🐛 fix deterministic case-insensitive Route.URL key selection

Agent-Logs-Url: https://github.com/gofiber/fiber/sessions/6b2ae8da-f708-42b5-9e9b-7e3795de0ec5

Co-authored-by: gaby <835733+gaby@users.noreply.github.com>

Author: Copilot

router.go

@@ -127,14 +127,16 @@ func buildRouteURL(route *Route, params Map) (string, error) {
 		if val, found = params[segment.ParamName]; !found && !route.caseSensitive {
 			// Fall back to a case-insensitive match using a deterministic winner
 			var matchedKey string
+			foundMatch := false
 			for key := range params {
-				if utils.EqualFold(key, segment.ParamName) && (!found || key < matchedKey) {
+				if utils.EqualFold(key, segment.ParamName) && (!foundMatch || key < matchedKey) {
 					matchedKey = key
-					found = true
+					foundMatch = true
 				}
 			}
-			if found {
+			if foundMatch {
 				val = params[matchedKey]
+				found = true
 			}
 		}
 

router_test.go

@@ -2449,6 +2449,14 @@ func Test_Route_URL(t *testing.T) {
 		require.NoError(t, err)
 		require.Equal(t, "/user/fiber", url)
 
+		// When multiple keys case-fold to the same param name and no exact key
+		// exists, the lexicographically-smallest key wins deterministically.
+		for range 50 {
+			url, err = route.URL(Map{"nAme": "second", "Name": "first"})
+			require.NoError(t, err)
+			require.Equal(t, "/user/first", url)
+		}
+
 		// When multiple keys case-fold to the same param name, prefer the exact match.
 		url, err = route.URL(Map{"name": "exact", "Name": "fallback"})
 		require.NoError(t, err)