feat(install): add pre-flight environment and disk-target validation

archangel went straight from filesystem selection into a destructive install behind only a root check and a ZFS module load. A missing tool, a BIOS boot, a too-small or in-use disk, or a dead network surfaced as a confusing abort partway through, sometimes after partitioning had already run.

Two gates now fail fast. validate_environment runs after filesystem selection, before any disk is touched: it confirms UEFI boot mode and that every required command is present, with the list coming from a new required_commands helper built like pacstrap_packages. validate_install_targets runs after disk selection, before the first wipe: it refuses a target that's mounted, holds active swap, or belongs to an imported pool or md array, rejects disks under 20 GB, and confirms a mirror is reachable via DNS plus a TCP probe (no ICMP, since some networks drop it).

I folded the install_failure_cleanup hardening into the same change. It now falls back to lazy unmounts, so a pacstrap-interrupted target with busy bind mounts still releases the pool and unmounts the EFI partition. Without that, the disk-in-use guard would block the very retry the cleanup exists to enable. "Re-run to retry" only holds if the disk is genuinely freed first.

The 20 GB floor is decimal on purpose. It reads as the natural minimum and clears a 20 GiB disk image with headroom instead of sitting on the boundary.

1 files changed, 48 insertions, 0 deletions

diff --git a/tests/unit/test_common.bats b/tests/unit/test_common.bats
index 8ce7280..a639a4e 100644
--- a/tests/unit/test_common.bats
+++ b/tests/unit/test_common.bats
@@ -520,3 +520,51 @@ Boot0001* ZFSBootMenu"
     grep -qF 'HOOKS=(base udev)' "$f"
     rm -f "$f"
 }
+
+#############################
+# required_commands
+#############################
+
+@test "required_commands zfs includes zpool and zfs" {
+    run required_commands zfs
+    [ "$status" -eq 0 ]
+    [[ "$output" == *"zpool"* ]]
+    [[ "$output" == *"zfs"* ]]
+}
+
+@test "required_commands btrfs includes mkfs.btrfs and grub-install" {
+    run required_commands btrfs
+    [ "$status" -eq 0 ]
+    [[ "$output" == *"mkfs.btrfs"* ]]
+    [[ "$output" == *"grub-install"* ]]
+}
+
+@test "required_commands zfs excludes Btrfs-specific commands" {
+    run required_commands zfs
+    [ "$status" -eq 0 ]
+    [[ "$output" != *"mkfs.btrfs"* ]]
+    [[ "$output" != *"grub-install"* ]]
+}
+
+@test "required_commands btrfs excludes the zpool command" {
+    run required_commands btrfs
+    [ "$status" -eq 0 ]
+    [[ "$output" != *"zpool"* ]]
+}
+
+@test "required_commands includes partitioning + pacstrap commands for both filesystems" {
+    for fs in zfs btrfs; do
+        run required_commands "$fs"
+        [ "$status" -eq 0 ]
+        [[ "$output" == *"sgdisk"* ]]
+        [[ "$output" == *"wipefs"* ]]
+        [[ "$output" == *"partprobe"* ]]
+        [[ "$output" == *"mkfs.fat"* ]]
+        [[ "$output" == *"pacstrap"* ]]
+    done
+}
+
+@test "required_commands unknown filesystem returns 1" {
+    run required_commands ext4
+    [ "$status" -eq 1 ]
+}