added error thrown on act from a not-supported observe result (#520)

* added error thrown on act from a not-supported observe result

* added todo for validation

Author: miguelg719

Diff for: .changeset/selfish-panthers-guess.md

@@ -0,0 +1,5 @@
+---
+"@browserbasehq/stagehand": patch
+---
+
+Performing act from a 'not-supported' ObserveResult will now throw an informed error

Diff for: lib/handlers/actHandler.ts

@@ -86,6 +86,29 @@ export class StagehandActHandler {
     });
 
     const method = observe.method;
+    if (method === "not-supported") {
+      this.logger({
+        category: "action",
+        message: "Cannot execute ObserveResult with unsupported method",
+        level: 1,
+        auxiliary: {
+          error: {
+            value:
+              "NotSupportedError: The method requested in this ObserveResult is not supported by Stagehand.",
+            type: "string",
+          },
+          trace: {
+            value: `Cannot execute act from ObserveResult with unsupported method: ${method}`,
+            type: "string",
+          },
+        },
+      });
+      return {
+        success: false,
+        message: `Unable to perform action: The method '${method}' is not supported in ObserveResult. Please use a supported Playwright locator method.`,
+        action: observe.description || `ObserveResult action (${method})`,
+      };
+    }
     const args = observe.arguments ?? [];
     // remove the xpath prefix on the selector
     const selector = observe.selector.replace("xpath=", "");
@@ -168,6 +191,7 @@ export class StagehandActHandler {
    * This method will observe the page and then perform the act on the first element returned.
    */
   public async observeAct(instruction: string): Promise<ActResult> {
+    // TODO: Add validation for the supported playwright methods
     const observeResults = await this.stagehandPage.observe(
       `Find the most relevant element to perform an action on given the following action: ${instruction}. 
       Provide an action for this element such as ${Object.values(SupportedPlaywrightAction).join(", ")}, or any other playwright locator method. Remember that to users, buttons and links look the same in most cases.