fix: Update specs, add background response job implementation for copilot threads (#11600)

- Enable jobs by default when a copilot thread or a message is created.
- Rename thread_id to copilot_thread_id to keep it consistent with the
model name
- Add a spec for search_linear_issues service

enterprise/app/models/copilot_message.rb

@@ -19,14 +19,12 @@ class CopilotMessage < ApplicationRecord
   belongs_to :copilot_thread
   belongs_to :account
 
-  before_validation :ensure_account
-
   enum message_type: { user: 0, assistant: 1, assistant_thinking: 2 }
 
-  validates :message_type, presence: true, inclusion: { in: message_types.keys }
+  validates :message_type, presence: true
   validates :message, presence: true
+  before_validation :ensure_account
   validate :validate_message_attributes
-
   after_create_commit :broadcast_message
 
   def push_event_data
@@ -39,10 +37,20 @@ class CopilotMessage < ApplicationRecord
     }
   end
 
+  def enqueue_response_job(conversation_id, user_id)
+    Captain::Copilot::ResponseJob.perform_later(
+      assistant: copilot_thread.assistant,
+      conversation_id: conversation_id,
+      user_id: user_id,
+      copilot_thread_id: copilot_thread.id,
+      message: message['content']
+    )
+  end
+
   private
 
   def ensure_account
-    self.account = copilot_thread.account
+    self.account_id = copilot_thread&.account_id
   end
 
   def broadcast_message