New back end half: host/chez/emit.janet consumes the host-neutral jolt IR
(ir.clj shapes) and emits Scheme, reusing the existing front-end (Option-2
backend swap). Covers the pure-functional subset: const/local/var/rt/if/do/let/
fn/invoke/def/loop/recur. Tested by hand-built IR run on Chez: (+ 1 2)=3,
fib(30)=832040, loop/recur sum=15 (4/4).
Finding: correct emit wraps every if-test in jolt-truthy?, costing ~3x on fib
(15.8ms vs hand-Scheme 5ms). Eliding the wrapper for known-boolean tests
recovers the ceiling (Phase-4 type-driven opt).
Remaining Phase 1: wire the live analyzer, var-cell late binding, RT module,
broader op coverage for mandelbrot.
874e3c7cf2