fix(call): emit assignee activity message when agent answers a call (#14700)

## Linear Ticket
- https://linear.app/chatwoot/issue/CW-7249/debug-assignment-log

## Description

When an agent answers an inbound WhatsApp call on an unassigned
conversation, the conversation is claimed for that agent — but no
"assigned" activity message or assignee-changed event was emitted, so
the assignment was invisible in the timeline (and notifications/live
assignee panel didn't update).

The claim ran before `update_conversation_call_status`, so that later
`update!` on the same conversation clobbered
`saved_change_to_assignee_id?` before `after_commit` fired. Moving the
claim to be the conversation's final write in the transaction restores
the activity message, the `ASSIGNEE_CHANGED` event, and the live
assignee update.

## Type of change

- [ ] Bug fix (non-breaking change which fixes an issue)

## How Has This Been Tested?

1. Open an unassigned WhatsApp-call conversation.
2. As an agent, answer an inbound call.
3. Before: the conversation is assigned to you, but no "self-assigned"
activity message appears. After: the activity message is created and the
assignee updates live.

## Checklist:

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

enterprise/app/services/whatsapp/call_service.rb

@@ -9,7 +9,7 @@ class Whatsapp::CallService
     call.with_lock do
       transition_to_in_progress!
       update_message_status('in_progress')
-      update_conversation_call_status(call.display_status)
+      claim_conversation_and_set_call_status
       broadcast(:accepted, accepted_by_agent_id: agent.id)
     end
     call
@@ -56,7 +56,6 @@ class Whatsapp::CallService
     forward_answer_to_meta!
     call.update!(status: 'in_progress', accepted_by_agent_id: agent.id, started_at: Time.current,
                  meta: (call.meta || {}).merge('sdp_answer' => sdp_answer))
-    claim_conversation_for_agent
   end
 
   def forward_answer_to_meta!
@@ -64,9 +63,13 @@ class Whatsapp::CallService
     invoke_provider!(:accept_call, sdp_answer)
   end
 
-  # Take ownership of the conversation if no one holds it; leave assignee alone otherwise (transfer via UI).
-  def claim_conversation_for_agent
-    call.conversation.update!(assignee: agent) if call.conversation.assignee_id.blank?
+  # Claim an unheld conversation and set call_status in one save so previous_changes carries both the
+  # assignee change (activity message + ASSIGNEE_CHANGED) and the call_status change (conversation.updated webhook).
+  def claim_conversation_and_set_call_status
+    conversation = call.conversation
+    attrs = { additional_attributes: (conversation.additional_attributes || {}).merge('call_status' => call.display_status) }
+    attrs[:assignee] = agent if conversation.assignee_id.blank?
+    conversation.update!(attrs)
   end
 
   # Raise on Meta failure (bool false or transport error) so callers bail before