fix(operator): interpolate desc.url so failure message shows the URL

common/workflow-operator/src/main/scala/org/apache/texera/amber/operator/source/fetcher/URLFetcherOpExec.scala

@@ -32,11 +32,9 @@ class URLFetcherOpExec(descString: String) extends SourceOperatorExecutor {
   override def produceTuple(): Iterator[TupleLike] = {
 
     val urlObj = new URL(desc.url)
-    val input = getInputStreamFromURL(urlObj)
-    val contentInputStream = input match {
-      case Some(value) => value
-      case None        => IOUtils.toInputStream(s"Fetch failed for URL: $desc.url", "UTF-8")
-    }
+    val contentInputStream = getInputStreamFromURL(urlObj).getOrElse(
+      IOUtils.toInputStream(s"Fetch failed for URL: ${desc.url}", "UTF-8")
+    )
     Iterator(if (desc.decodingMethod == DecodingMethod.UTF_8) {
       TupleLike(IOUtils.toString(contentInputStream, "UTF-8"))
     } else {

common/workflow-operator/src/test/scala/org/apache/texera/amber/operator/source/fetcher/URLFetcherOpExecSpec.scala

@@ -44,4 +44,27 @@ class URLFetcherOpExecSpec extends AnyFlatSpec with BeforeAndAfter {
     assert(!iterator.hasNext)
   }
 
+  // On a failed fetch the fallback message must interpolate `desc.url` itself,
+  // not the descriptor's reflectionToString dump. A file:// URL to a nonexistent
+  // path makes getInputStreamFromURL return None deterministically and offline,
+  // so the failure branch is exercised without depending on external connectivity.
+  it should "report only the URL, not the operator descriptor, when the fetch fails" in {
+    val missingUrl =
+      java.nio.file.Files
+        .createTempDirectory("texera-urlfetcher-regression-")
+        .resolve("missing")
+        .toUri
+        .toString
+    opDesc.url = missingUrl
+    opDesc.decodingMethod = DecodingMethod.UTF_8
+    val fetcherOpExec = new URLFetcherOpExec(objectMapper.writeValueAsString(opDesc))
+    val content = fetcherOpExec.produceTuple().next().getFields.toList.head.asInstanceOf[String]
+
+    assert(content == s"Fetch failed for URL: ${opDesc.url}")
+    // Guard against the pre-fix `$desc.url` behavior, which leaked the whole
+    // descriptor dump (class name + internal fields) into the message.
+    assert(!content.contains("URLFetcherOpDesc"))
+    assert(!content.contains("operatorId"))
+  }
+
 }