I'm very confused about what's going on. In fact as far as I can tell those specific bugs were fixed.

https://bugs.php.net/bug.php?id=78876 marks the OOM bug as closed and fixed in 2020.

It seems the AI exploration was able to find variants of those bugs that were not fixed rather than exactly those bugs themselves?

That report describes sending a 2^31 length filename, which is cast to a negative number, which leads to asking erealloc() to allocate a very large buffer, which fails, which leads to the symptoms of the bug we're discussing today (mid-request allocation failure becomes a partially initialised request)

The fix at the time wasn't to do proper cleanup on eralloc() failure, it was merely to avoid filename length being cast to a negative number.

Or perhaps the fixes were not complete, and only addressed a specific test case instead of resolving the wider issue.