Chez Phase 1 (increment 2): live analyzer -> Chez, var cells, RT, mandelbrot

Wire the real pipeline end to end: host/chez/driver.janet boots a compile-mode
jolt ctx, runs the EXISTING Janet-hosted analyzer on actual Clojure source to
real IR, feeds it to the Scheme emitter, and runs the result on Chez. Analysis
stays on Janet (the analyzer ports to Chez in Phase 2); execution is on Chez.

emit.janet now consumes live IR (pv/phm-normalized like the Janet backend) and
covers what the analyzer actually emits, not the hand-built inc-1 shapes:
- core ops arrive as :var clojure.core/+ etc., not :rt — lowered to native
  Scheme via a native-ops table (mirrors backend.janet's), `=` to jolt=.
- var cells (host/chez/rt.ss): :def -> def-var!, :var -> var-deref. Late binding
  so cross-var calls (run -> count-point) and the entry crossing resolve at use.
- named fns (defn / fn self-name) bind via letrec so self-recursion resolves.
- unsupported stdlib/host refs (no core on Chez yet) are rejected at EMIT time
  (clean out-of-subset signal) instead of deref'ing to nil and failing at runtime.

Number model: jolt is all-doubles (no ratios; (/ 1 2) is 0.5), so literals emit
as flonums — matches the Janet host and keeps Chez out of exploding exact
rationals (mandelbrot). jolt-num->string prints integer-valued without ".0".

Two real bugs found via the corpus probe and fixed (regression rows added):
- loop bound in parallel (Scheme named-let) but Clojure loop is sequential — a
  later init must see earlier bindings; wrap a let* around the loop.
- #(...) shorthand gensyms params with a trailing `#`, invalid in Scheme — munge
  it to `_`.

Gate: test/chez/emit-test.janet runs the real analyzer -> Chez for (+ 1 2),
fib(30)=832040, mandelbrot run(40), and the two regressions, parity-checked
against the Janet oracle (6/6). First parity number via the new subset probe
(test/chez/run-corpus-chez.janet, JOLT_CHEZ_CORPUS=1): 182/182 compiled corpus
cases pass, 0 divergences; 2473/2655 out of subset pending core on Chez. Full
jpm/run-tests gate green (125 files). Chez tests skip cleanly without `chez`.

Perf note (unchanged plan): emitted fib(30) ~23ms vs hand-Scheme ~5ms — the
jolt-truthy? wrapper (~3x) plus flonum (not fixnum) arithmetic, both Phase-4
type-specialization levers.

test/chez/README.md

@@ -36,3 +36,21 @@ gate's job is to catch *regressions* the port introduces, not to bless these.
 The runner tests through `jolt -e`, exactly how the Chez host will be exercised —
 not the in-process `eval-string` the Janet `defspec` harness uses. The two differ
 on a handful of cases (the allowlist), and the CLI boundary is the portable one.
+
+## Phase 1 — first parity number (subset probe)
+The full `run-corpus.janet` gate drives an `-e`-capable jolt binary; the Chez
+host can't answer arbitrary `-e` until all of clojure.core is bootstrapped onto
+Chez (Phase 2). Until then, `run-corpus-chez.janet` reports parity for the subset
+the Phase-1 back end (`host/chez/emit.janet`) can already compile: each case is
+run through the live analyzer → Scheme emitter → Chez via `host/chez/driver`.
+Cases that reference unimplemented stdlib/host fns fail to EMIT (a clean
+compile-time signal) and are counted "out of subset", not as divergences.
+
+    JOLT_CHEZ_CORPUS=1 janet test/chez/run-corpus-chez.janet
+
+Baseline (2026-06-17): **182/182 compiled cases pass, 0 divergences**; 2473/2655
+out of subset (await core on Chez). It's a slow report (a Chez subprocess per
+case), so it's gated behind `JOLT_CHEZ_CORPUS` out of the default suite, like the
+benches. `test/chez/emit-test.janet` is the fast Phase-1 unit gate (real
+analyzer → Chez parity for fib/mandelbrot + regressions); both skip cleanly when
+`chez` isn't on PATH.