feat(sirius): enable impermanence

modules/hosts/sirius/config.nix

@@ -18,6 +18,7 @@
 
       tnix = {
         boot.secure-boot.enable = true;
+        boot.impermanence.enable = true;
         networking.openssh.enable = true;
 
         virtualisation = {

modules/hosts/sirius/disko.nix

@@ -0,0 +1,82 @@
+{ inputs, ... }:
+{
+  flake.modules.nixos.sirius =
+    { config, lib, ... }:
+    let
+      hasOptinPersistence = config.tnix.boot.impermanence.enable;
+    in
+    {
+      imports = [
+        inputs.disko.nixosModules.disko
+      ];
+
+      disko.devices.disk.primary = {
+        device = "/dev/nvme1n1";
+        type = "disk";
+        content = {
+          type = "gpt";
+          partitions = {
+            ESP = {
+              size = "1G";
+              type = "EF00";
+              content = {
+                type = "filesystem";
+                format = "vfat";
+                mountpoint = "/boot";
+                mountOptions = [
+                  "defaults"
+                  "umask=0077"
+                ];
+              };
+            };
+            swap = {
+              size = "70G";
+              content = {
+                type = "swap";
+                discardPolicy = "both";
+                resumeDevice = true;
+              };
+            };
+            root = {
+              size = "100%";
+              type = "8300";
+              content = {
+                type = "btrfs";
+                # Base subvolumes that always exist
+                subvolumes = {
+                  "/root" = {
+                    mountOptions = [
+                      "compress=zstd"
+                      "noatime"
+                      "space_cache=v2"
+                    ];
+                    mountpoint = "/";
+                  };
+                  "/nix" = {
+                    mountOptions = [
+                      "compress=zstd"
+                      "noatime"
+                      "noacl"
+                      "space_cache=v2"
+                    ];
+                    mountpoint = "/nix";
+                  };
+                }
+                # Conditionally merge /persist only when impermanence is enabled
+                // lib.optionalAttrs hasOptinPersistence {
+                  "/persist" = {
+                    mountOptions = [
+                      "compress=zstd"
+                      "noatime"
+                      "space_cache=v2"
+                    ];
+                    mountpoint = "/persist";
+                  };
+                };
+              };
+            };
+          };
+        };
+      };
+    };
+}