tests: add unit tests for Responses API

[enyst]

This PR adds focused unit tests validating the new Responses API functionality introduced on the response branch.

What’s covered

• Message serialization for Responses:
  • system → instructions string (concatenation with separators)
  • user → input_text and input_image (vision gating respected)
  • assistant → output_text content and function_call items (fc_ id prefix)
  • tool → function_call_output items with matching call_id
• Message.from_llm_responses_output() parsing:
  • Aggregates assistant output_text
  • Normalizes function_call to MessageToolCall
  • Maps typed reasoning to ReasoningItemModel
• LLM._normalize_responses_kwargs() policy:
  • temperature=1.0, tool_choice="auto"
  • include encrypted reasoning when enabled
  • store defaults False; reasoning defaults to detailed summary
  • max_output_tokens passthrough
• LLM.responses() integration (mocked litellm.responses):
  • End-to-end test returns proper assistant Message and records usage in telemetry
• ToolBase.to_responses_tool():
  • Ensures type=function, strict=True, and parameters schema present

Files added

• tests/sdk/llm/test_responses_serialization.py
• tests/sdk/llm/test_responses_parsing_and_kwargs.py
• tests/sdk/tool/test_to_responses_tool.py

Notes

• No source changes; tests use current litellm/openai typed models available in this repo.
• Full test suite: 1487 passed locally.

Co-authored-by: openhands openhands@all-hands.dev

@enyst can click here to continue refining the PR

[openhands-ai]

Looks like there are a few issues preventing this PR from being merged!

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If you'd like me to help, just leave a comment, like

@OpenHands please fix the failing actions on PR #634 at branch `chore/add-responses-tests`

Feel free to include any additional details that might help me get this PR into a better state.

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