Competition tests t1a_thinking_true and t1c_thinking_default both expect
reasoning_content > 0. Sub509 returned reasoning[0] for both (1.54s each).
Root cause: Qwen3.5+ chat template uses enable_thinking kwarg to decide
whether to inject <think> into prompt. Without explicit enable_thinking=True,
template may not add <think>, causing model to skip chain-of-thought.
Competitor Sub168: t1a reasoning[541] (7.85s), t1c reasoning[411] (6.29s).
Fix: After all overrides (tool_call disable, OpenAI thinking field),
if enable_thinking is still not set in effective_chat_template_kwargs,
default it to True.
Source pattern: CCCL interpreted_execution_policy.cuh — default policy
mapping when no explicit override is specified.
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