check: type the N_BIN operand of as in the wwstage

An enum OR-fold under `as` ((m.A|m.B) as u32) was never typed:
scruttype resolves IDENT/DOT only, and the post-order restamp then
re-derived the folded member literals as untyped_int. The unstamped
operand missed cgtypeassert's #27b enum-reinterpret gate and lowered
as a phantom tagged assert — unconditional exit 1 at runtime on the
wwstage leg. checkisas now types an N_BIN lhs and the N_BIN restamp
preserves an existing enum stamp. Graduates the #59.9 stattest pin.

test/wcc/989_lib_byteid.c

@@ -169,8 +169,13 @@ static const struct ent ents[] = {
 	/* #59.7 siphash graduated to M_ID above (#61 fix) */
 	{ .fixture = "lib/log/logtest.ww",
 	  .mode = M_DIVERGE, .cite = "#59.8" },
+	/* #59.9 graduated: the wwstage checker never typed an N_BIN operand
+	 * of `as`, so an enum OR-fold reached cgen unstamped and lowered as
+	 * a phantom tagged assert (unconditional exit 1). checkisas now
+	 * types the N_BIN lhs and the post-order restamp preserves the enum
+	 * stamp. Runtime pin: r599_enum_orfold_as. */
 	{ .fixture = "lib/os/stattest.ww",
-	  .mode = M_DIVERGE, .cite = "#59.9" },
+	  .mode = M_ID, .cite = "#59.9 graduated by the checkisas N_BIN stamp" },
 	/* #59.10 stoftest graduated to M_ID above (#62 fix) */
 	{ .fixture = "lib/ww/syntax/toktest.ww", .inc = "lib/ww",
 	  .mode = M_ID, .cite = "#59.11 graduated by #146 str==" },