After some more in-depth debugging (still there, but mostly commented out) about why the negative message scan numbers are being hit and forward scan isn't working, but only for Ddoctest, I believe that I've found it's due to something having corrupted the pointers for that particular user. None of the other users have it, even if they switch to Ddoc and login the same way. Code that I know was ironclad back in the day has the bug, it's got to be a corrupted last message pointer for Ddoctest. So now I need to go about figuring how to fix that; good news is that the code isn't borked.
After some more in-depth debugging (still there, but mostly commented out) about why the negative message scan numbers are being hit and forward scan isn't working, but only for Ddoctest, I believe that I've found it's due to something having corrupted the pointers for that particular user. None of the other users have it, even if they switch to Ddoc and login the same way. Code that I know was ironclad back in the day has the bug, it's got to be a corrupted last message pointer for Ddoctest. So now I need to go about figuring how to fix that; good news is that the code isn't borked.