feat: langfuse logging improvements (#13534)

Langfuse logging improvements

## Description

Please include a summary of the change and issue(s) fixed. Also, mention
relevant motivation, context, and any dependencies that this change
requires.
Fixes # (issue)
For reply suggestion: the errors are being stored inside output field,
but observations should be marked as errors.
For assistant: add credit_used metadata to filter handoffs from
ai-replies
For langfuse tool call: add `observation_type=tool`

## Type of change

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

before:
<img width="1028" height="57" alt="image"
src="https://github.com/user-attachments/assets/70f6a36e-6c33-444c-a083-723c7c9e823a"
/>

after:
<img width="872" height="69" alt="image"
src="https://github.com/user-attachments/assets/1b6b6f5f-5384-4e9c-92ba-f56748fec6dd"
/>

`credit_used` to filter handoffs from AI replies that cause credit usage
<img width="1082" height="672" alt="image"
src="https://github.com/user-attachments/assets/90914227-553a-4c03-bc43-56b2018ac7c1"
/>


set `observation_type` to `tool`
<img width="726" height="1452" alt="image"
src="https://github.com/user-attachments/assets/e639cc9b-1c6c-4427-887e-23e5523bf64f"
/>


## 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
- [ ] 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

lib/integrations/llm_instrumentation.rb

@@ -37,6 +37,7 @@ module Integrations::LlmInstrumentation
       result = yield
       executed = true
       span.set_attribute(ATTR_LANGFUSE_OBSERVATION_OUTPUT, result.to_json)
+      set_error_attributes(span, result) if result.is_a?(Hash)
       result
     end
   rescue StandardError => e
@@ -50,9 +51,11 @@ module Integrations::LlmInstrumentation
     return yield unless ChatwootApp.otel_enabled?
 
     tracer.in_span(format(TOOL_SPAN_NAME, tool_name)) do |span|
+      span.set_attribute(ATTR_LANGFUSE_OBSERVATION_TYPE, 'tool')
       span.set_attribute(ATTR_LANGFUSE_OBSERVATION_INPUT, arguments.to_json)
       result = yield
       span.set_attribute(ATTR_LANGFUSE_OBSERVATION_OUTPUT, result.to_json)
+      set_error_attributes(span, result) if result.is_a?(Hash)
       result
     end
   end

lib/integrations/llm_instrumentation_constants.rb

@@ -26,6 +26,7 @@ module Integrations::LlmInstrumentationConstants
   ATTR_LANGFUSE_METADATA = 'langfuse.trace.metadata.%s'
   ATTR_LANGFUSE_TRACE_INPUT = 'langfuse.trace.input'
   ATTR_LANGFUSE_TRACE_OUTPUT = 'langfuse.trace.output'
+  ATTR_LANGFUSE_OBSERVATION_TYPE = 'langfuse.observation.type'
   ATTR_LANGFUSE_OBSERVATION_INPUT = 'langfuse.observation.input'
   ATTR_LANGFUSE_OBSERVATION_OUTPUT = 'langfuse.observation.output'
 end

lib/integrations/llm_instrumentation_spans.rb

@@ -39,6 +39,7 @@ module Integrations::LlmInstrumentationSpans
 
     tool_name = tool_call.name.to_s
     span = tracer.start_span(format(TOOL_SPAN_NAME, tool_name))
+    span.set_attribute(ATTR_LANGFUSE_OBSERVATION_TYPE, 'tool')
     span.set_attribute(ATTR_LANGFUSE_OBSERVATION_INPUT, tool_call.arguments.to_json)
 
     @pending_tool_spans ||= []