Option 2 of the lane-isolation work. Mirrors the existing warm-path
hook into the cold-start branch (``gate_decision.fire`` ⇒ stub
response): after ``_maybe_pack_grounded_surface`` succeeds and the
result is pack- or teaching-grounded, build the same DiscoursePlan
and replace ``pack_surface`` with the rendered plan whenever it has
more than one move.
This closes the gap option 1 exposed: cold-start one-shot prompts
("Tell me about truth.", "Describe wisdom.", "Give me an example of
truth.") now produce deterministic multi-clause output without any
priming setup — the planner becomes the spine for grounded surfaces,
not a warm-only sidecar.
Gating discipline preserved:
* Engages only when pack_source_tag in {"pack", "teaching"}. Cases
routed to vault, none, or the discovery-signal disclosure are
untouched.
* BRIEF mode collapses to a single ANCHOR move which renders
byte-equivalent to the existing pack-grounded composer, so
flag-off cognition byte-identity is preserved.
* Empty bundles → empty plan → no surface change (planner is total).
A/B on multi_sentence_response (21 cases, public/v1):
flag off: multi=0.1429, primed_multi=0.0000, conn=0.0769
flag on : multi=0.5238, primed_multi=0.5000, conn=0.2308
Cold-start lift: multi +38pp, conn +15pp. Primed metric unchanged
(those cases already engaged the warm hook in step 5).
Sample cold-start surfaces flag-on:
* "Tell me about truth."
→ "Truth is a claim or state grounded by evidence and coherent
judgment. Furthermore, truth belongs to cognition.truth. In
turn, truth grounds knowledge."
* "Describe wisdom."
→ "Wisdom is sound judgment informed by knowledge and experience.
Furthermore, wisdom belongs to cognition.wisdom. In turn,
wisdom orders judgment."
* "Give me an example of truth."
→ "Truth is a claim or state grounded by evidence and coherent
judgment. In turn, truth grounds knowledge." (EXAMPLE mode:
anchor + relation, no support)
Gates all green:
* flag off: cognition eval byte-identical
- public 100/100/91.7/100, holdout 100/100/83.3/100
* smoke suite 67/67
* conversational_thread_coherence: 3 unwanted placeholders flag off
and flag on (no regression)
* 136/136 planner + grounding + intent + lane tests pass
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