i3: use a saved layout to spawn Emacs workspace

This works great!

config

@@ -160,7 +160,7 @@ for_window [window_role="PictureInPicture"] floating enable
 # Start stuff
 exec_always --no-startup-id systemctl --user start --no-block i3-session.target
 exec --no-startup-id i3-msg "\
-  workspace number 1; exec emacs; exec $term; exec $term; \
+  workspace number 1; append_layout ~/.config/i3/ws-emacs.json; exec emacs; exec $term; exec $term; \
   workspace number 2; layout tabbed; exec firefox; \
   workspace number 3; exec spotify; \
   workspace number 1"

ws-emacs.json

@@ -0,0 +1,15 @@
+{
+    "layout": "splith",
+    "percent": 1,
+    "nodes": [
+        {"swallows": [{"class": "^Emacs$"}], "percent": 0.62},
+        {
+            "layout": "splitv",
+            "percent": 0.38,
+            "nodes": [
+                {"swallows": [{"class": "^Vbeterm$"}]},
+                {"swallows": [{"class": "^Vbeterm$"}]}
+            ]
+        }
+    ]
+}