Evaluating the Brain — careful, fair grading

The Brain answers via the brain_chatbot agentic API; you grade each answer against a ground-truth expected_response in the question bank. Grading is LLM-as-judge, and the whole value of this skill is doing it carefully and fairly — neither generous nor harsh, and never mistaking thoroughness for hallucination.

The two rules that define "careful" here

Rule 1 — Curate the question set first: drop non-questions

A two-word "question" is not a good question and must not be scored. Before grading, filter the bank and set aside (don't delete — mark excluded with a reason) any item that is:

• Too short / not a real question — e.g. two-word fragments, a bare code or term with no interrogative intent ("PO approval", "GRN status").
• Malformed or ambiguous — no answerable proposition; the grader can't tell what a correct answer would even be.
• Out of Layer-1 scope — needs live transaction/deployment/telemetry data (Tier-2/Tier-3), which the documentation Brain deliberately does not hold.
• EXPECTED_UNVERIFIABLE — the expected_response itself is wrong or unanswerable (a test-bank quality issue, not a Brain failure).

Report the excluded set separately with counts by reason, and score only the clean set. A rough heuristic for "too short": fewer than ~4 meaningful words and no clear ask — but use judgment, not just a word count; a short but well-formed question ("What does GRN stand for?") stays in.

Rule 2 — A superset answer is CORRECT, not a hallucination

The Brain often answers more comprehensively than the terse ground truth. That is good, not a failure. Grade on informational equivalence of the important points, not on length or format:

• If the answer contains all the important/main points of the expected_response and those points are correct, the answer is correct — even if the ground truth is only a subset of what the answer says.
• Extra correct detail is never penalized and is never a hallucination.
• Hallucination = inventing new things that are not there — asserting a fact (a name, code, value, relationship, rule) that is not supported by the Brain or the sources. Only fabrication counts. Before flagging a hallucination, try to confirm the claimed fact is actually absent from the Brain (grep/read) — if it's present, it's not a hallucination.
• This is English-language semantic matching, so be careful: paraphrase, synonyms, reordering, and different-but-equivalent phrasings all count as matches. Do not require verbatim string overlap. Conversely, a fluent answer that misses a load-bearing expected point, or gets one wrong, is not "correct" no matter how polished.

Put simply: correct = (all important expected points present and right) AND (nothing fabricated). Extra truth is a bonus; missing an important point is a miss; invented facts are the only hallucination.

The grading workflow

1. Load & curate the bank (Rule 1). Keep a clean set + an excluded set with reasons.
2. Get the Brain's answer for each kept question via brain_chatbot (two-tier: unlimited tool-rounds first, retry capped at 25 on error/limit). Capture brain_answer + brain_sources.
3. Judge each answer against expected_response on the 0–5 scale (see references/rubric.md): 5 fully correct & complete · 4 complete, trivial omission · 3 core present, some specifics missing · 2 topic present, major specifics missing · 1 barely any expected content · 0 absent or incorrect. Apply Rule 2 while scoring: a superset answer whose important points match earns a 5 (or 4 for a trivial omission) — the ground truth being a subset does not cap the score.
4. Derive the verdict: FULL = score ≥ 4, PARTIAL = 2–3, MISSING = 0–1; answerable = score ≥ 2.
5. Set the flags: hallucination (bool — only true for fabricated facts, per Rule 2), gap_present (a genuine Brain knowledge gap, not a mere retrieval/surfacing miss), and the gap_category (see rubric).
6. Aggregate & report — FULL% / answerable% / mean score, plus the excluded set, gap categories, and any regressions vs the prior run.

Grading discipline (do these while judging)

• Judge on informational equivalence, not path/format. The bank's source_reference cites an idealized kb/<COMP>/layer*.json scheme that does not physically exist in the delivered Brain (which holds the same content as markdown pages + JSONL registers + journey JSON). A "wrong file cited" is not wrong if the fact is present. Use the GT→Brain layer mapping.
• Verify before you accept; refute before you fail. Before accepting a claim as correct, confirm the fact is actually in the Brain (catches hallucination). Before marking something missing, actively try to refute the gap (grep brain/, read the cited pages) — many "gaps" are the chatbot picking the wrong page (RETRIEVAL_ONLY), not absent knowledge.
• Check the Sources section. A good answer ends with a Sources list of repo-relative paths it actually read, and cites component/activity/SP/status/slot codes exactly. Missing or fabricated citations are a real defect.
• Honour the standing traps. e.g. GRN = Goods Return Note (return to supplier), not the receipt (GR) — any answer conflating them fails, however fluent. ARM cross-check: claims sourced only from Application Reference Manuals (ARM = intended behaviour, possibly stale) must be verified against a non-ARM (SP-derived) source; on conflict the SP-derived layer wins.
• Scrutinize functional-prose answers hardest. Technical categories (API, UI, schema, CIM) score high; functional categories (entity relationships, error messages, SP chains, computation, reporting) are where imprecise-but-fluent answers slip through — grade those most skeptically.
• Be aware of judge variance. Borderline FULL↔PARTIAL calls carry grader subjectivity; when unsure, read the actual Brain page rather than guessing, and record one precise sentence of gap_description so a human reviewer can calibrate.

What each graded record should contain

id, score(0-5), verdict, answerable, brain_answer, brain_sources, hallucination(bool), gap_present(bool), gap_category, gap_severity, correct_facts, missing_or_wrong, suggested_resolution. Plus, for excluded items: excluded(true), exclusion_reason.

Full rubric, gap-category enum, worked examples, and the bank layout are in the references:

• references/rubric.md — the 0–5 scale, verdict banding, gap categories, hallucination vs superset examples, the judge discipline in full.
• references/question-bank.md — where the bank lives, its fields and facets, the train/validation/test splits, the historical scores, and known eval gaps.

Report structure

ALWAYS produce:

# Layer-1 Eval — <run id / date>
## Curation
- kept: N   excluded: M  (by reason: too-short K, out-of-scope K, unverifiable K, malformed K)
## Headline (clean set)
- mean score X.XX/5 · FULL P% · answerable P% · hallucinations H (fabricated facts only)
## Breakdown
- by difficulty, by category/BPC
## Gaps (genuine knowledge gaps only)
- by gap_category, top items with one-sentence descriptions + suggested_resolution
## Regressions vs prior run
- any previously-FULL question now PARTIAL/MISSING (investigate — see reindex-brain Regression Gate)