feat(yami): add dataDir option for storing stack state on separate disk

- Bind-mounts /var/lib/{gitea,postgresql} under configurable dataDir
- gitea-runner intentionally excluded: its DynamicUser + StateDirectory
  conflicts with pre-existing mount points ("File exists")
- Runner token moved to /var/lib/gitea-runner-secret/ to avoid the same
  symlink/StateDirectory conflict inside /var/lib/gitea-runner
- Enable the stack on this host with dataDir = /mnt/ssd_110/yami

configuration.nix

@@ -7,6 +7,7 @@
     ./desktop.nix
     ./nvidia.nix
     ./shell.nix
+    ./yami-dev-stack.nix 
   ];
 
   nix = {
@@ -94,7 +95,14 @@
   programs.gamemode.enable = true;
 
   services.tailscale.enable = true;
-  virtualisation.docker.enable = true;
+  # Docker is now managed by yami-dev-stack.nix when that module is enabled.
+  # services.yami-dev-stack = { enable = true; user = "chexit"; };
+
+  services.yami-dev-stack = {                               
+    enable = true;                                                                                        
+    user   = "chexit";
+    dataDir = "/mnt/ssd_110/yami";
+  };  
 
   system.stateVersion = "25.11";
 }

yami-dev-stack.nix

@@ -0,0 +1,208 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.services.yami-dev-stack;
+in
+{
+  options.services.yami-dev-stack = {
+    enable = mkEnableOption "Yami development stack (gitea, postgres, docker, runner)";
+
+    user = mkOption {
+      type = types.str;
+      description = "User that will own runner token and be added to docker group";
+    };
+
+    dataDir = mkOption {
+      type = types.nullOr types.path;
+      default = null;
+      example = "/mnt/ssd_110/yami";
+      description = ''
+        If set, bind-mounts /var/lib/{gitea,postgresql,gitea-runner} under this
+        path so all stack data lives on a separate disk. Directories are created
+        automatically; existing data must be rsync'd manually before enabling.
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable (mkMerge [ {
+
+    # ── Systemd target ─────────────────────────────────────────────────────────
+    # Manual-only: nothing in wantedBy, so it never starts on boot.
+    systemd.targets.yami-dev = {
+      description = "Yami development stack (gitea, postgres, docker, runner)";
+      wantedBy = [ ];
+    };
+
+    # ── PostgreSQL 16 ──────────────────────────────────────────────────────────
+    services.postgresql = {
+      enable = true;
+      package = pkgs.postgresql_16;
+      ensureDatabases = [ "gitea" ];
+      ensureUsers = [
+        {
+          name = "gitea";
+          ensureDBOwnership = true;
+        }
+      ];
+    };
+
+    # Pull postgres under yami-dev.target; stop it when target stops.
+    systemd.services.postgresql = {
+      wantedBy = mkForce [ "yami-dev.target" ];
+      partOf   = [ "yami-dev.target" ];
+    };
+
+    # ── Gitea ──────────────────────────────────────────────────────────────────
+    services.gitea = {
+      enable   = true;
+      appName  = "Yami Git";
+
+      # LFS enabled via the NixOS helper so the module manages LFS_JWT_SECRET
+      # (writing it to app.ini, which is read-only by design).
+      lfs.enable = true;
+
+      database = {
+        type   = "postgres";
+        socket = "/run/postgresql";
+        name   = "gitea";
+        user   = "gitea";
+      };
+
+      settings = {
+        server = {
+          DOMAIN           = "localhost";
+          ROOT_URL         = "http://localhost:3000/";
+          HTTP_ADDR        = "0.0.0.0";
+          HTTP_PORT        = 3000;
+          SSH_PORT         = 2222;
+          START_SSH_SERVER = true;
+        };
+
+        service = {
+          DISABLE_REGISTRATION      = true;
+          DEFAULT_KEEP_EMAIL_PRIVATE = true;
+        };
+
+        repository = {
+          DEFAULT_BRANCH         = "main";
+          ENABLE_PUSH_CREATE_USER = true;
+          ENABLE_PUSH_CREATE_ORG  = true;
+        };
+
+        actions = {
+          ENABLED             = true;
+          DEFAULT_ACTIONS_URL = "github";
+          LOG_RETENTION_DAYS  = 14;
+          ARTIFACT_RETENTION_DAYS = 30;
+        };
+
+        packages = {
+          ENABLED = true;
+        };
+
+        session = {
+          COOKIE_SECURE = false;
+        };
+
+        "cron.git_gc_repos" = {
+          ENABLED  = true;
+          SCHEDULE = "@every 72h";
+          ARGS     = "--aggressive --prune=now";
+        };
+      };
+    };
+
+    systemd.services.gitea = {
+      wantedBy = mkForce [ "yami-dev.target" ];
+      partOf   = [ "yami-dev.target" ];
+      after    = [ "postgresql.service" ];
+      requires = [ "postgresql.service" ];
+    };
+
+    # ── Docker ─────────────────────────────────────────────────────────────────
+    virtualisation.docker = {
+      enable      = true;
+      enableOnBoot = false;
+    };
+
+    systemd.services.docker = {
+      wantedBy = mkForce [ "yami-dev.target" ];
+      partOf   = [ "yami-dev.target" ];
+    };
+
+    users.users.${cfg.user}.extraGroups = [ "docker" ];
+
+    # ── Gitea Actions Runner ───────────────────────────────────────────────────
+    services.gitea-actions-runner.instances.default = {
+      enable    = true;
+      name      = "home-runner";
+      url       = "http://localhost:3000";
+      # NOT under /var/lib/gitea-runner — that path is systemd-managed for the
+      # service (DynamicUser + StateDirectory means it becomes a symlink to
+      # /var/lib/private/gitea-runner). Pre-creating it ourselves breaks the
+      # service with "Failed to set up special execution directory: File exists".
+      tokenFile = "/var/lib/gitea-runner-secret/token";
+      labels    = [
+        "ubuntu-latest:docker://node:20"
+        "native:host"
+      ];
+    };
+
+    systemd.services."gitea-runner-default" = {
+      wantedBy = mkForce [ "yami-dev.target" ];
+      partOf   = [ "yami-dev.target" ];
+      after    = [ "gitea.service" "docker.service" ];
+      requires = [ "gitea.service" "docker.service" ];
+    };
+
+    # Runner uses DynamicUser, so there's no static gitea-runner user/group.
+    # Token lives in a sibling dir (not /var/lib/gitea-runner — that's systemd's
+    # StateDirectory and pre-creating it breaks DynamicUser bind setup).
+    # The file MUST be in env-file format, not a raw token:
+    #     TOKEN=<paste-registration-token-from-gitea-ui>
+    # Get the token from Site Administration → Actions → Runners → Create new Runner.
+    systemd.tmpfiles.rules = [
+      "d /var/lib/gitea-runner-secret 0700 root root -"
+    ];
+
+    # ── Shell aliases ──────────────────────────────────────────────────────────
+    environment.shellAliases = {
+      yami-up     = "sudo systemctl start yami-dev.target && echo 'Gitea → http://localhost:3000'";
+      yami-down   = "sudo systemctl stop yami-dev.target && echo 'Yami dev stack stopped'";
+      yami-status = "systemctl status yami-dev.target gitea postgresql docker gitea-runner-default --no-pager";
+      yami-logs   = "journalctl -u gitea -u gitea-runner-default -f";
+    };
+
+    # ── Firewall ───────────────────────────────────────────────────────────────
+    # Merged with existing rules (Steam etc.); does not overwrite them.
+    networking.firewall.allowedTCPPorts = [ 3000 2222 ];
+  }
+
+  # ── Optional: move all stack data to a separate disk via bind-mounts ─────────
+  (mkIf (cfg.dataDir != null) (
+    let
+      # gitea-runner intentionally NOT bind-mounted: its service uses
+      # DynamicUser + StateDirectory, which refuses to adopt an existing
+      # mount point ("Failed to set up special execution directory: File exists").
+      # Its data is tiny (token + .runner state) so it stays on the system disk.
+      subs = [ "gitea" "postgresql" ];
+      mkBind = name: {
+        name = "/var/lib/${name}";
+        value = {
+          device  = "${cfg.dataDir}/${name}";
+          fsType  = "none";
+          options = [ "bind" ];
+        };
+      };
+    in {
+      # Ensure target dirs exist on the data disk before mounts happen.
+      systemd.tmpfiles.rules = map (n: "d ${cfg.dataDir}/${n} 0755 root root -") subs
+        ++ [ "d ${cfg.dataDir} 0755 root root -" ];
+
+      fileSystems = listToAttrs (map mkBind subs);
+    }
+  ))
+  ]);
+}