fix(voice): guarantee conference_sid at TwiML render, consistent Call factory

- conference_twiml now ensures call.conference_sid is present before
  rendering; backfills via Voice::Conference::Name.for(call) if missing.
  Prevents invalid TwiML on Call rows created without the sid set.
- Call factory derives account/inbox/contact from the associated
  conversation so create(:call) is always internally consistent (no more
  mismatched account_id across associations).

enterprise/app/controllers/twilio/voice_controller.rb

@@ -114,10 +114,12 @@ class Twilio::VoiceController < ApplicationController
   end
 
   def conference_twiml(call)
+    conference_sid = ensure_conference_sid!(call)
+
     Twilio::TwiML::VoiceResponse.new.tap do |response|
       response.dial do |dial|
         dial.conference(
-          call.conference_sid,
+          conference_sid,
           start_conference_on_enter: agent_leg?(twilio_from),
           end_conference_on_exit: false,
           status_callback: conference_status_callback_url,
@@ -129,6 +131,13 @@ class Twilio::VoiceController < ApplicationController
     end.to_s
   end
 
+  def ensure_conference_sid!(call)
+    return call.conference_sid if call.conference_sid.present?
+
+    call.update!(conference_sid: Voice::Conference::Name.for(call))
+    call.conference_sid
+  end
+
   def participant_label_for(from_number)
     return from_number.delete_prefix('client:') if from_number.start_with?('client:')
 

spec/factories/calls.rb

@@ -1,9 +1,9 @@
 FactoryBot.define do
   factory :call do
-    association :account
-    association :inbox
     association :conversation
-    association :contact
+    account { conversation.account }
+    inbox { conversation.inbox }
+    contact { conversation.contact }
     provider { :twilio }
     direction { :incoming }
     status { 'ringing' }