Where does Panther save its SAFE_OS minidumps?

I'm trying to debug a (likely) driver crash during a Windows 10 feature update ("extend" code 0x2000D). The log (abbreviated since it's on a different machine) says

FatalError [0x090001] PANTHR Exception (code 0xE06D7363: <unknown>) occurred at ...
Minidump attached (69263 bytes) to diagerr.xml and X:\Windows\Panther\UnattendedGC\mndE39.diagerr.mdmp.

I can't see nothing attached to any diagerr.xml, nor do I have an X: drive mounted on this machine. Nor is there any UnattendedGC dir anywhere on the machine.

There's nothing in %WINDIR%\Panther or in %WINDIR%\Minidump. So where does Panther actually save those (SAFE_OS phase) minidumps??

I'm guessing the answer is "nowhere" since the docs say

Because you are creating a new installation, the hard drive is not initially available, so Windows Setup writes logs into memory, specifically in a Windows PE session (X:\Windows). After the hard drive is formatted, Setup continues logging directly onto the new hard drive (C:\Windows). Log files created during the Windows PE session are temporary.

So X: seems to be a RAM drive that doesn't get copied somewhere else.