fix(qwen): always send explicit enable_thinking in chat_template_kwargs

[LESdylan]

Problem

skillopt/model/qwen_backend.py only attached chat_template_kwargs when enable_thinking was true:

if config.enable_thinking:
    payload["chat_template_kwargs"] = {"enable_thinking": True}

With enable_thinking=false the key was omitted entirely, so whether Qwen thinking mode ran was decided by the vLLM server / chat-template default — which varies across deployments and makes results hard to reproduce. This is exactly point 3 of #90, where @Huangzisu confirmed the reported results used client-side enable_thinking=false and that the code would be adjusted.

Change

Always send an explicit boolean:

payload["chat_template_kwargs"] = {"enable_thinking": bool(config.enable_thinking)}

This matches the MiniMax backend, which already sends the flag unconditionally (minimax_backend.py).

Tests

Updated the two tests that pinned the omit-when-disabled behavior to assert an explicit {"enable_thinking": False} instead. Full suite: 165 passed, 5 skipped.

Ref #90

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[Yif-Yang]

Thanks for this fix — the behavior is valuable and we would like to land it through your original PR so your contribution remains fully attributed.

Current main has since merged #128, so this branch now conflicts in qwen_backend.py. Could you please rebase onto the latest main and resolve it by preserving both behaviors?

• Keep fix(qwen): support reasoning-model params (max_completion_tokens, omit temperature) #128 handling for reasoning models: max_completion_tokens and omission of temperature where required.
• Always send chat_template_kwargs={"enable_thinking": bool(config.enable_thinking)}, including the explicit false case from this PR.
• Keep the existing optimizer/target role-specific configuration.

We tested that combined resolution locally: the Qwen tests and the full suite pass. Suggested verification:

pytest tests/test_qwen_backend.py -q
pytest tests/ -q

The CLA check is also still waiting for your response to the policy bot. Once rebased, CLA-complete, and green, this should be a good merge candidate. Please ping us after updating; we are happy to re-review promptly.