workaround to strange onMount bug with many Tabs components

packages/builder/src/pages/builder/portal/manage/email/[template].svelte

@@ -1,4 +1,5 @@
 <script>
+  import { onMount } from "svelte"
   import {
     Button,
     Detail,
@@ -19,6 +20,7 @@
   export let template
 
   let htmlEditor
+  let mounted = false
 
   $: selectedTemplate = $email?.templates?.find(
     ({ purpose }) => purpose === template
@@ -39,6 +41,9 @@
   function setTemplateBinding(binding) {
     htmlEditor.update((selectedTemplate.contents += `{{ ${binding.name} }}`))
   }
+  onMount(() => {
+    mounted = true
+  })
 </script>
 
 <Page wide>
@@ -78,6 +83,7 @@
         />
         <div class="bindings-editor">
           <Detail size="L">Bindings</Detail>
+          {#if mounted}
             <Tabs selected="Template">
               <Tab title="Template">
                 <TemplateBindings
@@ -94,6 +100,7 @@
                 />
               </Tab>
             </Tabs>
+          {/if}
         </div>
       </div></Tab
     >
@@ -108,7 +115,7 @@
 <style>
   .template-editor {
     display: grid;
-    grid-template-columns: 1fr 20%;
+    grid-template-columns: 1fr minmax(250px, 20%);
     grid-gap: var(--spacing-xl);
     margin-top: var(--spacing-xl);
   }