ADR-0184 S1 (state/bind.py, state/change.py) landed the reusable referent and
change-cue helpers. S2 adds the first explicit state-transition substrate and
routes both accumulation readings through it:
- state/model.py frozen SET/GAIN/LOSS transition model over one entity/unit
StateKey, with structural validation (closed op set; unit is a
str with "" = unitless, mirroring the extractor's Quantity.unit
contract; entity optional, mirroring leading_subject_token).
- state/ledger.py build_accumulation_ledger() — the proven single-referent
gain/loss reading, expressed as a SemanticLedger.
- state/replay.py replay_accumulation_ledger() — the only bridge to
GroundedDerivation; refuses any non-accumulation ledger shape
(non-SET start, cross-key mutation).
accumulate.py's _build_accumulation / _build_accumulation_anchor_skip now build a
ledger and replay it instead of constructing the arithmetic chain inline; the
public compose_accumulation()/accumulation_candidates() surfaces are unchanged.
Behavior-equivalent: a byte-for-byte differential over 937 real GSM8K problems
(accumulation_candidates, compose_accumulation, pooled_candidates, resolve_pooled)
shows 0 differences vs main. Semantic worlds never commit directly — replay emits
GroundedDerivation and verify.py / pool.py remain the sole authority. Sealed: no
serving/runtime/chat import; no CLAIMS or eval-lane-SHA movement.
Refs ADR-0184 section 7 (S2).
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