ocaml: phase 3 'as' alias + 'when' guard in match (+6 tests, 295 total)

Pattern parser top wraps cons-pat with 'as ident' -> (:pas PAT NAME).
Match clause parser consumes optional 'when GUARD-EXPR' before -> and
emits (:case-when PAT GUARD BODY) instead of :case.

Eval: :pas matches inner pattern then binds the alias name; case-when
checks the guard after a successful match and falls through to the next
clause if the guard is false.

Or-patterns deferred — ambiguous with clause separator without
parens-only support.

lib/ocaml/test.sh

@@ -728,6 +728,20 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 1105)
 (eval "(ocaml-run-program \"let r = { x = 1; y = 2 };; r.x + r.y\")")
 
+;; ── as / when in match ─────────────────────────────────────────
+(epoch 1200)
+(eval "(ocaml-run \"match Some 5 with | Some x as p -> x | None -> 0\")")
+(epoch 1201)
+(eval "(ocaml-run \"match 5 with | n when n > 0 -> 1 | n when n < 0 -> -1 | _ -> 0\")")
+(epoch 1202)
+(eval "(ocaml-run \"match (-3) with | n when n > 0 -> 1 | n when n < 0 -> -1 | _ -> 0\")")
+(epoch 1203)
+(eval "(ocaml-run \"match 0 with | n when n > 0 -> 1 | n when n < 0 -> -1 | _ -> 0\")")
+(epoch 1204)
+(eval "(ocaml-run \"match (Some 7) with | None -> 0 | Some x when x > 5 -> x * 10 | Some x -> x\")")
+(epoch 1205)
+(eval "(ocaml-run \"match (Some 3) with | None -> 0 | Some x when x > 5 -> x * 10 | Some x -> x\")")
+
 EPOCHS
 
 OUTPUT=$(timeout 180 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -1153,6 +1167,14 @@ check 1103 "record string field"          '"Bob"'
 check 1104 "record int field"             '30'
 check 1105 "top-level record decl"        '3'
 
+# ── as / when in match ──────────────────────────────────────────
+check 1200 "Some x as p"                  '5'
+check 1201 "when sign +"                  '1'
+check 1202 "when sign -"                  '-1'
+check 1203 "when sign 0"                  '0'
+check 1204 "when guard fires"             '70'
+check 1205 "when guard skips"             '3'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "ok $PASS/$TOTAL OCaml-on-SX tests passed"