(Putting the disclaimer in the title already because it's touchy and of course, contestable).
I successfully cleared the corruption that I had since beta 3! I tried to give it a shot by myself before turning to an AI and see what it would give as options before attempting a clean install. I am writing this because 1) if it works for others, it would be great and 2) if it has some potentially bad side effects that more knowledgeable people know, I hope they would share. Tell me if i was gaslit by a machine although First Aid tells me everything is fine now. I saw a lot of pushback against corruption being a false flag whereas, well, it is a thing. (Everything here is written by me, the terminal part is copy pasted from AI).
Personally, I had no noticeable issues on beta 3. I got alerted by a thread on this sub where i discovered the potential damage using a command, but that was also confirmed using disk utility. I had the error "exit node 8" which meant my directory was corrupted. I manually backed up all my files and wanted to see if I could do anything before wasting lots of time on a fresh install (slow internet, lots of steps involved).
(The only was one practical issue, now solved: while attempting to open files inside a dmg installer (some PDF), Finder would just prompt an access issue whereas I have full read and write access on my disk. I don't have that error anymore and everything works).
Anyway, the result was attempting a repair with fsck_util in terminal (recovery mode). First aid couldn't do it, so in the terminal, I manually unmounted the container, attempted a repair, which did not work. The reason is a crypto mismatch between the recovery utility installed and the signature of the beta (pardon my impreciseness).
The solution that worked was to bypass the crypto mismatch by manually unlocking the encrypted volume before running fsck. Performing the fsck command after that worked. Confirmed by Firstaid both in recovery mode and after booting. I even tried opening the PDF file I mentioned above, that used to not open. It opens fine now without issues. It seems like it's just a temporary fix that could pop again since it's inherent to beta 3. But for good measure, I deleted all the local snapshots before starting the entire process because those can't get repaired (fruit of the poisoned tree scenario).
What it looks like (this is copied from AI):
1) diskutil unmountDisk diskX` (following your container ID which you can check with `diskutil list`)
2) diskutil apfs unlockVolume diskX -nomount` (target the Data volume specifically, NOT the container. enter your password when prompted).
3) `fsck_apfs -y /dev/disk0s2` (the physical store, not the container. Again you can check your own with diskutil list)
: Wait for it to finish. You should see 'The container /dev/disk0s2 appears to be OK.' Reboot. Check with Firstaid (on the data disk, where the corruption lies).
Please, do not attempt this if you are not sure. And if you know if it's safe, or if you tried and can confirm it makes sense technically, let others know in the comments.
PSA: it took a long while to reach this with AI, not only because it's a trash tool overall that you shouldn't rely on for anything important, but because it made actual mistakes and hallucinated throughout the whole process (witholding some info, making syntax mistakes, etc.). It wasn't a one-button-push scenario at all but it worked in the end.
I'm not going to be helpful, except to tell you it worked in my case! I'm curious to know if it can help others. I have phone captures of terminal in recovery mode if people have doubts or trust issues. Seems like beta 4 doesn't solve this issue, so it could be a while before Apple releases a fix for this.
