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, 43 insertions, 0 deletions

diff --git a/tests/unit/test_disk.bats b/tests/unit/test_disk.bats
index 1b3cfba..6bc6d8d 100644
--- a/tests/unit/test_disk.bats
+++ b/tests/unit/test_disk.bats
@@ -232,3 +232,46 @@ partition_disks_setup() {
     [[ " ${CALLS[*]} " != *"sgdisk"* ]]
     [[ " ${CALLS[*]} " != *"wipefs"* ]]
 }
+
+#############################
+# disk_meets_min_size / MIN_DISK_BYTES
+#############################
+
+@test "MIN_DISK_BYTES is 20 GB (decimal)" {
+    [ "$MIN_DISK_BYTES" -eq 20000000000 ]
+}
+
+@test "disk_meets_min_size: exactly the minimum passes" {
+    run disk_meets_min_size 20000000000
+    [ "$status" -eq 0 ]
+}
+
+@test "disk_meets_min_size: one byte under the minimum fails" {
+    run disk_meets_min_size 19999999999
+    [ "$status" -eq 1 ]
+}
+
+@test "disk_meets_min_size: a 20 GiB disk image clears the 20 GB floor" {
+    run disk_meets_min_size 21474836480
+    [ "$status" -eq 0 ]
+}
+
+@test "disk_meets_min_size: a large disk passes" {
+    run disk_meets_min_size 500107862016
+    [ "$status" -eq 0 ]
+}
+
+@test "disk_meets_min_size: zero fails" {
+    run disk_meets_min_size 0
+    [ "$status" -eq 1 ]
+}
+
+@test "disk_meets_min_size: non-numeric input fails" {
+    run disk_meets_min_size notanumber
+    [ "$status" -eq 1 ]
+}
+
+@test "disk_meets_min_size: empty input fails" {
+    run disk_meets_min_size ""
+    [ "$status" -eq 1 ]
+}