--- a/backend/lib/tasks/sync_nico.rake
+++ b/backend/lib/tasks/sync_nico.rake
@@ -47,11 +47,18 @@ namespace :nico do
      code = datum['code']
      post = Post.where('url REGEXP ?', "nicovideo\\.jp/watch/#{ Regexp.escape(code) }([^0-9]|$)")
                 .first
      unless post
        title = datum['title']
      title = datum['title']
      original_created_at = datum['uploaded_at'] && Time.iso8601(datum['uploaded_at'])
      original_created_from = original_created_at&.change(sec: 0)
      original_created_before = original_created_from&.+(1.minute)
      if post
        attrs = { title:, original_created_from:, original_created_before: }
        post.update!(attrs) if attrs.any? { |k, v| post.public_send(k) != v }
      else
        url = "https://www.nicovideo.jp/watch/#{ code }"
        thumbnail_base = fetch_thumbnail.(url) rescue nil
        post = Post.new(title:, url:, thumbnail_base:, uploaded_user: nil)
        post = Post.new(title:, url:, thumbnail_base:, uploaded_user: nil,
                        original_created_from:, original_created_before:)
        if thumbnail_base.present?
          post.thumbnail.attach(
              io:           URI.open(thumbnail_base),
--- a/backend/spec/tasks/nico_sync_spec.rb
+++ b/backend/spec/tasks/nico_sync_spec.rb
@@ -13,7 +13,6 @@ RSpec.describe "nico:sync" do
  end

  def link_nico_to_tag!(nico_tag, tag)
    # NicoTagRelation がある前提（君の model からそう見える）
    NicoTagRelation.create!(nico_tag_id: nico_tag.id, tag_id: tag.id)
  end

@@ -35,7 +34,12 @@ RSpec.describe "nico:sync" do
    Tag.tagme

    # pythonの出力（AAA が付く）
    stub_python([{ "code" => "sm9", "title" => "t", "tags" => ["AAA"] }])
    stub_python([{
        'code' => 'sm9',
        'title' => 't',
        'tags' => ['AAA'],
        'uploaded_at' => '2026-01-01T12:34:56+09:00',
        'deleted_at' => '2026-01-31T00:00:00+09:00' }])

    # 外部HTTPは今回「既存 post なので呼ばれない」はずだが、念のため塞ぐ
    allow(URI).to receive(:open).and_return(StringIO.new("<html></html>"))
@@ -49,6 +53,9 @@ RSpec.describe "nico:sync" do
    expect(active_tag_names).to include("nico:AAA")
    expect(active_tag_names).to include("spec_linked")

    expect(post.original_created_from).to eq(Time.iso8601('2026-01-01T03:34:00Z'))
    expect(post.original_created_before).to eq(Time.iso8601('2026-01-01T03:35:00Z'))

    # 差分が出るので bot が付く（kept_non_nico_ids != desired_non_nico_ids）
    expect(active_tag_names).to include("bot操作")
  end