feat: Add support for persistent copilot threads and messages (#11489)

The agents can see the previous conversations with the copilot if needed
with this change. We would have to cleanup the data after a while. For
now, that is not considered.

This PR adds:
- A new model for copilot_threads (intentionally named thread instead of
conversation to avoid confusion), copilot_messages
- Add the controller to fetch previous threads and messages.

enterprise/app/models/copilot_message.rb

@@ -0,0 +1,27 @@
+# == Schema Information
+#
+# Table name: copilot_messages
+#
+#  id                :bigint           not null, primary key
+#  message           :jsonb            not null
+#  message_type      :string           not null
+#  created_at        :datetime         not null
+#  updated_at        :datetime         not null
+#  account_id        :bigint           not null
+#  copilot_thread_id :bigint           not null
+#  user_id           :bigint           not null
+#
+# Indexes
+#
+#  index_copilot_messages_on_account_id         (account_id)
+#  index_copilot_messages_on_copilot_thread_id  (copilot_thread_id)
+#  index_copilot_messages_on_user_id            (user_id)
+#
+class CopilotMessage < ApplicationRecord
+  belongs_to :copilot_thread
+  belongs_to :user
+  belongs_to :account
+
+  validates :message_type, presence: true, inclusion: { in: %w[user assistant assistant_thinking] }
+  validates :message, presence: true
+end

enterprise/app/models/copilot_thread.rb

@@ -0,0 +1,26 @@
+# == Schema Information
+#
+# Table name: copilot_threads
+#
+#  id         :bigint           not null, primary key
+#  title      :string           not null
+#  uuid       :uuid             not null
+#  created_at :datetime         not null
+#  updated_at :datetime         not null
+#  account_id :bigint           not null
+#  user_id    :bigint           not null
+#
+# Indexes
+#
+#  index_copilot_threads_on_account_id  (account_id)
+#  index_copilot_threads_on_user_id     (user_id)
+#  index_copilot_threads_on_uuid        (uuid) UNIQUE
+#
+class CopilotThread < ApplicationRecord
+  belongs_to :user
+  belongs_to :account
+  has_many :copilot_messages, dependent: :destroy
+
+  validates :title, presence: true
+  validates :uuid, presence: true, uniqueness: true
+end

enterprise/app/models/enterprise/concerns/account.rb

@@ -9,5 +9,7 @@ module Enterprise::Concerns::Account
     has_many :captain_assistants, dependent: :destroy_async, class_name: 'Captain::Assistant'
     has_many :captain_assistant_responses, dependent: :destroy_async, class_name: 'Captain::AssistantResponse'
     has_many :captain_documents, dependent: :destroy_async, class_name: 'Captain::Document'
+
+    has_many :copilot_threads, dependent: :destroy_async
   end
 end

enterprise/app/models/enterprise/concerns/user.rb

@@ -5,6 +5,8 @@ module Enterprise::Concerns::User
     before_validation :ensure_installation_pricing_plan_quantity, on: :create
 
     has_many :captain_responses, class_name: 'Captain::AssistantResponse', dependent: :nullify, as: :documentable
+    has_many :copilot_threads, dependent: :destroy_async
+    has_many :copilot_messages, dependent: :destroy_async
   end
 
   def ensure_installation_pricing_plan_quantity