Add optimality note: exhaustive enumeration confirms magnitude 7 is minimum

README.md

@@ -56,6 +56,10 @@ The select signal routes the data to exactly one output.
 
 Single-layer circuit - both outputs are linearly separable.
 
+## Optimality
+
+Exhaustive enumeration of all 19,825 weight configurations at magnitudes 0-7 confirms this circuit is **already at minimum magnitude (7)**. There is exactly one valid configuration at magnitude 7, and no valid configurations exist below it.
+
 ## Usage
 
 ```python