Add BFCL cohesive namespace candidate ablation

[SonAIengine]

Summary

• add --cohesive-namespace-candidates to BFCL model loop and sweep runners
• keep raw retrieval unchanged while compressing the LLM-facing tools_presented set for multi-action retrieved queries with a cohesive dotted namespace family
• document the first qwen3.6-27B small smoke where the xgen-0.27 milestone gate passes

qwen3.6-27B Smoke Evidence

Via go165 vLLM qwen3.6-27b, category limit 5, row/retrieved k=5.

Artifact: /tmp/gtc-bfcl-qwen027-cohesive-smoke-v2.json

• row exact: 1.00
• retrieved exact: 0.95
• retrieval recall: 1.00
• row-source preservation: 0.95
• parallel_multiple exact: 0.80
• milestone gate: pass

Hard-case bundle: /tmp/gtc-bfcl-qwen027-cohesive-hardcases-v2

• cases: 1
• remaining failure: parallel_multiple_4 integral sibling ambiguity

This is small-smoke evidence, not a publishable full BFCL number. Next promotion step is a failure-subset run and then a larger sweep.

Validation

• poetry run ruff check .
• poetry run ruff format --check .
• poetry run pytest tests/ -q -> 952 passed, 3 skipped

[SonAIengine]

Closing this internal stacked PR as superseded by the current main branch. The branch is preserved for history.