program \"type color = Red | Green | Blue ;; match Blue with | Red -> 1 | Green -> 2 | Blue -> 3\")")
+(epoch 1304)
+(eval "(ocaml-run-program \"type shape = Circle of int | Square of int ;; match Circle 5 with | Circle r -> r | Square s -> s\")")
+
 EPOCHS
 
 OUTPUT=$(timeout 180 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -1175,6 +1187,13 @@ check 1203 "when sign 0"                  '0'
 check 1204 "when guard fires"             '70'
 check 1205 "when guard skips"             '3'
 
+# ── type declarations ───────────────────────────────────────────
+check 1300 "type color enum"              '("type-def" "color" () (("Red") ("Green") ("Blue")))'
+check 1301 "type shape with-args"         '("type-def" "shape"'
+check 1302 "type-decl + match Red"        '1'
+check 1303 "type-decl + match Blue"       '3'
+check 1304 "type-decl + Circle r"         '5'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "ok $PASS/$TOTAL OCaml-on-SX tests passed"