Re: btrfs vs bcachefs
>1. It cannot reliably report free space
What about `btrfs filesystem usage` or `btrfs fi df`
>2. Any attempt to write to a full Btrfs volume _will_ corrupt the volume.
Grok told me that "Modern Btrfs is designed to fail safely, not silently corrupt data. You may get write failures or read-only remounts, but not guaranteed corruption." Not sure if that's true.
>3. There is no working `fsck`. The repair tools do not work.
That seems to be true
On the other hand, you get snapshots, checksums for data integrity, compression, subvolumes and so on. So there's good reasons to want to use it instead of ext4.