feat: Add unified Call model for voice calling (#14026)

Adds a Call model to track voice call state across providers (Twilio,
WhatsApp). This replaces storing call data in
conversation.additional_attributes and provides a foundation for call
analytics multi-call-per-conversation support, and future voice
providers.

---------

Co-authored-by: Muhsin <12408980+muhsin-k@users.noreply.github.com>

enterprise/app/models/call.rb

@@ -0,0 +1,55 @@
+# == Schema Information
+#
+# Table name: calls
+#
+#  id                   :bigint           not null, primary key
+#  direction            :integer          not null
+#  duration_seconds     :integer
+#  end_reason           :string
+#  meta                 :jsonb
+#  provider             :integer          default("twilio"), not null
+#  started_at           :datetime
+#  status               :string           default("ringing"), not null
+#  transcript           :text
+#  created_at           :datetime         not null
+#  updated_at           :datetime         not null
+#  accepted_by_agent_id :bigint
+#  account_id           :bigint           not null
+#  contact_id           :bigint           not null
+#  conversation_id      :bigint           not null
+#  inbox_id             :bigint           not null
+#  message_id           :bigint
+#  provider_call_id     :string           not null
+#
+# Indexes
+#
+#  index_calls_on_account_id_and_contact_id       (account_id,contact_id)
+#  index_calls_on_account_id_and_conversation_id  (account_id,conversation_id)
+#  index_calls_on_message_id                      (message_id)
+#  index_calls_on_provider_and_provider_call_id   (provider,provider_call_id) UNIQUE
+#
+class Call < ApplicationRecord
+  # All valid call statuses
+  STATUSES = %w[ringing in_progress completed no_answer failed].freeze
+  # Statuses where the call is finished and won't change again
+  TERMINAL_STATUSES = %w[completed no_answer failed].freeze
+
+  enum :provider, { twilio: 0, whatsapp: 1 }
+  enum :direction, { incoming: 0, outgoing: 1 }
+
+  belongs_to :account
+  belongs_to :inbox
+  belongs_to :conversation
+  belongs_to :contact
+  belongs_to :message, optional: true
+  belongs_to :accepted_by_agent, class_name: 'User', optional: true
+
+  has_one_attached :recording
+
+  validates :provider_call_id, presence: true
+  validates :provider, presence: true
+  validates :direction, presence: true
+  validates :status, presence: true, inclusion: { in: STATUSES }
+
+  scope :active, -> { where.not(status: TERMINAL_STATUSES) }
+end

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

@@ -17,6 +17,7 @@ module Enterprise::Concerns::Account
     has_many :copilot_threads, dependent: :destroy_async
     has_many :companies, dependent: :destroy_async
     has_many :voice_channels, dependent: :destroy_async, class_name: '::Channel::Voice'
+    has_many :calls, dependent: :destroy_async
 
     has_one :saml_settings, dependent: :destroy_async, class_name: 'AccountSamlSettings'
   end

enterprise/app/models/enterprise/concerns/conversation.rb

@@ -5,6 +5,7 @@ module Enterprise::Concerns::Conversation
     belongs_to :sla_policy, optional: true
     has_one :applied_sla, dependent: :destroy_async
     has_many :sla_events, dependent: :destroy_async
+    has_many :calls, dependent: :destroy_async
     has_many :captain_responses, class_name: 'Captain::AssistantResponse', dependent: :nullify, as: :documentable
     before_validation :validate_sla_policy, if: -> { sla_policy_id_changed? }
     around_save :ensure_applied_sla_is_created, if: -> { sla_policy_id_changed? }

enterprise/app/models/enterprise/concerns/inbox.rb

@@ -7,5 +7,6 @@ module Enterprise::Concerns::Inbox
             through: :captain_inbox,
             class_name: 'Captain::Assistant'
     has_many :inbox_capacity_limits, dependent: :destroy
+    has_many :calls, dependent: :destroy_async
   end
 end

enterprise/app/models/enterprise/concerns/message.rb

@@ -0,0 +1,7 @@
+module Enterprise::Concerns::Message
+  extend ActiveSupport::Concern
+
+  included do
+    has_one :call, dependent: :nullify
+  end
+end