Closes the last unarticulate cases on the multi_sentence_response
lane. Two complementary changes:
1. ``generate/discourse_planner.py``
* ``ResponseMode.WALKTHROUGH`` budget lifted from (1, 1) to
(1, 4): 1 anchor + up to 3 hops along the teaching-chain graph,
final hop becomes CLOSURE.
* New ``_plan_walkthrough`` selector walks (subject, *, object) →
(object, *, *) starting from the anchor; cycle-safe via the
existing used-fact set; bounded by ``_WALKTHROUGH_MAX_HOPS=3``.
* New ``_plan_walkthrough_fallback`` — when no teaching chain is
rooted on the anchor, emit ANCHOR + (SUPPORT) rather than
fabricating walk steps. Plan retains ``mode=WALKTHROUGH`` so
callers detect "attempted walkthrough, degraded honestly".
2. ``generate/intent.py``
* New classifier rule: ``^walk\s+(?:me\s+)?through\s+`` →
``IntentTag.DEFINITION``. Same orthogonality discipline as the
``Explain X`` rule: ``ResponseMode.WALKTHROUGH`` carries the
walk depth on its own axis.
13 new tests pin: walk shape (ANCHOR + RELATION* + CLOSURE), the
walk invariant (each teaching hop's subject = prior hop's object),
the 4-move cap, the fallback shape on absent chains, fallback mode
retention, cycle-safety against (A→B→A) cycles, and determinism.
Lane re-measurement (24 cases, multi_sentence_response public/v1):
flag off: articulate=0.0833, disclosure=0.1667, unarticulate=0.7500
flag on : articulate=1.0000, disclosure=0.0000, unarticulate=0.0000
The two previously-unarticulate WALKTHROUGH cases ("Walk me through
inference.", "Walk me through recall.") now engage the planner and
render as deterministic teaching-chain walks:
"Inference is a conclusion drawn from premises by reasoning.
Inference requires evidence."
"Recall is to retrieve a stored state from memory.
Recall reveals memory."
Each surface is grounded entirely in pack glosses and reviewed
teaching chains — no fabricated walk steps.
Critical gates all green:
* flag off cognition byte-identical:
public 100/100/91.7/100, holdout 100/100/83.3/100
* smoke suite 67/67
* 91/91 planner tests pass (contract / behavior / compound / helper
/ render / walkthrough)
The 0.875 connective_present_rate remaining flag-on (3 cases without
expected connectives) is the only gap left, and it's now a render-
template question rather than a planner gap.
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