cgen: key the str/slice arg recognizers off the checker stamp

The wwstage nodeisstr/nodeisslice recognizers were name-keyed for
every non-local shape: an indirect fn-pointer callee ((*f)() — the
errnotest #59.5 divergence, streq receiving a shifted register file)
and module-global let/const idents (path.sepstr — union-widen pushes
zero-filled len/cap) both fell to false while cstage keys off the
checker stamp unconditionally. Both recognizers now fall back to the
stamped n.type_; push and pop sites share them, so the drain stays
balanced by construction. Graduates the #59.5 errnotest pin.

test/wcc/989_lib_byteid.c

@@ -157,8 +157,14 @@ static const struct ent ents[] = {
 	{ .fixture = "lib/encoding/base64/base64_test.ww",
 	  .mode = M_ID },
 	/* #59.4 hextest graduated to M_ID above (#22a reviewer fixes) */
+	/* #59.5 graduated: the wwstage nodeisstr/nodeisslice recognizers
+	 * fell to false for an indirect fn-pointer callee (`(*f)()`) and
+	 * for module-global let/const idents, so a 3-word str/slice value
+	 * pushed one word (or zero-filled its widen box) and cgcall
+	 * under-drained; both now fall back to the checker stamp. Runtime
+	 * pins: r595_indirect_call_str_arg, globalconst_{str,slice}_widen. */
 	{ .fixture = "lib/errors/errnotest.ww",
-	  .mode = M_DIVERGE, .cite = "#59.5" },
+	  .mode = M_ID, .cite = "#59.5 graduated by the stamp-keyed recognizers" },
 	/* #59.6 fmt graduated to M_ID above (#129 fix) */
 	/* #59.7 siphash graduated to M_ID above (#61 fix) */
 	{ .fixture = "lib/log/logtest.ww",