FEATURE: Allow plugins to register a callback to ignore DraftSequence.

app/models/draft_sequence.rb

@@ -5,7 +5,7 @@ class DraftSequence < ActiveRecord::Base
     user_id = user
     user_id = user.id unless user.is_a?(Integer)
 
-    return 0 if user_id < 0
+    return 0 if invalid_user_id?(user_id)
 
     h = { user_id: user_id, draft_key: key }
     c = DraftSequence.find_by(h)
@@ -23,12 +23,22 @@ class DraftSequence < ActiveRecord::Base
     user_id = user
     user_id = user.id unless user.is_a?(Integer)
 
-    return nil if user_id < 0
+    return nil if invalid_user_id?(user_id)
 
     # perf critical path
     r, _ = DB.query_single('select sequence from draft_sequences where user_id = ? and draft_key = ?', user_id, key)
     r.to_i
   end
+
+  cattr_accessor :plugin_ignore_draft_sequence_callbacks
+  self.plugin_ignore_draft_sequence_callbacks = {}
+
+  def self.invalid_user_id?(user_id)
+    user_id < 0 || self.plugin_ignore_draft_sequence_callbacks.any? do |plugin, callback|
+      plugin.enabled? ? callback.call(user_id) : false
+    end
+  end
+  private_class_method :invalid_user_id?
 end
 
 # == Schema Information