fix: resolve V2 capacity bypass in team assignment (#13904)

## Description

When Assignment V2 is enabled, the V2 capacity policies
(AgentCapacityPolicy / InboxCapacityLimit) are not respected during
team-based assignment paths. The system falls back to the legacy V1
max_assignment_limit, and since V1 is deprecated and typically
unconfigured in V2 setups, agents receive unlimited assignments
regardless of their V2 capacity.

Root cause: Inbox class directly defined
member_ids_with_assignment_capacity, which shadowed the
Enterprise::InboxAgentAvailability module override in Ruby's method
resolution order (MRO). This made the V2 capacity check unreachable
(dead code) for any code path using member_ids_with_assignment_capacity.

## Type of change

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

## How Has This Been Tested?

⏺ Before the fix
1. Enable assignment_v2 + advanced_assignment on account
2. Create AgentCapacityPolicy with InboxCapacityLimit = 1 for an inbox
3. Assign the policy to an agent (e.g., John)
4. Create 1 open conversation assigned to John (now at capacity)
5. Create a new unassigned conversation in the same inbox
6. Assign a team (containing John) to that conversation
7. Result: John gets assigned despite being at capacity
⏺ After the fix
Same steps 1–6.
7. Result: John is NOT assigned — conversation stays unassigned (no
agents with capacity available)


## 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/models/enterprise/inbox.rb

@@ -1,6 +1,7 @@
 module Enterprise::Inbox
   def member_ids_with_assignment_capacity
     return super unless enable_auto_assignment?
+    return filter_by_capacity(available_agents).map(&:user_id) if auto_assignment_v2_enabled?
 
     max_assignment_limit = auto_assignment_config['max_assignment_limit']
     overloaded_agent_ids = max_assignment_limit.present? ? get_agent_ids_over_assignment_limit(max_assignment_limit) : []

enterprise/app/models/enterprise/inbox_agent_availability.rb

@@ -21,7 +21,7 @@ module Enterprise::InboxAgentAvailability
   end
 
   def capacity_filtering_enabled?
-    account.feature_enabled?('assignment_v2') &&
+    account.feature_enabled?('advanced_assignment') &&
       account.account_users.joins(:agent_capacity_policy).exists?
   end
 

spec/enterprise/models/inbox_spec.rb

@@ -37,6 +37,103 @@ RSpec.describe Inbox do
     end
   end
 
+  describe 'member_ids_with_assignment_capacity with V2 capacity' do
+    let(:account) { create(:account) }
+    let(:v2_inbox) { create(:inbox, account: account, enable_auto_assignment: true) }
+    let(:agent_capacity_policy) { create(:agent_capacity_policy, account: account) }
+
+    let!(:agent1) { create(:user, account: account, role: :agent, auto_offline: false) }
+    let!(:agent2) { create(:user, account: account, role: :agent, auto_offline: false) }
+
+    before do
+      create(:inbox_member, inbox: v2_inbox, user: agent1)
+      create(:inbox_member, inbox: v2_inbox, user: agent2)
+
+      allow(OnlineStatusTracker).to receive(:get_available_users).and_return(
+        agent1.id.to_s => 'online',
+        agent2.id.to_s => 'online'
+      )
+    end
+
+    context 'when assignment_v2 is enabled with capacity policies' do
+      before do
+        account.enable_features('assignment_v2', 'advanced_assignment')
+        account.save!
+
+        create(:inbox_capacity_limit, agent_capacity_policy: agent_capacity_policy, inbox: v2_inbox, conversation_limit: 1)
+        agent1.account_users.find_by(account: account).update!(agent_capacity_policy: agent_capacity_policy)
+        agent2.account_users.find_by(account: account).update!(agent_capacity_policy: agent_capacity_policy)
+      end
+
+      it 'filters out agents at capacity' do
+        create(:conversation, inbox: v2_inbox, account: account, assignee: agent1, status: :open)
+
+        result = v2_inbox.member_ids_with_assignment_capacity
+        expect(result).to include(agent2.id)
+        expect(result).not_to include(agent1.id)
+      end
+
+      it 'filters out all agents when all are at capacity' do
+        create(:conversation, inbox: v2_inbox, account: account, assignee: agent1, status: :open)
+        create(:conversation, inbox: v2_inbox, account: account, assignee: agent2, status: :open)
+
+        expect(v2_inbox.member_ids_with_assignment_capacity).to be_empty
+      end
+
+      it 'skips V1 max_assignment_limit when V2 is enabled' do
+        v2_inbox.update(auto_assignment_config: { max_assignment_limit: 100 })
+
+        create(:conversation, inbox: v2_inbox, account: account, assignee: agent1, status: :open)
+
+        result = v2_inbox.member_ids_with_assignment_capacity
+        expect(result).not_to include(agent1.id)
+      end
+    end
+
+    context 'when assignment_v2 is enabled without capacity policies' do
+      before do
+        account.enable_features('assignment_v2', 'advanced_assignment')
+        account.save!
+      end
+
+      it 'returns all online agents' do
+        result = v2_inbox.member_ids_with_assignment_capacity
+        expect(result).to contain_exactly(agent1.id, agent2.id)
+      end
+    end
+
+    context 'when advanced_assignment is disabled (downgraded account with stale policies)' do
+      before do
+        account.enable_features('assignment_v2')
+        account.save!
+
+        create(:inbox_capacity_limit, agent_capacity_policy: agent_capacity_policy, inbox: v2_inbox, conversation_limit: 1)
+        agent1.account_users.find_by(account: account).update!(agent_capacity_policy: agent_capacity_policy)
+
+        create(:conversation, inbox: v2_inbox, account: account, assignee: agent1, status: :open)
+      end
+
+      it 'does not enforce capacity limits' do
+        result = v2_inbox.member_ids_with_assignment_capacity
+        expect(result).to include(agent1.id)
+      end
+    end
+
+    context 'when assignment_v2 is disabled (V1 path)' do
+      before do
+        v2_inbox.update(auto_assignment_config: { max_assignment_limit: 2 })
+      end
+
+      it 'uses V1 max_assignment_limit' do
+        create_list(:conversation, 2, inbox: v2_inbox, account: account, assignee: agent1, status: :open)
+
+        result = v2_inbox.member_ids_with_assignment_capacity
+        expect(result).not_to include(agent1.id)
+        expect(result).to include(agent2.id)
+      end
+    end
+  end
+
   describe 'audit log' do
     context 'when inbox is created' do
       it 'has associated audit log created' do