Archive webmentions if they have been removed from their source

db/migrate/20240210232136_add_last_checked_at_to_webmentions.rb

@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+ROM::SQL.migration do
+  change do
+    alter_table :webmentions do
+      add_column :last_checked_at, :timestamp
+    end
+  end
+end