chore(ai,aquamarine): shrink the swapfile to 32G

disko creates the swapfile only when it formats the pool, so the live 96G files
keep their size until they are recreated with btrfs filesystem mkswapfile; that
frees 64G per host.

Assisted-by: DeepSeek Harness 0.2.0-rc.2 (deepseek-flash)

hosts/idols-ai/disko-fs.nix

@@ -112,10 +112,12 @@
                       "compress-force=zstd:1"
                     ];
                   };
-                  # Swap subvolume read-only; disko creates swapfile and adds swapDevices
+                  # Swap subvolume read-only; disko creates swapfile and adds swapDevices.
+                  # The swapfile is preallocated and never compressed (btrfs swapfile
+                  # requirements), so it consumes its full size on the pool.
                   "@swap" = {
                     mountpoint = "/swap";
-                    swap.swapfile.size = "96G";
+                    swap.swapfile.size = "32G";
                   };
                 };
               };

hosts/idols-aquamarine/README.md

@@ -39,7 +39,7 @@ defect that is, the supported ROCm versions, and the inference notes.
 ## Disk layout
 
 Declarative via [disko-fs.nix](./disko-fs.nix): ESP + LUKS (`aqua-luks`) + btrfs subvolumes (`@nix`,
-`@persistent`, `@snapshots`, `@tmp`, `@swap` with a 96G swapfile), ephemeral tmpfs root, state under
+`@persistent`, `@snapshots`, `@tmp`, `@swap` with a 32G swapfile), ephemeral tmpfs root, state under
 `/persistent` via [preservation.nix](./preservation.nix). Secure Boot via lanzaboote
 ([secureboot.nix](./secureboot.nix)).
 

hosts/idols-aquamarine/disko-fs.nix

@@ -116,10 +116,12 @@
                       "compress-force=zstd:1"
                     ];
                   };
-                  # disko creates the 96G swapfile on this subvolume and adds swapDevices
+                  # disko creates the 32G swapfile on this subvolume and adds swapDevices.
+                  # It is preallocated and never compressed (btrfs swapfile requirements),
+                  # so it consumes its full size on the pool.
                   "@swap" = {
                     mountpoint = "/swap";
-                    swap.swapfile.size = "96G";
+                    swap.swapfile.size = "32G";
                   };
                 };
               };