fix: playground captain v2 scenarios (#13747)

# Pull Request Template

## Description

Playground now uses v2. It was only wired to use v1. Traces get `source:
playground` on langfuse when playground has been used.

## Type of change

- [x] New feature (non-breaking change which adds functionality)

## How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide
instructions so we can reproduce. Please also list any relevant details
for your test configuration.

locally and specs
<img width="1806" height="1276" alt="image"
src="https://github.com/user-attachments/assets/41ef4eb3-52b1-4b8e-9a4f-e8510c90cb39"
/>


## Checklist:

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

spec/enterprise/controllers/api/v1/accounts/captain/assistants_controller_spec.rb

@@ -259,10 +259,12 @@ RSpec.describe 'Api::V1::Accounts::Captain::Assistants', type: :request do
         message_content: 'Hello assistant',
         message_history: [
           { role: 'user', content: 'Previous message' },
-          { role: 'assistant', content: 'Previous response' }
+          { role: 'assistant', content: 'Previous response', agent_name: 'billing_scenario' }
         ]
       }
     end
+    let(:chat_service) { instance_double(Captain::Llm::AssistantChatService) }
+    let(:agent_runner_service) { instance_double(Captain::Assistant::AgentRunnerService) }
 
     context 'when it is an un-authenticated user' do
       it 'returns unauthorized' do
@@ -274,11 +276,14 @@ RSpec.describe 'Api::V1::Accounts::Captain::Assistants', type: :request do
       end
     end
 
-    context 'when it is an agent' do
-      it 'generates a response' do
-        chat_service = instance_double(Captain::Llm::AssistantChatService)
-        allow(Captain::Llm::AssistantChatService).to receive(:new).with(assistant: assistant).and_return(chat_service)
+    context 'when captain v2 is disabled' do
+      it 'generates a response with the legacy assistant chat service' do
+        allow(Captain::Llm::AssistantChatService).to receive(:new).with(
+          assistant: assistant,
+          source: 'playground'
+        ).and_return(chat_service)
         allow(chat_service).to receive(:generate_response).and_return({ content: 'Assistant response' })
+        expect(Captain::Assistant::AgentRunnerService).not_to receive(:new)
 
         post "/api/v1/accounts/#{account.id}/captain/assistants/#{assistant.id}/playground",
              params: valid_params,
@@ -292,14 +297,15 @@ RSpec.describe 'Api::V1::Accounts::Captain::Assistants', type: :request do
         )
         expect(json_response[:content]).to eq('Assistant response')
       end
-    end
 
-    context 'when message_history is not provided' do
       it 'uses empty array as default' do
         params_without_history = { message_content: 'Hello assistant' }
-        chat_service = instance_double(Captain::Llm::AssistantChatService)
-        allow(Captain::Llm::AssistantChatService).to receive(:new).with(assistant: assistant).and_return(chat_service)
+        allow(Captain::Llm::AssistantChatService).to receive(:new).with(
+          assistant: assistant,
+          source: 'playground'
+        ).and_return(chat_service)
         allow(chat_service).to receive(:generate_response).and_return({ content: 'Assistant response' })
+        expect(Captain::Assistant::AgentRunnerService).not_to receive(:new)
 
         post "/api/v1/accounts/#{account.id}/captain/assistants/#{assistant.id}/playground",
              params: params_without_history,
@@ -313,5 +319,53 @@ RSpec.describe 'Api::V1::Accounts::Captain::Assistants', type: :request do
         )
       end
     end
+
+    context 'when captain v2 is enabled' do
+      before do
+        account.enable_features('captain_integration_v2')
+      end
+
+      it 'generates a response with the agent runner service' do
+        allow(Captain::Assistant::AgentRunnerService).to receive(:new).with(
+          assistant: assistant,
+          source: 'playground'
+        ).and_return(agent_runner_service)
+        allow(agent_runner_service).to receive(:generate_response).and_return({ response: 'Assistant response' })
+        expect(Captain::Llm::AssistantChatService).not_to receive(:new)
+
+        post "/api/v1/accounts/#{account.id}/captain/assistants/#{assistant.id}/playground",
+             params: valid_params,
+             headers: agent.create_new_auth_token,
+             as: :json
+
+        expect(response).to have_http_status(:success)
+        expect(agent_runner_service).to have_received(:generate_response).with(
+          message_history: valid_params[:message_history] + [{ role: 'user', content: valid_params[:message_content] }]
+        )
+        expect(json_response[:response]).to eq('Assistant response')
+      end
+
+      it 'does not duplicate the latest user message if it is already in history' do
+        params_with_latest_message = {
+          message_content: 'Hello assistant',
+          message_history: [{ role: 'user', content: 'Hello assistant' }]
+        }
+        allow(Captain::Assistant::AgentRunnerService).to receive(:new).with(
+          assistant: assistant,
+          source: 'playground'
+        ).and_return(agent_runner_service)
+        allow(agent_runner_service).to receive(:generate_response).and_return({ response: 'Assistant response' })
+
+        post "/api/v1/accounts/#{account.id}/captain/assistants/#{assistant.id}/playground",
+             params: params_with_latest_message,
+             headers: agent.create_new_auth_token,
+             as: :json
+
+        expect(response).to have_http_status(:success)
+        expect(agent_runner_service).to have_received(:generate_response).with(
+          message_history: params_with_latest_message[:message_history]
+        )
+      end
+    end
   end
 end