What are you trying to achieve?
Log/report libvips warnings when failOnError is flagged false.

Have you searched for similar feature requests?
Yes

What would you expect the API to look like?
Unsure

What alternatives have you considered?
Work around is to spawn sharp instance with failOnError flagged true, record any error message and then to try reprocess with failOnError flagged false.

Is there a sample image that helps explain?
I can provide if required.