Wires the verified ROBDD entailment engine (generate/proof_chain,
716/716 wrong=0) into core chat serving. A propositional argument
('P1. P2. ... Therefore C.') is now comprehended, projected, and
decided end-to-end -- the first real working basic-logic workflow:
user question -> CORE decides -> articulated deterministic answer.
New: chat/deduction_surface.py (DEDUCTION composer, sibling to the
existing oov/narrative/example composer pattern), generate/proof_chain/
render.py (deterministic EntailmentTrace -> surface templates, no LLM),
tests/test_deduction_surface.py (15 tests incl. full propositional gold
corpus decided end-to-end across a multi-turn session, wrong=0).
Changed: core/config.py (deduction_serving_enabled flag, default off),
generate/intent.py (IntentTag.DEDUCTION, observability-only -- the core
classify_intent rule table is untouched so flag-off stays byte-identical),
chat/runtime.py (one flag-gated block in the existing pack/teaching/
partial/oov dispatcher).
Design notes (full detail in docs/research/deduction-serve-arc-phase1-
turn-spine-2026-07-23.md): the deduction check runs BEFORE generic intent
classification (never touches classify_intent's rule table) and BEFORE
the empty-vault gate (a live multi-turn probe caught turn-12 silently
falling through once the vault warmed -- pack/teaching/oov are cold-start-
only by design, deduction serving isn't). grounding_source='deduction' is
NOT registered in the closed, Workbench-coupled GroundingSource Literal
(cross-stack TS contract, inert for this arc's core-chat-only consumer,
documented as a deferred follow-up). Band v1 stays propositional-only --
categorical/syllogism arguments commit but honestly decline as
out-of-band; evals.syllogism.oracle is never imported (INV-25 intact).
[Verification]: smoke 180 passed; cognition 122 passed/1 skipped;
test_deduction_surface.py 15 passed; test_dispatch_trace.py +
test_oov_surface.py 26 passed; test_intent*.py 145 passed.
