feat: insrument captain v2 (#13439)

# Pull Request Template

## Description

Instruments captain v2

## 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.

Local testing:
<img width="864" height="510" alt="image"
src="https://github.com/user-attachments/assets/855ebce5-e8b8-4d22-b0bb-0d413769a6ab"
/>



## 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

---------

Co-authored-by: Shivam Mishra <scm.mymail@gmail.com>

spec/enterprise/services/captain/assistant/agent_runner_service_spec.rb

@@ -75,6 +75,7 @@ RSpec.describe Captain::Assistant::AgentRunnerService do
 
     it 'runs agent with extracted user message and context' do
       expected_context = {
+        session_id: "#{account.id}_#{conversation.display_id}",
         conversation_history: [
           { role: :user, content: 'Hello there', agent_name: nil },
           { role: :assistant, content: 'Hi! How can I help you?', agent_name: 'Assistant' },
@@ -306,6 +307,60 @@ RSpec.describe Captain::Assistant::AgentRunnerService do
     end
   end
 
+  describe '#add_usage_metadata_callback' do
+    it 'sets credits_used=false when handoff tool is used' do
+      service = described_class.new(assistant: assistant, conversation: conversation)
+      runner = instance_double(Agents::AgentRunner)
+      tool_complete_callback = nil
+      run_complete_callback = nil
+      span_class = Class.new do
+        def set_attribute(*); end
+      end
+      root_span = instance_double(span_class)
+      context_wrapper = Struct.new(:context).new({ __otel_tracing: { root_span: root_span } })
+
+      allow(ChatwootApp).to receive(:otel_enabled?).and_return(true)
+      allow(runner).to receive(:on_tool_complete) do |&block|
+        tool_complete_callback = block
+        runner
+      end
+      allow(runner).to receive(:on_run_complete) do |&block|
+        run_complete_callback = block
+        runner
+      end
+
+      service.send(:add_usage_metadata_callback, runner)
+
+      tool_complete_callback.call(Captain::Tools::HandoffTool.new(assistant).name, 'ok', context_wrapper)
+
+      expect(root_span).to receive(:set_attribute).with('langfuse.trace.metadata.credits_used', false)
+      run_complete_callback.call('assistant', nil, context_wrapper)
+    end
+
+    it 'sets credits_used=true when handoff tool is not used' do
+      service = described_class.new(assistant: assistant, conversation: conversation)
+      runner = instance_double(Agents::AgentRunner)
+      run_complete_callback = nil
+      span_class = Class.new do
+        def set_attribute(*); end
+      end
+      root_span = instance_double(span_class)
+      context_wrapper = Struct.new(:context).new({ __otel_tracing: { root_span: root_span } })
+
+      allow(ChatwootApp).to receive(:otel_enabled?).and_return(true)
+      allow(runner).to receive(:on_tool_complete).and_return(runner)
+      allow(runner).to receive(:on_run_complete) do |&block|
+        run_complete_callback = block
+        runner
+      end
+
+      service.send(:add_usage_metadata_callback, runner)
+
+      expect(root_span).to receive(:set_attribute).with('langfuse.trace.metadata.credits_used', true)
+      run_complete_callback.call('assistant', nil, context_wrapper)
+    end
+  end
+
   describe 'constants' do
     it 'defines conversation state attributes' do
       expect(described_class::CONVERSATION_STATE_ATTRIBUTES).to include(