well I see, in my opinion repairing 1 block doesn't make sense, purely because
a) BTC node isn't guaranteed to be present
b) even if BTC node is present, how do you know it won't send the wrong information again
c) even if it sends the right information, you will need to download all the blocks after that blocks
anyway, for example in case a previously unseen commitment abc...123 was fixed by being "removed" from block 500000 (because it isn't there), all
the 500000+ blocks need to be inspected to confirm that abc...123 doesn't appear there again to "add it" (make it previously unseen in a later block).
d) so you can pretty much repair only errors that are fixed by "adding" commitments, and you will still need to fix up later blocks to remove from them
e) all of this makes it pretty narrow scoped as opposed to node operator simply copying over the "right" database to the node from a known good backup.
here is my final fix for the high severity problem. Only difference between the preliminary fix and this is the removal of the mutex commits_mutex locks+unlocks in the two cases (merkle_mine+merkle_unmine) where it's being held already and it would just cause a deadlock.
merkle.go https://pastebin.com/raw/SR2Y83Qttxlegs.go https://pastebin.com/raw/vgfRjNYFI was thinking more along the line of some unseen problem causing a corruption in the commits db, not a wrong input from the BTC. So the scenario would assume that, at one point, Haircomb did have a full, correct commits db file, and then something happened to cause one or more blocks to become corrupted. But you're right, it makes a lot more sense just to restore form a backup in this case.