uniquify duplicate fn params (macro _ _ expanders)

Chez rejects duplicate lambda formals, so any (fn [_ _] ...) failed to compile
— including every macro expander, whose &form/&env slots both expand to _. The
analyzer now renames each earlier duplicate param to a fresh name (Clojure binds
the last occurrence, so the earlier ones are shadowed and unreferenceable). SCI
load 162 -> 186/218.

host/chez/run-sci.ss

@@ -1,11 +1,11 @@
 ;; run-sci.ss — SCI conformance: load borkdude/sci's own source (vendor/sci) through
 ;; joltc and require its forms to compile+eval. A real-world Clojure-compatibility
 ;; stress test. Pure Chez, no Janet. Floor-gated like the corpus: a regression below
-;; the floor (or the count today, 160/218) fails. Raise the floor as host gaps close
+;; the floor (or the count today, 186/218) fails. Raise the floor as host gaps close
 ;; (the tail is genuine gaps — set! on vars, some macro/def shapes).
 ;;
 ;;   chez --script host/chez/run-sci.ss
-;;   JOLT_SCI_FLOOR=N    override the floor (default 160)
+;;   JOLT_SCI_FLOOR=N    override the floor (default 186)
 ;;   SCI_VERBOSE=1       print each failing form's error
 (import (chezscheme))
 
@@ -74,7 +74,7 @@
   load-order)
 
 (printf "\nSCI load: ~a/~a forms ok (~a fail)\n" total-ok (+ total-ok total-fail) total-fail)
-(define floor (let ((s (getenv "JOLT_SCI_FLOOR"))) (if s (string->number s) 160)))
+(define floor (let ((s (getenv "JOLT_SCI_FLOOR"))) (if s (string->number s) 186)))
 (when (< total-ok floor)
   (printf "REGRESSION: ~a forms loaded < floor ~a\n" total-ok floor))
 (flush-output-port)

jolt-core/jolt/analyzer.clj

@@ -114,9 +114,25 @@
                    (if ph (conj phints [nm ph]) phints)))))
       {:fixed fixed :rest rest-name :hints hints :phints phints})))
 
+;; Clojure lets a later param shadow an earlier same-named one (a macro expander
+;; uses _ for both its &form and &env slots, so its param list is (_ _ …)); the
+;; body binds the LAST occurrence. Chez rejects duplicate formals, so rename every
+;; earlier duplicate to a fresh name — it is shadowed and unreferenceable.
+(defn- uniquify-params [names]
+  (let [n (count names)]
+    (loop [i 0 out []]
+      (if (< i n)
+        (let [nm (nth names i)
+              dup? (loop [j (inc i)]
+                     (cond (>= j n) false
+                           (= nm (nth names j)) true
+                           :else (recur (inc j))))]
+          (recur (inc i) (conj out (if dup? (gen-name (str nm "_")) nm))))
+        out))))
+
 (defn- analyze-arity [ctx pvec body env fn-name]
   (let [pp (parse-params ctx (vec (form-vec-items pvec)))
-        fixed (:fixed pp)
+        fixed (uniquify-params (:fixed pp))
         rst (:rest pp)
         ;; Always a recur target, variadic included: the back end gives the rest
         ;; param an ordinary positional slot (holding the collected seq), so recur