Handle cache misses, render failures, and the language-unavailable case by falling back to the M1-defined secondary banner variant over whatever degraded content is available, never by silently serving an empty page or the default MediaWiki "this page does not exist" output.

A mainspace URL that a reader reached from a link must always produce a legible response, even when the underlying abstract content is temporarily unavailable; failing cleanly is strictly more important in M2 than it was in M1, because the reader here did not navigate to a special page and will not necessarily understand that the content is cross-wiki at all if the failure mode is an empty page.