diff --git a/internal/mcp/tools/spark_submit.go b/internal/mcp/tools/spark_submit.go
index 3c79078..33c83d7 100644
--- a/internal/mcp/tools/spark_submit.go
+++ b/internal/mcp/tools/spark_submit.go
@@ -80,26 +80,29 @@ func (d *Deps) SparkSubmitHandler(ctx context.Context, req mcp.CallToolRequest)
 		return errResult("spark_submit: " + err.Error()), nil
 	}
 
-	// Reject paths that didn't come through upload_file on this server.
-	// Cluster-local paths and arbitrary host paths are unreachable from the MCP
-	// server's spark-submit, so we fail fast with a clear message rather than
-	// letting spark-submit produce a confusing FileNotFoundException later.
-	if d.UploadStore != nil {
-		if _, err := d.UploadStore.Validate(scriptPath); err != nil {
-			return errResult(fmt.Errorf("spark_submit: script_path %q is not from upload_file on this server; upload the file first via upload_file and pass back the path field: %w", scriptPath, err).Error()), nil
-		}
+	executorMemory, err := req.RequireString("executor_memory")
+	if err != nil {
+		return errResult("spark_submit: " + err.Error()), nil
 	}
 	queue, err := req.RequireString("queue")
 	if err != nil {
 		return errResult("spark_submit: " + err.Error()), nil
 	}
-	executorMemory, err := req.RequireString("executor_memory")
-	if err != nil {
-		return errResult("spark_submit: " + err.Error()), nil
-	}
 
 	args := req.GetArguments()
 
+	// Reject paths that didn't come through upload_file on this server.
+	// Cluster-local paths and arbitrary host paths are unreachable from the MCP
+	// server's spark-submit, so we fail fast with a clear message rather than
+	// letting spark-submit produce a confusing FileNotFoundException later.
+	// Placed after all required-string parses so error messages surface in
+	// field order (cluster_id, master, ..., script_path, queue, ...).
+	if d.UploadStore != nil {
+		if _, err := d.UploadStore.Validate(scriptPath); err != nil {
+			return errResult(fmt.Sprintf("spark_submit: script_path %q is not from upload_file on this server; upload the file first via upload_file and pass back the path field", scriptPath)), nil
+		}
+	}
+
 	// deploy_mode is required for forward compatibility but the builder does not
 	// emit --deploy-mode, matching the Python reference's actual behavior. If the
 	// Go side needs --deploy-mode later, add it here and document the divergence.