ocaml: phase 3 exception declarations (+4 tests, 304 total)

exception NAME [of TYPE] parses to (:exception-def NAME [ARG-SRC]).
Runtime is a no-op: raise/match already work on tagged ctor values, so
'exception E of int;; try raise (E 5) with | E n -> n' end-to-end with
zero new eval logic.

lib/ocaml/test.sh

@@ -754,6 +754,16 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 1304)
 (eval "(ocaml-run-program \"type shape = Circle of int | Square of int ;; match Circle 5 with | Circle r -> r | Square s -> s\")")
 
+;; ── exception declarations ────────────────────────────────────
+(epoch 1320)
+(eval "(ocaml-parse-program \"exception MyExn\")")
+(epoch 1321)
+(eval "(ocaml-parse-program \"exception MyExn of int\")")
+(epoch 1322)
+(eval "(ocaml-run-program \"exception E of int ;; try raise (E 5) with | E n -> n\")")
+(epoch 1323)
+(eval "(ocaml-run-program \"exception E of string ;; try raise (E \\\"oops\\\") with | E s -> s\")")
+
 EPOCHS
 
 OUTPUT=$(timeout 180 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -1194,6 +1204,12 @@ check 1302 "type-decl + match Red"        '1'
 check 1303 "type-decl + match Blue"       '3'
 check 1304 "type-decl + Circle r"         '5'
 
+# ── exception declarations ─────────────────────────────────────
+check 1320 "exception nullary"            '("exception-def" "MyExn")'
+check 1321 "exception arg"                '("exception-def" "MyExn"'
+check 1322 "raise+catch with arg"         '5'
+check 1323 "raise+catch string arg"       '"oops"'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "ok $PASS/$TOTAL OCaml-on-SX tests passed"