I accidentally deleted the Markdown filter module from the file system while it was still enabled. So I installed it again, via the GUI.
Now I cannot load the module uninstall page - it says "The website encountered an unexpected error. Please try again later", and the message in the log says
Drupal\Component\Plugin\Exception\PluginNotFoundException: The "markdown" plugin does not exist. in Drupal\Core\Plugin\DefaultPluginManager->doGetDefinition()
I have cleared caches, run cron, deleted
sites/default/files/php ... all to no avail.
Edit: I have just tried to enable the module again, and got this message:
Unable to install Markdown filter, markdown.settings already exists in active configuration. I looked through the config and cache_config tables and cannot find this setting.