Chez inc 3k: converter + string-op RT shims

str/subs/vec/keyword/symbol/compare/int/double/gensym — host-coupled seed natives
the overlay assumes, now def-var!'d into clojure.core via host/chez/converters.ss
(loaded last, str reuses jolt-pr-str). Semantics match the seed: str-render-one
for str (nil->"", bare chars, regex source), the 3-way core-compare port, int
truncates. The symbol no-ns sentinel is #f to match emit's quoted-symbol lowering
(jolt-symbol #f "x"), so (= 'x (symbol "x")) holds — jolt= compares ns with strict
equal?, and jolt-nil vs #f would otherwise diverge.

Prelude parity 1220 -> 1326/2497, 0 new divergences. Floor raised to 1326; three
newly-reached *ns*/var-rendering cases added to the allowlist (Phase 2). run-prelude
and the per-case program file are now PID-unique so concurrent chez runs don't read
each other's half-written files.

test/chez/run-corpus-prelude.janet

@@ -50,6 +50,9 @@
    "source order with a nil value (phm form)" true
    "close on throw" true
    "ns-name of *ns*" true
+   "str of *ns*" true
+   "*ns* user" true
+   "str of a var" true
    "*clojure-version* major" true
    "*unchecked-math*" true})
 
@@ -126,8 +129,9 @@
 # Regression floor (inc 3j baseline): raise as runtime gaps close, like the probe
 # reach-floor and the suite baseline. The gate fails if parity drops below it, or
 # on any NEW (un-allowlisted) divergence — a real Chez correctness regression.
-# Full-corpus baseline at inc 3j: 1220/2497. Strided runs scale the floor down.
-(def base-floor (scan-number (or (os/getenv "JOLT_CHEZ_PRELUDE_FLOOR") "1220")))
+# Full-corpus baseline: inc 3j 1220/2497; inc 3k (converters) 1326. Strided runs
+# scale the floor down.
+(def base-floor (scan-number (or (os/getenv "JOLT_CHEZ_PRELUDE_FLOOR") "1326")))
 (def floor (if (os/getenv "JOLT_CORPUS_LIMIT") 0 base-floor))
 (when (or (> (length diverged) 0) (< pass floor))
   (printf "REGRESSION: pass %d < floor %d or %d new divergence(s)" pass floor (length diverged)))