Follow up the T378827#10424041 request by @Stryn, there should be a simpler way to move Flow pages once it is switched to read-only mode. For posterity, here is what I did:
- Set wgFlowReadOnly to false for fiwiki at a mwdebug host
- From a privileged wiki account, perform the move
- Reset the change
Moving the page should be harmless, and sometimes necessary to facilitate late archiving (like in this case). Filling this for reference, if this is a super-rare usecase, we can use the process we have already.