ユーザーの古いアカウントを現在のメインアカウントにマージしようとしています。
以前のアカウントが2つありました。1つは比較的小規模（数百件の投稿）、もう1つは1000件以上の投稿がありました。
Webインターフェースから試したところ、時間がかかりましたが、最初のアカウントは完了しました。
2番目のアカウントは「投稿の所有権を変更中」で24時間ハングしており、2回再起動しました。
そのため、代わりに直接rakeコマンドを使用してみたところ、--trace を付けた場合の出力は以下のようになりました。
rake users:merge['user-source','user-target'] --trace
** Invoke users:merge (first_time)
** Invoke environment (first_time)
** Execute environment
** Execute users:merge
rake aborted!
Discourse::InvalidAccess: can_delete_user? failed
/var/www/discourse/lib/guardian/ensure_magic.rb:11:in `method_missing'
/var/www/discourse/app/services/user_destroyer.rb:19:in `destroy'
/var/www/discourse/app/services/user_merger.rb:508:in `delete_source_user'
/var/www/discourse/app/services/user_merger.rb:25:in `merge!'
/var/www/discourse/lib/tasks/users.rake:57:in `block in <main>'
/var/www/discourse/vendor/bundle/ruby/3.2.0/gems/rake-13.0.6/lib/rake/task.rb:279:in `block in execute'
/var/www/discourse/vendor/bundle/ruby/3.2.0/gems/rake-13.0.6/lib/rake/task.rb:279:in `each'
/var/www/discourse/vendor/bundle/ruby/3.2.0/gems/rake-13.0.6/lib/rake/task.rb:279:in `execute'
/var/www/discourse/vendor/bundle/ruby/3.2.0/gems/rake-13.0.6/lib/rake/task.rb:219:in `block in invoke_with_call_chain'
/var/www/discourse/vendor/bundle/ruby/3.2.0/gems/rake-13.0.6/lib/rake/task.rb:199:in `synchronize'
/var/www/discourse/vendor/bundle/ruby/3.2.0/gems/rake-13.0.6/lib/rake/task.rb:199:in `invoke_with_call_chain'
/var/www/discourse/vendor/bundle/ruby/3.2.0/gems/rake-13.0.6/lib/rake/task.rb:188:in `invoke'
/var/www/discourse/vendor/bundle/ruby/3.2.0/gems/rake-13.0.6/lib/rake/application.rb:160:in `invoke_task'
/var/www/discourse/vendor/bundle/ruby/3.2.0/gems/rake-13.0.6/lib/rake/application.rb:116:in `block (2 levels) in top_level'
/var/www/discourse/vendor/bundle/ruby/3.2.0/gems/rake-13.0.6/lib/rake/application.rb:116:in `each'
/var/www/discourse/vendor/bundle/ruby/3.2.0/gems/rake-13.0.6/lib/rake/application.rb:116:in `block in top_level'
/var/www/discourse/vendor/bundle/ruby/3.2.0/gems/rake-13.0.6/lib/rake/application.rb:125:in `run_with_threads'
/var/www/discourse/vendor/bundle/ruby/3.2.0/gems/rake-13.0.6/lib/rake/application.rb:110:in `top_level'
/var/www/discourse/vendor/bundle/ruby/3.2.0/gems/rake-13.0.6/lib/rake/application.rb:83:in `block in run'
/var/www/discourse/vendor/bundle/ruby/3.2.0/gems/rake-13.0.6/lib/rake/application.rb:186:in `standard_exception_handling'
/var/www/discourse/vendor/bundle/ruby/3.2.0/gems/rake-13.0.6/lib/rake/application.rb:80:in `run'
bin/rake:13:in `<top (required)>'
/usr/local/lib/ruby/gems/3.2.0/gems/bundler-2.4.4/lib/bundler/cli/exec.rb:58:in `load'
/usr/local/lib/ruby/gems/3.2.0/gems/bundler-2.4.4/lib/bundler/cli/exec.rb:58:in `kernel_load'
/usr/local/lib/ruby/gems/3.2.0/gems/bundler-2.4.4/lib/bundler/cli/exec.rb:23:in `run'
/usr/local/lib/ruby/gems/3.2.0/gems/bundler-2.4.4/lib/bundler/cli.rb:491:in `exec'
/usr/local/lib/ruby/gems/3.2.0/gems/bundler-2.4.4/lib/bundler/vendor/thor/lib/thor/command.rb:27:in `run'
/usr/local/lib/ruby/gems/3.2.0/gems/bundler-2.4.4/lib/bundler/vendor/thor/lib/thor/invocation.rb:127:in `invoke_command'
/usr/local/lib/ruby/gems/3.2.0/gems/bundler-2.4.4/lib/bundler/vendor/thor/lib/thor.rb:392:in `dispatch'
/usr/local/lib/ruby/gems/3.2.0/gems/bundler-2.4.4/lib/bundler/cli.rb:34:in `dispatch'
/usr/local/lib/ruby/gems/3.2.0/gems/bundler-2.4.4/lib/bundler/vendor/thor/lib/thor/base.rb:485:in `start'
/usr/local/lib/ruby/gems/3.2.0/gems/bundler-2.4.4/lib/bundler/cli.rb:28:in `start'
/usr/local/lib/ruby/gems/3.2.0/gems/bundler-2.4.4/exe/bundle:45:in `block in <top (required)>'
/usr/local/lib/ruby/gems/3.2.0/gems/bundler-2.4.4/lib/bundler/friendly_errors.rb:117:in `with_friendly_errors'
/usr/local/lib/ruby/gems/3.2.0/gems/bundler-2.4.4/exe/bundle:33:in `<top (required)>'
/usr/local/bin/bundle:25:in `load'
/usr/local/bin/bundle:25:in `<main>'
Tasks: TOP => users:merge
ユーザー名は、ユーザーの身元を保護するために置き換えられています。