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.
0c: persistent HAMT on Chez is ~41x faster than Janet's HAMT on the collections
map-churn (258.6 -> 6.3 ms), ~15x off mutable-native (inherent persistence cost).
Decision: self-host the persistent collections in Clojure; substrate is not the
bottleneck. See docs/chez-phase0-results.md.
0a hardening: NUL-separated keyword intern key (no ns/name collision), non-finite
-safe jolt-hash. 37/37.
0a (host/chez/values.ss): Jolt value model on Chez — nil sentinel distinct from
#f/'(), interned keywords, ns+meta symbols, exactness-aware = and consistent
hash. Chez numeric tower gives ratios/bignums free. 33/33 tests.
0b (test/chez/): extract test/spec/*.janet defspec tables into corpus.edn (2655
cases, valid as both EDN and Janet data), and a runner that drives ANY jolt
binary via the CLI boundary with per-case subprocess isolation. Pluggable target
(JOLT_BIN) so the same corpus gates every host. Baseline vs Janet build/jolt:
2641/2655, 14 known CLI divergences allowlisted; gate fails only on NEW ones.
