First rung of the combined-rate ladder, off-serving (imports no generate.derivation /
core.reliability_gate). Claims exactly: the combined-rate setup ruler is defined and
gold-valid. No reader/solver/wiring yet — no capability claim.
- generate/combined_rate_comprehension/: local RateUnit (decoupled from R3), CombinedRateProblem
(two-explicit-rates + per-query-slot guard; effective_rate = rate_a +/- rate_b; non-positive net
left to the solver, not the model).
- evals/combined_rate_oracle/: span-free signature (sum commutative / difference ordered) + a
NON-VACUOUS validator. 17 gold fixtures: 6 solved (full combine_mode x query grid), 4
solver_refuses, 7 reader_refuses (the complete refusal taxonomy + the 2x2 domain-entry grid).
Adversarial 5-lens verification returned fix_first; the validator now cross-checks every solved
gold and solver_refuses reason against the canonical arithmetic (_canonical_outcome) so a
mislabelled / arithmetically-impossible fixture is rejected (meaningful-fail per CLAUDE.md), with
dedicated tests. Added eff<0 and eff=0/time coverage fixtures; removed a dead determinism guard.
gold 17/17 valid; 25 oracle tests; R1/R2/R3 + router-hygiene + serving all unchanged.
Doc: docs/analysis/cmb-a-combined-rate-ruler-2026-06-08.md
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