# Multi-Sentence Response Eval Lane — Contract

**Lane:** `multi_sentence_response`
**Version:** v1
**Created:** 2026-05-19
**Status:** Red on creation — measurement substrate for compositional surface.

## What this lane measures

Whether `ChatRuntime` can emit a response that is more than a single
sentence when the prompt structurally calls for elaboration
("Explain X", "Tell me about X", "Describe X", "Walk me through X").

Currently every pack-grounded surface is a single sentence emitted
by `_frame_gloss`.  NARRATIVE and EXAMPLE intents already compose
multi-clause output via teaching chains, so they are tested here too
as the *only* multi-sentence-capable code path.

## Per-case predicates

| Predicate | Definition |
|---|---|
| `sentence_count_>=_2`   | the substantive surface contains at least 2 terminated sentences (`.`, `?`, `!`) |
| `each_sentence_>=_4_tokens` | every sentence has ≥ 4 alphabetic tokens (no fragments) |
| `connective_present`    | the surface contains at least one connective (`and`, `because`, `therefore`, `which`, `since`, `also`, `furthermore`, `however`, `consequently`) — only enforced when `expects_connective=true` |
| `not_just_provenance_tag` | sentence_count counts BEFORE trailing provenance / trust-boundary tails (`pack-grounded (…).`, `No session evidence yet.`) are treated as real sentences |
| `grounded`              | `grounding_source` ∈ {pack, teaching} |
| `subject_named`         | the prompt's subject lemma appears in the surface |

## Scoring rubric

```text
articulate_sentence_rate   = cases with >=2 sentences AND grounded in {pack, teaching} / total
disclosure_sentence_rate   = cases with >=2 sentences AND grounded in {oov, refusal, none} / total
unarticulate_rate          = cases with <2 sentences / total
multi_sentence_rate        = cases_with_>=2_sentences / total_cases   # continuity metric
non_fragment_rate          = cases_where_every_sentence_>=4_tokens / total_cases
connective_present_rate    = cases_with_connective / cases_expecting_connective
primed_cases               = cases_where_priming_prompts_engaged
primed_multi_sentence_rate = primed_cases_with_>=2_sentences / primed_cases
```

**Doctrine-correct headline:** `articulate_sentence_rate`.

`multi_sentence_rate` is kept for continuity but is misleading on its own:
OOV teaching-invitation surfaces ("I don't know that yet — can you teach
me?") and refusal disclosures ("I don't know — insufficient grounding
for that yet.") are categorically multi-sentence by template, not by
articulation.  They count toward `disclosure_sentence_rate`, never
`articulate_sentence_rate`.

The decomposition is total:
`articulate + disclosure + unarticulate = 1.0` (modulo rounding).

## Priming (warm-path measurement)

A case may carry an optional `priming_prompts: [str, ...]` array.  The
runner runs each priming prompt on the same `ChatRuntime` instance
before the scored prompt, discards their responses, and then measures
the scored prompt.  This isolates code paths that engage only on the
warm vault/pack/teaching path (e.g. the discourse planner hook at
`chat/runtime.py`) from cold-start one-shot paths.

`primed_multi_sentence_rate` reports only on primed cases, so cold
cases never inflate or depress it.  The aggregate
`multi_sentence_rate` includes both.

## Doctrine constraints

- The trailing provenance / trust-boundary tail is structural, not a real
  sentence — predicate logic strips it before counting.
- Dotted semantic-domain atoms (`cognition.truth`, `logos.core`) are not
  sentence boundaries by themselves.  A terminal mark counts as a boundary
  only when it is followed by a new uppercase/digit sentence opener or the
  end of the substantive surface.
- No LLM judge.  Pure structural counting.
- Red-on-creation expected: only NARRATIVE / EXAMPLE / cross-pack /
  composed_surface code paths can possibly satisfy `sentence_count_>=_2`
  today.