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.
Option A (text-faithful): RateProblem gains time_unit (the duration's ORIGINAL unit; time stays int; defaults to the rate denominator). The SOLVER converts via convert_time -> exact Fraction -> int-or-refuse(non_integer); Fraction never leaves the solver, no floats. The reader accepts a convertible (minute<->hour) duration mismatch (keeps original time_unit); a non-convertible one still refuses rate_unit_mismatch. Signature includes time_unit ('30 minutes' != '30 hours').
Gold: r3-09 flips reader_refuses -> SOLVED (60 mph for 30 min = 30 mile, exact 1/2 hour; distractor 1800 rejected); new r3-13 non-convertible (3 gallons) stays rate_unit_mismatch. R3 gold 13/13; reader 9/0/0 -> answers 7/0/6 (setup_correct 8->9). Failure-family: rate_unit_mismatch now non-convertible-only -> still unsupported_rate_duration proposal surface; router-hygiene invariant stays green; R1 7/0/3, R2 10/0/0 unchanged. 119-test smoke green incl. invariants. Off-serving, no float path.
