test: strengthen phase96 next_non_ws fixture

apps/tests/phase96_json_loader_next_non_ws_min.hako

@@ -2,15 +2,14 @@
 // Purpose: Trim系の実ループを fixtures/smoke で押さえる。
 
 static box Main {
-    main() {
-        // Input mirrors MiniJsonLoader.next_non_ws
-        local s = "hi"
+    next_non_ws(s) {
         local i = 0
         local n = s.length()
 
         loop(i < n) {
             local ch = s.substring(i, i + 1)
-            if ch == " " || ch == "\n" || ch == "\r" || ch == "\t" {
+            // Treat empty substring as whitespace for robustness
+            if ch == "" || ch == " " || ch == "\n" || ch == "\r" || ch == "\t" {
                 i = i + 1
             } else {
                 break
@@ -18,10 +17,15 @@ static box Main {
         }
 
         if i < n {
-            print(i)
-        } else {
-            print(-1)
+            return i
         }
+        return -1
+    }
+
+    main() {
+        // Input mirrors MiniJsonLoader.next_non_ws
+        print(next_non_ws(" " + " " + "hi")) // expect 2
+        print(next_non_ws(" " + "\t"))       // expect -1
         return "OK"
     }
 }