Closes the sibling vacuity CMB-a surfaced: R3's evals/rate_oracle solver_refuses branch
accepted any fixture labelled non_integer_solution without checking the arithmetic, and the
solved branch never recomputed the gold. A curator could certify an arithmetically-impossible
refusal or a wrong gold (with a self-consistent answer key) as valid — the 'obligation that
can't meaningfully fail = decoration' case CLAUDE.md forbids.
Adds _canonical_outcome (independent reimplementation of the single-rate algebra WITH R3.2
conversion — NOT a call to generate.rate_comprehension.solver, which would be circular). The
validator now cross-checks every solved gold (== computed) and every solver_refuses reason
(genuine) against it, with dedicated meaningful-fail tests anchored on hand-written literals.
Also removes the dead determinism self-comparison.
R3 gold stays 13/13 valid (7/2/4); reader 9/0/4 unchanged; 26 oracle/reader tests pass.
Off-serving; serving + other organs untouched.
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