We should display and collect information on the book creation failures, so that the users can act on them either by working around them or by reporting the most important and recurring failures. Statistics on the logs will also allow us to monitor the trend and gauge whether things are getting any better/worse (logging success would help monitor the usage trends as well).

Currently, the many reports on "Rendering process died with non zero code: 1" are hard to debug or work around, because they require someone to install OCG locally and test the wikitext against it.

Collection already has some log channels, which are enabled on Wikimedia wikis (6c8d2d4b (C. Scott Ananian 2014-10-22 11:52:05 -0400 4242) 'collection' => "udp://$wmfUdp2logDest/collection", // -cscott for bug 71675):

RenderingAPI.php
305:                    wfDebugLog( 'collection', "Request to $serveURL resulted in error" );
329:                            wfDebugLog( 'collection', "Server returned bogus data: $data" );
333:                            wfDebugLog( 'collection', "Server returned error: {$this->getError()}" );

It's possible that additional logging is needed and/or that some conversion to other logging systems is desired.

To be clear, it would be nice if output such as https://phabricator.wikimedia.org/T85668#1051805 was relayed to the user.