wcc/ww: under-length array-literal tail zero-fills

The unspecified tail of a short array literal repeated the last value
instead of zeroing — wwstage only (cstage already zeroes; the review's
both-stages reading didn't survive ground truth). Zero-fill the tail
per the zero-value semantics ruling. Review item #13.

selfhost/cmd/wwdump/main.combined.ww

@@ -42632,13 +42632,24 @@ fn emitarraylitbytes(c: *cgen, arrt: *tinfo, rhs: *node,
 	e = rhs.list;
 	let inrepeat: bool = false;
 	for (idx < alen) {
-		let v: u64 = last;
-		if (!inrepeat && e != nil) {
+		// #13: explicit elements fold normally; a `...` repeat replays the
+		// LAST value; the tail PAST the explicit elements (no `...`) is
+		// ZERO-filled. Pre-fix the default was `last`, so an under-length
+		// literal (`[4]u64 = [1, 2]`) repeated the last value into the tail
+		// instead of zero — cstage already zeroes (Hare: unspecified array
+		// elements are zeroed; the #16-task zero-value ruling); this aligns
+		// wwstage, a gate-blind cs!=ww divergence at the array-global path.
+		let v: u64 = 0u64;
+		if (inrepeat) {
+			v = last;
+		} else { if (e != nil) {
 			if (e.kind == nkind.N_FIELD) {
 				if (streq(e.str, "...")) {
 					inrepeat = true;
+					v = last;
 				} else {
 					e = e.next;
+					v = last;
 				};
 			} else {
 				let ev: *node = e;
@@ -42647,7 +42658,7 @@ fn emitarraylitbytes(c: *cgen, arrt: *tinfo, rhs: *node,
 				last = v;
 				e = e.next;
 			};
-		};
+		};};
 		let nb: u64 = v;
 		let bb: i32 = 0;
 		for (bb < esz) {