Whatever `btrfs` did, it did a proper job of it.

10 hours later and `btrfsck --repair` still grinding away. Yes I took a snapshot of the disk before making changes.

Still going… seeing a lot of messages like this:

```
ref mismatch on [35132342272 8192] extent item 1, found 0
data extent[35132342272, 8192] bytenr mimsmatch, extent item bytenr 35132342272 file item bytenr 0
data extent[35132342272, 8192] referencer count mismatch (root 256 owner 227508 offset 149012480) wanted 1 have 0
backpointer mismatch on [35132342272 8192]
owner ref check failed [35132342272 8192]
repair deleting extent record: key [35132342272,168,8192]
Repaired extent references for 35132342272
ref mismatch on [35132350464 8192] extent item 1, found 0
data extent[35132350464, 8192] bytenr mimsmatch, extent item bytenr 35132350464 file item bytenr 0
data extent[35132350464, 8192] referencer count mismatch (root 256 owner 227508 offset 149020672) wanted 1 have 0
backpointer mismatch on [35132350464 8192]
owner ref check failed [35132350464 8192]
repair deleting extent record: key [35132350464,168,8192]
Repaired extent references for 35132350464
```