Fix account migration not affecting followers on origin server (#11980)

app/workers/move_worker.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+class MoveWorker
+  include Sidekiq::Worker
+
+  def perform(source_account_id, target_account_id)
+    @source_account = Account.find(source_account_id)
+    @target_account = Account.find(target_account_id)
+
+    if @target_account.local?
+      rewrite_follows!
+    else
+      queue_follow_unfollows!
+    end
+  rescue ActiveRecord::RecordNotFound
+    true
+  end
+
+  private
+
+  def rewrite_follows!
+    @source_account.passive_relationships
+                   .where(account: Account.local)
+                   .in_batches
+                   .update_all(target_account: @target_account)
+  end
+
+  def queue_follow_unfollows!
+    @source_account.followers.local.select(:id).find_in_batches do |accounts|
+      UnfollowFollowWorker.push_bulk(accounts.map(&:id)) { |follower_id| [follower_id, @source_account.id, @target_account.id] }
+    end
+  end
+end