feat: install pre-pacman ZFS snapshot hook on ZFS-root systems

archsetup took sanoid from install-archzfs but never ported the pre-pacman snapshot hook, so a ZFS-root install had no transaction-triggered rollback point — the working setup only existed as a hand-placed script on velox, lost on reinstall. Add configure_pre_pacman_snapshots(): a PreTransaction pacman hook plus a self-pruning script that keeps the 10 most recent pre-pacman snapshots (sanoid ignores them — they aren't autosnap_ names). It's gated to ZFS-root and runs late in boot_ux, so the hook doesn't fire during the install's own package operations and the first snapshot is the fresh system.

The script ships as scripts/zfs-pre-snapshot, made ZFS_PRE_* env-overridable so the pruning logic is unit-testable. Unit tests drive it against a fake zfs (creates a snapshot, prunes the oldest past KEEP, ignores non-pre-pacman snapshots, honors the lockfile interval, warns on failure); a Testinfra test asserts the hook and script land on a ZFS install; the orchestrator test pins the new boot_ux substep.

1 files changed, 14 insertions, 0 deletions

diff --git a/tests/zfs-pre-snapshot/fake-zfs b/tests/zfs-pre-snapshot/fake-zfs
new file mode 100755
index 0000000..508c0f3
--- /dev/null
+++ b/tests/zfs-pre-snapshot/fake-zfs
@@ -0,0 +1,14 @@
+#!/bin/sh
+# Fake zfs for the zfs-pre-snapshot unit test. `snapshot` and `destroy` are
+# logged (FAKE_ZFS_LOG); `list` prints a fixture snapshot set (FAKE_ZFS_SNAPSHOTS).
+# Set FAKE_ZFS_SNAPSHOT_FAIL to make snapshot creation fail.
+case "$1" in
+    snapshot)
+        [ -n "$FAKE_ZFS_SNAPSHOT_FAIL" ] && exit 1
+        echo "snapshot $2" >> "$FAKE_ZFS_LOG"; exit 0 ;;
+    destroy)
+        echo "destroy $2" >> "$FAKE_ZFS_LOG"; exit 0 ;;
+    list)
+        cat "$FAKE_ZFS_SNAPSHOTS" 2>/dev/null; exit 0 ;;
+esac
+exit 0