Fix source indexing with modulo

recipes/woods-recipe-optimized.sexp

@@ -110,9 +110,10 @@
   ;; === OPTIMIZED PROCESS-PAIR MACRO ===
   ;; Uses fused-pipeline to batch rotate+hue+invert into single kernel
   (defmacro process-pair-fast (idx)
-    (let [;; Get sources for this pair
-          src-a (nth sources (* idx 2))
-          src-b (nth sources (+ (* idx 2) 1))
+    (let [;; Get sources for this pair (with safe modulo indexing)
+          num-sources (len sources)
+          src-a (nth sources (mod (* idx 2) num-sources))
+          src-b (nth sources (mod (+ (* idx 2) 1) num-sources))
           cfg (nth pair-configs idx)
           pstate (nth (bind pairs :states) idx)