Description
Celestia node would benefit from knowing about headers that are being pruned from the store. If any header gets deleted, the user can then react and delete user-specific data that the header is proving/pointing to.
In case of cel node, the callback will delete the sample or block data. Then, once a node starts and identifies the proper Tail, it will delete all the block data along with header pruning. This ensures that before Pruner even starts, Tail is already on par with Pruner's state, and all the block data before Tail is removed. This follows the CIP, where the storage pruning window can't be larger than the header pruning window.
If the Tail is absolute on the other hand, the Pruner still kicks in to prune data, allowing the case for HPW > SPW.