Swap: skip when already active, btrfs-aware creation (fallocate fails on btrfs)

arch-setup.sh

@@ -335,15 +335,23 @@ fi
 
 step "Swap file"
 
-if [ ! -f /swapfile ]; then
-    fallocate -l 2G /swapfile
-    chmod 600 /swapfile
-    mkswap /swapfile
+if swapon --show --noheadings 2>/dev/null | grep -q .; then
+    warn "Swap already active — skipping:"
+    swapon --show
+elif [ -f /swapfile ]; then
+    warn "Swap file already exists — skipping"
+else
+    # fallocate swapfiles fail on btrfs (needs NOCOW) — use the proper tool
+    if [ "$(findmnt -n -o FSTYPE /)" = "btrfs" ]; then
+        btrfs filesystem mkswapfile --size 2g /swapfile
+    else
+        dd if=/dev/zero of=/swapfile bs=1M count=2048 status=none
+        chmod 600 /swapfile
+        mkswap /swapfile
+    fi
     swapon /swapfile
     grep -q '/swapfile' /etc/fstab || echo '/swapfile none swap sw 0 0' >> /etc/fstab
     log "2GB swap created and enabled"
-else
-    warn "Swap file already exists — skipping"
 fi
 
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