Normally when you visit a redirected MW page e.g. wp:Beatles
- the page displays a nifty #contentSub div with a helpful (Redirected from [[OldPage]]) redirectedfrom message.
- JS (mediawiki.action.view.redirect.js) changes the browser's location field to the URL of the redirected-to page.
Redirects to Flow boards don't do either, e.g. https://www.mediawiki.org/wiki/Talk:Flow_Portal silently shows the redirected-to Flow page with no indication except that the H1 title doesn't match the title in the URL.
Core's showRedirectFromHeader() in Article.php gives you this "for free", but Flow's View.php isn't an Article. Somehow the JsonSchema content type handles this correctly, see test redirect to schema on meta; maybe class WikitextContent is doing the work.