try the shared inbox for update deliveries

activity.go

@@ -1366,7 +1366,13 @@ func honkworldwide(user *WhatAbout, honk *Honk) {
 			}
 		}
 		for _, f := range getbacktracks(honk.XID) {
-			rcpts[f] = true
+			var box *Box
+			ok := boxofboxes.Get(f, &box)
+			if ok && box.Shared != "" {
+				rcpts["%"+box.Shared] = true
+			} else {
+				rcpts[f] = true
+			}
 		}
 	}
 	for a := range rcpts {