test(u6): add L4 real-LLM smoke test for ReAct tool-use prompt
Manual smoke test verifying U4 L0 prompt rule rearrangement under real
LLM calls (bailian-coding/qwen3.7-plus). 5 probe queries covering
external_info / realtime_data / multi_step / realtime_simple / no_tool.
Results:
- Probe #1 external_info: PASS (8 web_search calls, 99.9s)
- Probe #2 realtime_data: ERROR (120s timeout, not LLM refusal)
- Probe #3 multi_step: PASS (8 web_search calls, 62.6s)
- Probe #4 realtime_data_simple: PASS (3 web_search calls, 23.8s)
- Probe #5 no_tool_escape_hatch: PASS (0 tool calls, direct answer, 4.2s)
Verdict: 3/4 tool-call pass (>=3/4 threshold) + 1/1 direct pass
Bug 2 status upgraded to 'L4 verified'.
Plan Progress table updated: U6 done, U7 done.
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