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.
generate/rate_comprehension/conversion.py: convert_time(value, from_unit, to_unit) -> Fraction for known time units (minute<->hour), exact rational (fractions.Fraction), NO floats. is_convertible gates it. 30 minute -> Fraction(1,2) hour; non-time/non-convertible (minute<->mile, dollar<->hour) raises ConversionError so the caller still refuses rate_unit_mismatch. Tiny: only minute<->hour in v1 (length/currency/compound deferred). 6 tests incl. never-a-float guard.
classify_r3 normalizes the rate reader into a ComprehensionAttempt; route_setup now tries R1/R2/R3 (same exactly-one-setup_correct rule); the pass manager solves+verifies a routed r3_rate setup (solve_rate + reused answer-choice verifier); unsupported_temporal_state dropped from the unsupported-family set so temporal_state -> REFUSED_KNOWN_BOUNDARY. Organ gains r3_rate.
Terminal matrix (verified): 6 solved->SOLVED_VERIFIED; rate_unit_mismatch+combined_rates->PROPOSAL_EMITTED(unsupported_rate_duration); non_integer/missing_time/temporal->REFUSED_KNOWN_BOUNDARY; exactly 2 proposals (the rate-like gaps only).
REGRESSION CAUGHT+FIXED: R3's reader returned missing_rate (a substantive boundary) on non-rate R2 text, blocking r2-011's legitimate missing_total_count proposal via boundary-first. Fix: missing_rate only when a duration is present; else not_rate_shaped -> input_shape (not-my-domain) — same discipline as the N6 category_pair_not_found fix. r2-011 proposes again; R1/R2 unaffected. R1 7/0/3, 15-case 15/0/0, R2 10/0/0, R3 8/0/0 unchanged; off-serving; 121-test smoke green incl. invariants + idle contract suites.
generate/rate_comprehension/solver.py: solve_rate computes the one unknown — quantity=rate×time (always integer), rate=quantity÷time, time=quantity÷rate (exact division or REFUSE non_integer_solution, never rounds). Confirms compound-unit composition via the R3a algebra (defensive; a RateProblem's units compose by construction). answer_unit gives the answer's unit. No floats.
Ties to the gold: solves all 6 solved fixtures to gold; refuses both solver_refuses with non_integer_solution. Meaningful-fail: 100÷3 refuses (not 33), 99÷3=33. Off-serving. 5 tests.
generate/rate_comprehension/units.py: BaseUnit + RateUnit (numerator/denominator) + the three single-rate compositions — rate_times_time (mile/hour × hour = mile; refuses mile/hour × minute), rate_from_quantity_over_time (mile ÷ hour = mile/hour), time_from_quantity_over_rate (mile ÷ mile/hour = hour; refuses dollar ÷ mile/hour). A non-composing op raises UnitError (the wrong=0 dimensional gate), never fabricates a unit.
Deliberately tiny: bare-name units, no generic dimensional universe, no semantic unit-class typing, no unit conversion, no compound-of-compound. Fresh off-serving organ (generate/rate_comprehension/). 10 tests incl. all three refusals + consistent composition.
