Add optimality note: exhaustive enumeration confirms magnitude 3 is minimum

README.md

@@ -86,6 +86,10 @@ All have bias 0. Only the number of inputs changes.
 | Bias | 0 |
 | **Total** | **4 parameters** |
 
+## Optimality
+
+Exhaustive enumeration of all 129 weight configurations at magnitudes 0-3 confirms this circuit is **already at minimum magnitude (3)**. There is exactly one valid configuration at magnitude 3, and no valid configurations exist below it.
+
 ## Usage
 
 ```python