terra btrfs

hosts/terra/disk-config.nix

@@ -1,10 +1,18 @@
 { ... }:
 
-# Declarative OS-disk layout (disko). UEFI: GPT with an ESP + ext4 root.
+# Declarative OS-disk layout (disko). UEFI: GPT with an ESP + btrfs root.
 # disko both PARTITIONS/FORMATS this disk and generates the NixOS
 # `fileSystems.*` entries, so hardware-configuration.nix must NOT define
 # fileSystems for "/" or "/boot".
 #
+# ⚠️  Root is btrfs (was ext4): the disk previously held a CachyOS btrfs root,
+#     and disko's `mkfs` create step SKIPS formatting when `blkid` still
+#     detects a filesystem signature on the freshly-cut partition. A stale
+#     btrfs superblock survives `wipefs`+repartition inside the new root
+#     partition's range, so an ext4 root got skipped and `mount -t ext4`
+#     then failed on the leftover btrfs bytes ("bad superblock"). btrfs's
+#     create runs `mkfs.btrfs -f`, which reformats past any stale signature.
+#
 # ⚠️  This disk is WIPED on install. This is the Kingston SA400 SSD that
 #     currently holds CachyOS (btrfs root+subvols on sdb2, ESP on sdb1).
 #     The dev-data disks (sdc ext4 /mnt/hdd_01, LVM vg_ssd /mnt/ssd_01) and the
@@ -31,8 +39,8 @@
         root = {
           size = "100%";
           content = {
-            type = "filesystem";
-            format = "ext4";
+            type = "btrfs";
+            extraArgs = [ "-f" ];
             mountpoint = "/";
           };
         };