btrfs compression not enabled on root filesystem as fstab suggests

### Describe the bug I'm not sure if this is a bug, or just an inconsistency between fstab and how the system actually mounts the root fs in a default installation. I have performed a fresh install of Bluefin (44). The `fstab` shows this: ``` UUID=9114f1cc-c55f-40f2-9e59-05d469b563a0 / btrfs subvol=root,compress=zstd:1,x-systemd.device-timeout=0,ro 0 0 UUID=82bf6ba9-7068-45d5-94fa-12b0f2f0da72 /boot ext4 defaults 1 2 UUID=BA8E-CA42 /boot/efi vfat umask=0077,shortname=winnt 0 2 UUID=9114f1cc-c55f-40f2-9e59-05d469b563a0 /home btrfs subvol=home,compress=zstd:1,x-systemd.device-timeout=0 0 0 UUID=9114f1cc-c55f-40f2-9e59-05d469b563a0 /var btrfs subvol=var,compress=zstd:1,x-systemd.device-timeout=0 0 0 ``` Clearly it's the intention for transparent zstd compression to be enabled. _But_, the root filesystem doesn't appear to be mounted using those arguments: ``` paul@x9 ~> mount | grep btrfs | head -n1 /dev/mapper/luks-dd70e3aa-f93e-4b5e-beb2-744665db3445 on /etc type btrfs (rw,relatime,seclabel,ssd,discard=async,space_cache=v2,subvolid=256,subvol=/root) ``` To actually get compression, it needs to be set as a kernel argument, I think. I can do that manually with `sudo rpm-ostree kargs --edit`, adding `compress=zstd:1` to the `rootflags`. After rebooting I get: ``` paul@x9 ~> mount | grep btrfs | head -n1 /dev/mapper/luks-dd70e3aa-f93e-4b5e-beb2-744665db3445 on /etc type btrfs (rw,relatime,seclabel,compress=zstd:1,ssd,discard=async,space_cache=v2,subvolid=256,subvol=/root) ``` --- This impacts all subvolumes on the root btrfs filesystem as flags for compression are taken from the first mount of the FS only. ### What did you expect to happen? I'm not sure what Bluefin developers expect, but it looks like someone expects btrfs transparent compression to be enabled on the root filesystem. In practice it isn't by default. ### Output of `bootc status` ```shell paul@x9 ~> sudo bootc status ● Booted image: ghcr.io/ublue-os/bluefin-dx:stable Digest: sha256:68cf991145523cde87e405fb2824e7bb4fe46f4beb234db503f6a647d0c86208 (amd64) Version: 44.20260519 (2026-05-19T01:56:18Z) Rollback image: ghcr.io/ublue-os/bluefin-dx:stable Digest: sha256:68cf991145523cde87e405fb2824e7bb4fe46f4beb234db503f6a647d0c86208 (amd64) Version: 44.20260519 (2026-05-19T01:56:18Z) ``` ### Output of `groups` ```shell ``` ### Extra information or context _No response_