build-rag-evallisted

# Skill: Build RAG eval A RAG system without an offline eval is shipping on vibes (§3 #3). ## Step 1 — Build the judgment set Representative queries with the relevant passages and ideal answers labeled (§3 #3). ## Step 2 — Measure retrieval Recall@k and precision@k via `ai_rag_engineering_calc.py retrieval-eval` (§3 #1 #3). ## Step 3 — Measure generation Faithfulness (grounded?) and answer-relevance (addresses query?) (§3 #3 #7). ## Step 4 — Baseline before changing Record the baseline; every change reports a before/after delta — no eval, no ship (§3 #3). ## Output An eval harness with recall@k, precision@k, faithfulness, answer-relevance, and a baseline. Traverse Tree 1 in the decision-trees file.