Aug 8, 2021

Step 5 is a block reorg, and that is the source of block notifications. When a header is added to the candidate chain (reorged), that chain is now stronger than the confirmed chain. That triggers a header (reorg) notification. There is actually a third (partial tree) data structure that maintains branches until they are stronger than the persistent candidate chain. The header reorg occurs from the header tree to the candidate chain. The header tree has a configurable maximum depth constraint.