If an operation fails during boot, the (Abstract)OperationContext reports that to the BootErrorCollector.
But it's possible for non-boot operations to execute during boot. These shouldn't be external requests (which get rejected before they get to the point of running with an OperationContext) but java agents run in-vm and can invoke operations. I believe Dynatrace may do that kind of thing.
We should try and distinguish the OperationContexts that are actually executing the boot steps from those that are just running during boot.
Whoever works on this needs to fully understand boot and the various types of operation contexts, including understanding how parallel boot works.