fix: set statusCode property on error in layer.js to ensure proper error handling

lib/layer.js

@@ -226,7 +226,7 @@ function decodeParam (val) {
   } catch (err) {
     if (err instanceof URIError) {
       err.message = 'Failed to decode param \'' + val + '\''
-      err.status = 400
+      err.status = err.statusCode = 400
     }
 
     throw err

test/layer.js

@@ -0,0 +1,42 @@
+'use strict'
+const { it, describe } = require('mocha')
+const assert = require('assert')
+const Layer = require('../lib/layer')
+
+describe('decodeParam', function () {
+  it('should set statusCode to 400 on URIError', function () {
+    const layer = new Layer('/:param', {}, function handle () {})
+
+    // Create a malformed URI component that will cause a decoding error
+    const malformedParam = '%Z'
+
+    try {
+      // Using match will internally call decodeParam with our malformed value
+      layer.match('/' + malformedParam)
+
+      // If we reach here, no error was thrown, which is a failure
+      assert.fail('Expected URIError to be thrown')
+    } catch (err) {
+      // Verify that the URIError was enhanced with the correct status properties
+      assert.strictEqual(err.status, 400, 'Expected err.status to be 400')
+      assert.strictEqual(err.statusCode, 400, 'Expected err.statusCode to be 400')
+      assert.strictEqual(err.message, `Failed to decode param '${malformedParam}'`, 'Expected proper error message')
+    }
+  })
+
+  it('should successfully decode valid parameters', function () {
+    // Create a layer with a parameter route - note the need to provide a handler function
+    const layer = new Layer('/:param', {}, function handle () {})
+
+    // Create a valid encoded parameter
+    const original = 'test value'
+    const encoded = encodeURIComponent(original)
+
+    // Match will internally call decodeParam with our encoded value
+    const matched = layer.match('/' + encoded)
+
+    // Verify the parameter was properly decoded
+    assert.strictEqual(matched, true, 'Route should match')
+    assert.strictEqual(layer.params.param, original, 'Parameter should be properly decoded')
+  })
+})