Log error on failed xpath lookup

.changeset/many-guests-collect.md

@@ -0,0 +1,5 @@
+---
+"@browserbasehq/stagehand": patch
+---
+
+Add level 0 logging when xpath lookup fails in act and observe handlers

packages/core/lib/v3/handlers/actHandler.ts

@@ -468,6 +468,14 @@ function normalizeActInferenceElement(
   const xp = xpathMap[elementId as EncodedId];
   const trimmed = trimTrailingTextNode(xp);
   if (!trimmed) {
+    v3Logger({
+      category: "action",
+      message: `LLM returned ID ${elementId}, there is no xpath keyed by this ID`,
+      level: 0,
+      auxiliary: {
+        elementId: { value: elementId, type: "string" },
+      },
+    });
     return undefined;
   }
 

packages/core/lib/v3/handlers/observeHandler.ts

@@ -147,7 +147,17 @@ export class ObserveHandler {
             const lookUpIndex = elementId as EncodedId;
             const xpath = combinedXpathMap[lookUpIndex];
             const trimmedXpath = trimTrailingTextNode(xpath);
-            if (!trimmedXpath) return undefined;
+            if (!trimmedXpath) {
+              v3Logger({
+                category: "observation",
+                message: `LLM returned ID ${elementId}, there is no xpath keyed by this ID`,
+                level: 0,
+                auxiliary: {
+                  elementId: { value: elementId, type: "string" },
+                },
+              });
+              return undefined;
+            }
 
             // For dragAndDrop, convert element ID in arguments to xpath (target element)
             let resolvedArgs = rest.arguments;