bigdec values existed but +,-,*,/ and compare threw — the header even said
"arithmetic contagion is not modelled". Add the scale-aware engine on the
{unscaled, scale} pair (jbd-add/-sub/-mul/-div + comparison helpers) following
java.math.BigDecimal's rules: add/sub align to the larger scale, multiply adds
scales, divide gives the exact quotient at minimal scale or throws
ArithmeticException on a non-terminating expansion. Clojure contagion: a bigdec
mixed with an integer stays bigdec, a flonum operand wins (result is a double).
Wire it into the value-position shims only — jolt-add/-sub/-mul/-div (what
(reduce + bigs)/(apply * bigs) lower to) and compare — so the inlined native hot
path is untouched. A call-position (+ 1.5M 2.5M) still reaches the raw Chez op;
that needs the analyzer's :bigdec type (next).
Runtime .ss only, no re-mint. 13 JVM-certified corpus rows.
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