lua: Lua 5.0-style arg auto-binding in vararg functions; assert-counter diagnostic +2 tests

lib/lua/runtime.sx

@@ -1591,3 +1591,21 @@
 
 ;; T — debug/testC placeholder for tests that check it conditionally
 (define T nil)
+
+;; Build Lua 5.0-style `arg` table: array + .n counter, skipping leading explicit params.
+(define
+  lua-varargs-arg-table
+  (fn (args skip)
+    (let ((t {}) (n 0))
+      (begin
+        (define
+          va-build
+          (fn (i)
+            (when (< i (len args))
+              (begin
+                (set! n (+ n 1))
+                (dict-set! t (str n) (nth args i))
+                (va-build (+ i 1))))))
+        (va-build skip)
+        (dict-set! t "n" n)
+        t))))