#399

backend/app/controllers/posts_controller.rb

@@ -216,7 +216,8 @@ class PostsController < ApplicationController
 
     preflight = PostCreatePreflight.new(
         attributes: post_create_attributes,
-        thumbnail: params[:thumbnail]).run
+        thumbnail: params[:thumbnail],
+        host: request.base_url).run
     return render json: dry_run_json(preflight) if bool?(:dry)
     if preflight[:existing_post_id].present?
       post = Post.new(url: preflight[:url])
@@ -273,7 +274,11 @@ class PostsController < ApplicationController
     return head :payload_too_large if request.content_length.to_i > MAX_BULK_REQUEST_BYTES
     posts = parse_bulk_posts_manifest
     thumbnails = parse_bulk_thumbnails(posts.length)
-    result = PostBulkCreator.new(actor: current_user, posts:, thumbnails:).run
+    result = PostBulkCreator.new(
+        actor: current_user,
+        posts:,
+        thumbnails:,
+        host: request.base_url).run
     render json: result
   rescue JSON::ParserError
     render_bad_request 'posts manifest の JSON が不正です．'
@@ -627,7 +632,7 @@ class PostsController < ApplicationController
     return nil if post_id.blank?
 
     post = Post.with_attached_thumbnail.find_by(id: post_id)
-    PostCompactRepr.base(post)
+    PostCompactRepr.base(post, host: request.base_url)
   end
 
   def dry_run_json preflight