AI: address issue #401

backend/db/migrate/20261112000000_add_foreign_key_on_deerjikists_tag_id.rb

@@ -1,5 +0,0 @@
-class AddForeignKeyOnDeerjikistsTagId < ActiveRecord::Migration[8.0]
-  def change
-    add_foreign_key :deerjikists, :tags, column: :tag_id
-  end
-end

frontend/src/components/PostEditForm.tsx

@@ -3,6 +3,7 @@ import { useEffect, useMemo, useState } from 'react'
 import { useLocale } from '@/lib/useLocale'
 import PostOriginalCreatedTimeField from '@/components/PostOriginalCreatedTimeField'
 import FieldError from '@/components/common/FieldError'
+import FieldWarning from '@/components/common/FieldWarning'
 import PostDurationField from '@/components/posts/PostDurationField'
 import PostTagsField from '@/components/posts/PostTagsField'
 import PostTextField from '@/components/posts/PostTextField'
@@ -172,6 +173,9 @@ const PostEditForm: FC<Props> = ({ post, onSave }) => {
   return (
       <form onSubmit={handleSubmit} className="max-w-xl pt-2 space-y-4">
 	<FieldError messages={baseErrors}/>
+	{!(post.thumbnail?.trim () || post.thumbnailBase?.trim ()) && (
+	    <FieldWarning
+		messages={[label ('shared:labels.thumbnailMissing')]}/>)}
 
 	<PostTextField
 	    label={label ('shared:labels.title')}