Fix: Improve serialization of completions/responses in Agents SDK instrumentation

[devin-ai-integration]

Fix: Improve serialization of completions/responses in Agents SDK instrumentation

This PR fixes the serialization of completions/responses in the Agents SDK OpenTelemetry instrumentation. Instead of truncating or printing the string representation of the object, it now extracts specific fields referenced in the semconv definitions.

Changes

• Added model_as_dict() helper function to safely convert response objects to dictionaries
• Updated _export_span() method to extract specific fields from response objects:
  • Model information
  • Response ID
  • System fingerprint
  • Token usage metrics
  • Completion content and metadata
  • Function/tool call information

Benefits

• Increases the number of attributes from 2 to 13+ for each response
• Preserves structured data instead of truncating to string
• Maintains compatibility with different response object formats
• Follows semantic convention standards

Link to Devin run: https://app.devin.ai/sessions/480cc142d3b94f70828c01815f3622ef

This is a draft PR for exploring potential solutions to the problem.

[devin-ai-integration]

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[devin-ai-integration]

Closing in favor of PR #845 which contains only the essential serialization fix changes