fix: enforce email limits for agent invitations

Atomically reserve Chatwoot Cloud account email capacity before sending new agent invitations, including bulk creation, and roll back with HTTP 429 when the limit is exhausted.

spec/controllers/api/v1/accounts/agents_controller_spec.rb

@@ -177,6 +177,22 @@ RSpec.describe 'Agents API', type: :request do
         expect(response.parsed_body['email']).to eq(params[:email])
         expect(account.users.last.name).to eq('NewUser')
       end
+
+      context 'when the account email limit is exhausted' do
+        before do
+          allow(ChatwootApp).to receive(:chatwoot_cloud?).and_return(true)
+          account.update!(limits: { 'emails' => 0 })
+        end
+
+        it 'does not create an agent' do
+          expect do
+            post "/api/v1/accounts/#{account.id}/agents", params: params, headers: admin.create_new_auth_token, as: :json
+          end.not_to change(User, :count)
+
+          expect(response).to have_http_status(:too_many_requests)
+          expect(response.parsed_body['error']).to eq('The daily email limit for this account has been reached')
+        end
+      end
     end
   end
 
@@ -211,6 +227,22 @@ RSpec.describe 'Agents API', type: :request do
 
         expect(response).to have_http_status(:ok)
       end
+
+      context 'when the account email limit is exhausted' do
+        before do
+          allow(ChatwootApp).to receive(:chatwoot_cloud?).and_return(true)
+          account.update!(limits: { 'emails' => 0 })
+        end
+
+        it 'does not create agents' do
+          expect do
+            post "/api/v1/accounts/#{account.id}/agents/bulk_create", params: bulk_create_params, headers: admin.create_new_auth_token
+          end.not_to change(User, :count)
+
+          expect(response).to have_http_status(:too_many_requests)
+          expect(response.parsed_body['error']).to eq('The daily email limit for this account has been reached')
+        end
+      end
     end
   end
 end