bcachefs on RHEL 10.2: The Kernel That Said No

A few months ago I bullied RHEL onto a ZFS root and it worked. This time I tried to get bcachefs running on RHEL 10, lost a whole evening to compile errors, and the kernel won. Here is the autopsy, plus what bcachefs actually is and why an out-of-tree filesystem and a conservative enterprise kernel are a terrible couple.