smug: add project session setting

Add an optional session setting so that session names can be different
than the smug project name. This also enables using template variables
when naming sessions.

modules/misc/news/2026/03/2026-03-15_13-42-27.nix

@@ -0,0 +1,9 @@
+{ config, pkgs, ... }:
+{
+  time = "2026-03-15T20:42:27+00:00";
+  condition = true;
+  message = ''
+    programs.smug.projects.<name>.session is a new optional setting that
+    can be used to specify a different session name from the project name.
+  '';
+}

modules/programs/smug.nix

@@ -37,9 +37,17 @@ in
 
     projects = lib.mkOption {
       type = lib.types.attrsOf (
-        lib.types.submodule [
+        lib.types.submodule (
+          { name, ... }:
           {
             options = {
+              session = lib.mkOption {
+                type = lib.types.str;
+                default = name;
+                description = "Session name for the smug project.";
+                example = lib.literalExpression ''{ session = "project-\''${worktree}"; }'';
+              };
+
               root = mkOptionRoot ''
                 Root path in filesystem of the smug project. This is where tmux
                 changes its directory to.
@@ -139,7 +147,7 @@ in
               stop = mkOptionCommands "Commands to execute after the tmux-session is destroyed.";
             };
           }
-        ]
+        )
       );
       default = { };
       description = "Attribute set with project configurations.";
@@ -161,7 +169,7 @@ in
                   (lib.attrsets.nameValuePair (if name == "beforeStart" then "before_start" else name) value)
                 ) v
                 // {
-                  session = k;
+                  session = v.session;
                   windows = lib.lists.forEach v.windows (
                     winprop: (lib.filterAttrsRecursive (name: value: value != null) winprop)
                   );

tests/modules/programs/smug/project.yml

@@ -0,0 +1,5 @@
+root: ~/project
+session: project-${worktree}
+windows:
+- layout: tiled
+  name: src

tests/modules/programs/smug/settings.nix

@@ -53,11 +53,23 @@
           ];
         };
 
+        project = {
+          root = "~/project";
+          session = "project-\${worktree}";
+          windows = [
+            {
+              name = "src";
+              layout = "tiled";
+            }
+          ];
+        };
+
       };
     };
   };
 
   nmt.script = ''
     assertFileContent home-files/.config/smug/blogdemo.yml ${./blogdemo.yml}
+    assertFileContent home-files/.config/smug/project.yml ${./project.yml}
   '';
 }