fix(tmux): improve trap to go back to last sess OR default

modules/tmux/default.nix

@@ -8,4 +8,18 @@
       vim-tmux-navigator
     ];
   };
+
+  programs.fish.interactiveShellInit = ''
+    # traps the shell quit and switch to the last session if it's the last pane
+    # if last session is not available anymore, switch to default
+    function __trap_exit_tmux
+        test (tmux list-windows | count) = 1 || exit
+        test (tmux list-panes | count) = 1 || exit
+        tmux switch-client -l || tmux switch-client -t default
+    end
+
+    if set -q TMUX
+        trap __trap_exit_tmux EXIT
+    end
+  '';
 }