small fixes

components/explorers/rounding-explorer.tsx

@@ -3,6 +3,7 @@
 import { useState, useCallback } from "react";
 import { Card } from "@/components/ui/card";
 import { StepControls } from "./step-controls";
+import { parseStrictDecimal } from "@/lib/math/validation";
 
 type RoundTarget = "whole" | "1dp" | "2dp" | "1sf" | "2sf" | "3sf";
 
@@ -384,9 +385,9 @@ export function RoundingExplorer() {
   function handleGo() {
     setError("");
     const trimmed = input.trim();
-    const val = parseFloat(trimmed);
-    if (isNaN(val)) {
-      setError("Enter a valid number.");
+    const val = parseStrictDecimal(trimmed);
+    if (val === null) {
+      setError("Enter a valid number (digits and decimal point only).");
       return;
     }
     if (val < 0) {