I saw your description of "a cake conveying a message" as misrepresenting the claim by once again reducing it to being just "A cake. A piece of confection," and with the claim of `conveying a message not being validated by any court ruling.
However, the fact is that a cake with writing on it, as well as providing a special "wedding cake" sends a message. The Ireland court recognized the first, and invoked SCOTUS in recognizing a cake as conveying a particular message, with the acquitting factor in both cases being that it was the message itself that was the cause for the denial of service, irrespective of how/what the person was, though that was the reason the respective customers wanted the cake.
"The important message from the Masterpiece Cakeshop case is that there is a clear distinction between refusing to produce
a cake conveying a particular message, for any customer who wants such a cake, and refusing to produce a cake [conveying a particular message] for the particular customer who wants it because of that customer’s characteristics.”
"The bakery would have refused to supply this particular cake to anyone, whatever their personal characteristics." -
UK's top court: Refusing to make cake with 'Support Gay Marriage' slogan not discrimination