error highlighting and message improvements

backend/execution.py

@@ -45,6 +45,13 @@ def _is_link(value: Any) -> bool:
     )
 
 
+class NodeExecutionError(Exception):
+    """Wraps an error that occurred while executing a specific node."""
+    def __init__(self, node_id: str, original: Exception):
+        self.node_id = node_id
+        super().__init__(str(original))
+
+
 class ExecutionEngine:
     """Synchronous (blocking) graph executor. Run inside a thread pool from async code."""
 
@@ -99,12 +106,15 @@ class ExecutionEngine:
                 class_name = node_def["class_type"]
 
                 if class_name not in NODE_CLASS_MAPPINGS:
-                    raise ValueError(f"Unknown node type: '{class_name}'")
+                    raise NodeExecutionError(node_id, ValueError(f"Unknown node type: '{class_name}'"))
 
                 cls = NODE_CLASS_MAPPINGS[class_name]
                 raw_inputs = node_def.get("inputs", {})
                 input_types = cls.INPUT_TYPES()
-                inputs = self._resolve_inputs(raw_inputs, node_outputs, input_types)
+                try:
+                    inputs = self._resolve_inputs(raw_inputs, node_outputs, input_types)
+                except Exception as exc:
+                    raise NodeExecutionError(node_id, exc) from exc
                 input_signature = self._build_input_signature(class_name, raw_inputs, node_output_signatures)
 
                 cache_entry = self._get_cached_entry(node_id, class_name, input_signature)
@@ -118,8 +128,13 @@ class ExecutionEngine:
                     instance = cls()
                     func = getattr(instance, cls.FUNCTION)
                     start_time = perf_counter()
-                    with active_node(node_id):
+                    try:
-                        result = func(**inputs)
+                        with active_node(node_id):
+                            result = func(**inputs)
+                    except NodeExecutionError:
+                        raise
+                    except Exception as exc:
+                        raise NodeExecutionError(node_id, exc) from exc
                     elapsed_ms = (perf_counter() - start_time) * 1000.0
 
                 # Nodes must return a tuple; coerce single values just in case

backend/server.py

@@ -116,7 +116,7 @@ def create_app(
         from backend.plugin_loader import load_plugins
         load_plugins(plugins_dir())
 
-    from backend.execution import ExecutionEngine, new_prompt_id
+    from backend.execution import ExecutionEngine, NodeExecutionError, new_prompt_id
     from backend.node_registry import NODE_CLASS_MAPPINGS, get_all_node_info
 
     ensure_runtime_dirs(with_plugins=_plugins_on)
@@ -522,6 +522,12 @@ def create_app(
                     ),
                 )
                 broadcast(session_id, {"type": "execution_complete", "data": {"prompt_id": prompt_id}})
+            except NodeExecutionError as exc:
+                log.exception("Execution error on node %s", exc.node_id)
+                broadcast(session_id, {
+                    "type": "execution_error",
+                    "data": {"node_id": exc.node_id, "message": str(exc)},
+                })
             except Exception as exc:
                 log.exception("Execution error")
                 broadcast(session_id, {

frontend/src/App.jsx

@@ -1300,7 +1300,7 @@ function Flow() {
         case 'execution_start':
           setNodes((ns) => ns.map((n) => ({
             ...n,
-            data: { ...n.data, processingTimeMs: null },
+            data: { ...n.data, processingTimeMs: null, error: null },
           })));
           setExecutingNodeId(null);
           setStatus({ text: 'Running workflow…', level: 'info' });
@@ -1315,7 +1315,12 @@ function Flow() {
           break;
         case 'execution_error':
           setExecutingNodeId(null);
-          setStatus({ text: 'Error: ' + msg.data.message, level: 'error' });
+          if (msg.data.node_id) {
+            updateNodeData(msg.data.node_id, { error: msg.data.message });
+          }
+          if (!msg.data.node_id) {
+            setStatus({ text: 'Error: ' + msg.data.message, level: 'error' });
+          }
           console.error('[tono] execution error', msg.data);
           break;
         case 'preview':

frontend/src/CustomNode.jsx

@@ -1182,7 +1182,7 @@ function CustomNode({ id, data }) {
   return (
     <>
       {ctx?.executingNodeId === id && <div className="node-executing-glow" aria-hidden="true" />}
-    <div className="custom-node">
+    <div className={`custom-node${data.error ? ' node-error' : ''}`}>
       {/* Title */}
       <div className="node-title drag-handle" style={{ background: catColor }}>
         <div className="node-title-left">
@@ -1289,6 +1289,11 @@ function CustomNode({ id, data }) {
           <div className="node-warning">{data.warning}</div>
         )}
 
+        {/* Error notification */}
+        {data.error && (
+          <div className="node-error-message">{data.error}</div>
+        )}
+
         {scalarDisplay && !standaloneWidgets.some((w) => w.opts?.text_input) && (
           <div className="node-value-display">
             <div className="node-value-box">

frontend/src/styles.css

@@ -797,6 +797,21 @@ html, body, #root {
   border-bottom: 1px solid var(--warning-border);
 }
 
+.custom-node.node-error {
+  outline: 2px solid #ef4444;
+  outline-offset: -1px;
+  box-shadow: 0 0 8px rgba(239, 68, 68, 0.35);
+}
+
+.node-error-message {
+  padding: 3px 10px;
+  font-size: 10px;
+  color: #fca5a5;
+  background: rgba(239, 68, 68, 0.12);
+  border-top: 1px solid rgba(239, 68, 68, 0.3);
+  border-bottom: 1px solid rgba(239, 68, 68, 0.3);
+}
+
 .node-value-display {
   padding: 8px 10px 4px;
 }