It's part of the gold tier in the Pedestrian Working Group's schema, which is information they expect to be used by advanced routers. I'm just trying to be as complete as I can! Here's a keynote about the schema:
https://urbanists.video/w/xgsfWf98w4QLEbLKCZisH4

Ah, I see! Worth reverting, then.
This does make me wonder what the approach is to tag the width of footways, since really the width is the entire pedestrian area.

I added a bridge structure, what do you think of that solution?

Hmm, I suppose that can be important if there are height restrictions for the highway under the bridge. I'm just always nervous that navigation apps will continue trying to use a route even if the way is tagged as access=no. Is it possible to mark a bridge structure without there being a highway way on it?

That's seems like a safe bet, it would be unusual for a Little Free Library to be inside a building!

Very nice! I should probably stop trying to answer that question in the winter, since evidence of outdoor seating often disappears. 😅

Got it, I'll make that change!
I also noticed that currently the business is attached to the area of the building, but my understanding is that businesses are usually created as nodes placed on their building. Do you think that is worth changing as well?