**Feature summary** (what you would like to be able to do and where):
* on the Wikipedia iOS app, you can currently enter edit mode and attempt to publish an edit on a semi-protected page
* the warning that the edit cannot be saved (because the page is protected) happens only after you attempt to save your edit, which is super frustrating because you can put a bunch of time into an edit and then you're stuck because it can't be saved
* This is inconsistent with the mobile web and desktop behavior, where editing is prevented before you do the work of making changes to a protected page. On desktop Vector, the edit buttons are hidden completely and you only see View Source, which is also not very new editor friendly. The best experience is probably mweb, where you see the edit button with a lock icon and a toast error message is displayed (see screenshot). {F35338518}
**Benefits** (why should this be implemented?):