Well as usual staring at a reiteration of your "clue" was of no use to me.
I figured it out in the middle of my sandwich. I think it is mostly my inability to recognize a kind of error I just don't usually make... and a perfect case of where seeking answers on a real computer would be misleading.
In any case, as mentioned a compiler warning is generated on the Arduino, so no one has any excuse to wonder why it doesn't work.
I think if arduino.h was explicitly included it might reduce my objection an iota or two. Just one more thing under the hood meant to make thing easier which doesn't always necessarily.
a7