Add snapshot retention with automatic pruning

Implements hybrid retention policy:
- Always keep 20 most recent snapshots
- Delete snapshots beyond #20 only if older than 180 days
- Genesis snapshot is always protected

Features:
- zfs-snap-prune script with --dry-run, --test, --verbose modes
- Comprehensive test suite (22 tests)
- Runs automatically after pacman operations
- Daily systemd timer for cleanup
- Regenerates GRUB menu after pruning

This prevents unbounded snapshot growth while preserving
recent history and the genesis snapshot.

1 files changed, 7 insertions, 0 deletions

diff --git a/build.sh b/build.sh
index cf5c086..67542ec 100755
--- a/build.sh
+++ b/build.sh
@@ -187,6 +187,10 @@ mkdir -p "$PROFILE_DIR/airootfs/usr/local/share/grub-zfs-snap"
 cp "$CUSTOM_DIR/40_zfs_snapshots" "$PROFILE_DIR/airootfs/usr/local/share/grub-zfs-snap/"
 cp "$CUSTOM_DIR/zz-grub-zfs-snap.hook" "$PROFILE_DIR/airootfs/usr/local/share/grub-zfs-snap/"
 
+# Copy zfs-snap-prune for snapshot retention
+info "Copying zfs-snap-prune..."
+cp "$CUSTOM_DIR/zfs-snap-prune" "$PROFILE_DIR/airootfs/usr/local/bin/"
+
 # Copy example config for unattended installs
 mkdir -p "$PROFILE_DIR/airootfs/root"
 cp "$CUSTOM_DIR/install-archzfs.conf.example" "$PROFILE_DIR/airootfs/root/"
@@ -207,6 +211,9 @@ if grep -q "file_permissions=" "$PROFILE_DIR/profiledef.sh"; then
         /)/ i\  ["/usr/local/bin/grub-zfs-snap"]="0:0:755"
     }' "$PROFILE_DIR/profiledef.sh"
     sed -i '/^file_permissions=(/,/)/ {
+        /)/ i\  ["/usr/local/bin/zfs-snap-prune"]="0:0:755"
+    }' "$PROFILE_DIR/profiledef.sh"
+    sed -i '/^file_permissions=(/,/)/ {
         /)/ i\  ["/etc/shadow"]="0:0:400"
     }' "$PROFILE_DIR/profiledef.sh"
 fi