fix: Enforce team boundaries to prevent cross-team assignments (#13353)

## Description

Fixes a critical bug where conversations assigned to a team could be
auto-assigned to agents outside that team when all team members were at
capacity.

## Type of change

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

## 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

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Medium Risk**
> Changes core assignment selection for both legacy and v2 flows;
misconfiguration of `allow_auto_assign` or team membership could cause
conversations to remain unassigned.
> 
> **Overview**
> Prevents auto-assignment from crossing team boundaries by filtering
eligible agents to the conversation’s `team` members (and requiring
`team.allow_auto_assign`) in both the legacy `AutoAssignmentHandler`
path and the v2 `AutoAssignment::AssignmentService` (including the
Enterprise override).
> 
> Adds test coverage to ensure team-scoped conversations only assign to
team members, and are skipped when team auto-assign is disabled or no
team members are available; also updates the conversations controller
spec setup to include team membership.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
67ed2bda0cd8ffd56c7e0253b86369dead2e6155. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

app/models/concerns/auto_assignment_handler.rb

@@ -19,10 +19,18 @@ module AutoAssignmentHandler
       AutoAssignment::AssignmentJob.perform_later(inbox_id: inbox.id)
     else
       # Use legacy assignment system
-      AutoAssignment::AgentAssignmentService.new(conversation: self, allowed_agent_ids: inbox.member_ids_with_assignment_capacity).perform
+      # If conversation has a team, only consider team members for assignment
+      allowed_agent_ids = team_id.present? ? team_member_ids_with_capacity : inbox.member_ids_with_assignment_capacity
+      AutoAssignment::AgentAssignmentService.new(conversation: self, allowed_agent_ids: allowed_agent_ids).perform
     end
   end
 
+  def team_member_ids_with_capacity
+    return [] if team.blank? || team.allow_auto_assign.blank?
+
+    inbox.member_ids_with_assignment_capacity & team.members.ids
+  end
+
   def should_run_auto_assignment?
     return false unless inbox.enable_auto_assignment?
 

app/services/auto_assignment/assignment_service.rb

@@ -19,7 +19,7 @@ class AutoAssignment::AssignmentService
   def perform_for_conversation(conversation)
     return false unless assignable?(conversation)
 
-    agent = find_available_agent
+    agent = find_available_agent(conversation)
     return false unless agent
 
     assign_conversation(conversation, agent)
@@ -44,13 +44,26 @@ class AutoAssignment::AssignmentService
     scope.limit(limit)
   end
 
-  def find_available_agent
-    agents = filter_agents_by_rate_limit(inbox.available_agents)
+  def find_available_agent(conversation = nil)
+    agents = filter_agents_by_team(inbox.available_agents, conversation)
+    return nil if agents.nil?
+
+    agents = filter_agents_by_rate_limit(agents)
     return nil if agents.empty?
 
     round_robin_selector.select_agent(agents)
   end
 
+  def filter_agents_by_team(agents, conversation)
+    return agents if conversation&.team_id.blank?
+
+    team = conversation.team
+    return nil if team.blank? || team.allow_auto_assign.blank?
+
+    team_member_ids = team.members.ids
+    agents.where(user_id: team_member_ids)
+  end
+
   def filter_agents_by_rate_limit(agents)
     agents.select do |agent_member|
       rate_limiter = build_rate_limiter(agent_member.user)