I suspect this is a regression

A regression from what? Do you have JOSM running on Android that used to work but now doesn't?

From the button not being displayed...

I assumed we wanted to display the edit button now. There were other pull requests implementing that, like #4839

edit on mobile version is a great idea, but it does not really make sense without links to mobile editors

edit on mobile version is a great idea, but it does not really make sense without links to mobile editors

It doesn't really need links, the JOSM RC interface is trivial to implement for any Android app, it is just an issue with the way the rails-ports generates the URL.

See #1478

PS: I'm not naive enough to assume that this will happen in any form, naturally everybody will want their own link for marketing purposes.

Would #1478 work also when user has no got any relevant app installed yet?

Maybe I misunderstood how it works but AFAIK not.

PS: I'm not naive enough to assume that this will happen in any form, naturally everybody will want their own link for marketing purposes.

I would prefer edit menu linking on Android to Vespucci and EveryDoor (or EveryDoor only) over the current state.

Would #1478 work also when user has no got any relevant app installed yet?

As is no, but you could show a popup or similar if nothing was installed (just as it now asks you to start JOSM on desktop), potentially you could offer to directly install an app, but that all gets kind of complicated in more than one way.

The good thing is that you wouldn't have to explicitly start the app once installed.

edit on mobile version is a great idea, but it does not really make sense without links to mobile editors

Does enabling iD still counts as "not really making sense"?