fix: typo in metadata key in captain v2 (#13558)

# Pull Request Template

## Description

## Type of change

typo fix

## 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.


## 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

enterprise/app/services/captain/assistant/agent_runner_service.rb

@@ -189,8 +189,8 @@ class Captain::Assistant::AgentRunnerService
     root_span = context_wrapper&.context&.dig(:__otel_tracing, :root_span)
     return unless root_span
 
-    credits_used = !context_wrapper.context[:captain_v2_handoff_tool_called]
-    root_span.set_attribute(format(ATTR_LANGFUSE_METADATA, 'credits_used'), credits_used)
+    credit_used = !context_wrapper.context[:captain_v2_handoff_tool_called]
+    root_span.set_attribute(format(ATTR_LANGFUSE_METADATA, 'credit_used'), credit_used.to_s)
   end
 
   def add_agent_thinking_callback(runner)

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

@@ -308,7 +308,7 @@ RSpec.describe Captain::Assistant::AgentRunnerService do
   end
 
   describe '#add_usage_metadata_callback' do
-    it 'sets credits_used=false when handoff tool is used' do
+    it 'sets credit_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
@@ -333,11 +333,11 @@ RSpec.describe Captain::Assistant::AgentRunnerService do
 
       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)
+      expect(root_span).to receive(:set_attribute).with('langfuse.trace.metadata.credit_used', 'false')
       run_complete_callback.call('assistant', nil, context_wrapper)
     end
 
-    it 'sets credits_used=true when handoff tool is not used' do
+    it 'sets credit_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
@@ -356,7 +356,7 @@ RSpec.describe Captain::Assistant::AgentRunnerService do
 
       service.send(:add_usage_metadata_callback, runner)
 
-      expect(root_span).to receive(:set_attribute).with('langfuse.trace.metadata.credits_used', true)
+      expect(root_span).to receive(:set_attribute).with('langfuse.trace.metadata.credit_used', 'true')
       run_complete_callback.call('assistant', nil, context_wrapper)
     end
   end