diff --git a/src/browser/utils/messages/StreamingMessageAggregator.ts b/src/browser/utils/messages/StreamingMessageAggregator.ts
index 4e0c8f9ec1..68768fb55f 100644
--- a/src/browser/utils/messages/StreamingMessageAggregator.ts
+++ b/src/browser/utils/messages/StreamingMessageAggregator.ts
@@ -54,12 +54,16 @@ function hasSuccessResult(result: unknown): boolean {
 }
 
 /**
- * Check if a tool result indicates failure (for tools that return { success: boolean })
+ * Check if a tool result indicates failure.
+ * Handles both explicit failure ({ success: false }) and implicit failure ({ error: "..." })
  */
 function hasFailureResult(result: unknown): boolean {
-  return (
-    typeof result === "object" && result !== null && "success" in result && result.success === false
-  );
+  if (typeof result !== "object" || result === null) return false;
+  // Explicit failure
+  if ("success" in result && result.success === false) return true;
+  // Implicit failure - error field present
+  if ("error" in result && result.error) return true;
+  return false;
 }
 
 export class StreamingMessageAggregator {
diff --git a/src/node/services/streamManager.ts b/src/node/services/streamManager.ts
index fb22c84b1c..815d8d0210 100644
--- a/src/node/services/streamManager.ts
+++ b/src/node/services/streamManager.ts
@@ -938,6 +938,7 @@ export class StreamManager extends EventEmitter {
 
             // Format error output
             const errorOutput = {
+              success: false,
               error:
                 typeof toolErrorPart.error === "string"
                   ? toolErrorPart.error