fix: handle errors due to open dialogs during tool calls (#1953)

This change is part of the fix for #1069 
- Errors during tool calls are now consumed and handled as part of
McpResponse format

src/McpResponse.ts

@@ -203,6 +203,7 @@ export class McpResponse implements Response {
   #args: ParsedArguments;
   #page?: McpPage;
   #redactNetworkHeaders = true;
+  #error?: Error;
 
   constructor(args: ParsedArguments) {
     this.#args = args;
@@ -307,6 +308,10 @@ export class McpResponse implements Response {
     };
   }
 
+  setError(error: Error): void {
+    this.#error = error;
+  }
+
   attachNetworkRequest(
     reqId: number,
     options?: {requestFilePath?: string; responseFilePath?: string},
@@ -375,6 +380,10 @@ export class McpResponse implements Response {
     return this.#consoleDataOptions?.types;
   }
 
+  get error(): Error | undefined {
+    return this.#error;
+  }
+
   appendResponseLine(value: string): void {
     this.#textResponseLines.push(value);
   }
@@ -662,6 +671,7 @@ export class McpResponse implements Response {
       lighthouseResult: this.#attachedLighthouseResult,
       inPageTools,
       webmcpTools,
+      errorMessage: this.#error?.message,
     });
   }
 
@@ -680,6 +690,7 @@ export class McpResponse implements Response {
       lighthouseResult?: LighthouseData;
       inPageTools?: ToolGroup<ToolDefinition>;
       webmcpTools?: WebMCPTool[];
+      errorMessage?: string;
     },
   ): {content: Array<TextContent | ImageContent>; structuredContent: object} {
     const structuredContent: {
@@ -718,6 +729,7 @@ export class McpResponse implements Response {
       heapSnapshotNodes?: readonly object[];
       extensionServiceWorkers?: object[];
       extensionPages?: object[];
+      errorMessage?: string;
     } = {};
 
     const response = [];
@@ -1080,6 +1092,11 @@ Call ${handleDialog.name} to handle it before continuing.`);
       }
     }
 
+    if (data.errorMessage) {
+      response.push(`Error: ${data.errorMessage}`);
+      structuredContent.errorMessage = data.errorMessage;
+    }
+
     const text: TextContent = {
       type: 'text',
       text: response.join('\n'),

src/WaitForHelper.ts

@@ -128,8 +128,10 @@ export class WaitForHelper {
     action: () => Promise<unknown>,
     options?: {timeout?: number; handleDialog?: 'accept' | 'dismiss' | string},
   ): Promise<void> {
+    let dialogOpened = false;
     if (options?.handleDialog) {
       const dialogHandler = (dialog: Pick<Dialog, 'accept' | 'dismiss'>) => {
+        dialogOpened = true;
         if (options.handleDialog === 'dismiss') {
           void dialog.dismiss();
         } else if (options.handleDialog === 'accept') {
@@ -167,6 +169,10 @@ export class WaitForHelper {
     try {
       await navigationFinished;
 
+      if (dialogOpened) {
+        return;
+      }
+
       // Wait for stable dom after navigation so we execute in
       // the correct context
       await this.waitForStableDom();

src/index.ts

@@ -232,31 +232,35 @@ export async function createMcpServer(
             : new McpResponse(serverArgs);
 
           response.setRedactNetworkHeaders(serverArgs.redactNetworkHeaders);
-          if ('pageScoped' in tool && tool.pageScoped) {
-            const page =
-              serverArgs.experimentalPageIdRouting &&
-              params.pageId &&
-              !serverArgs.slim
-                ? context.getPageById(params.pageId)
-                : context.getSelectedMcpPage();
-            response.setPage(page);
-            await tool.handler(
-              {
-                params,
-                page,
-              },
-              response,
-              context,
-            );
-          } else {
-            await tool.handler(
-              // @ts-expect-error types do not match.
-              {
-                params,
-              },
-              response,
-              context,
-            );
+          try {
+            if ('pageScoped' in tool && tool.pageScoped) {
+              const page =
+                serverArgs.experimentalPageIdRouting &&
+                params.pageId &&
+                !serverArgs.slim
+                  ? context.getPageById(params.pageId)
+                  : context.getSelectedMcpPage();
+              response.setPage(page);
+              await tool.handler(
+                {
+                  params,
+                  page,
+                },
+                response,
+                context,
+              );
+            } else {
+              await tool.handler(
+                // @ts-expect-error types do not match.
+                {
+                  params,
+                },
+                response,
+                context,
+              );
+            }
+          } catch (err) {
+            response.setError(err);
           }
           const {content, structuredContent} = await response.handle(
             tool.name,
@@ -267,6 +271,9 @@ export async function createMcpServer(
           } = {
             content,
           };
+          if (response.error) {
+            result.isError = true;
+          }
           success = true;
           if (serverArgs.experimentalStructuredContent) {
             result.structuredContent = structuredContent as Record<

tests/index.test.js.snapshot

@@ -5,3 +5,7 @@ exports[`e2e > calls a tool 1`] = `
 exports[`e2e > calls a tool multiple times 1`] = `
 [{"type":"text","text":"## Pages\\n1: about:blank [selected]"}]
 `;
+
+exports[`e2e > returns blocked message when dialog is opened during tool execution 1`] = `
+{"content":[{"type":"text","text":"# Open dialog\\nalert: test dialog.\\nCall handle_dialog to handle it before continuing.\\nError: Failed to interact with the element with uid 1_1. The element did not become interactive within the configured timeout."}],"isError":true}
+`;

tests/index.test.ts

@@ -245,6 +245,37 @@ describe('e2e', () => {
       },
     );
   });
+
+  it('returns blocked message when dialog is opened during tool execution', async t => {
+    await withClient(async client => {
+      // Navigate to a page with a button that triggers a dialog on click
+      await client.callTool({
+        name: 'new_page',
+        arguments: {
+          url: `data:text/html,<button id="test" onclick="alert('test dialog')">Click me</button>`,
+        },
+      });
+
+      const snapshotResult = await client.callTool({
+        name: 'take_snapshot',
+        arguments: {},
+      });
+
+      const snapshotText = (snapshotResult.content as TextContent[])[0].text;
+      const match = snapshotText.match(/uid=(\d+_\d+)\s+button "Click me"/);
+      const uid = match ? match[1] : '1_1';
+
+      // Trigger the dialog
+      const result = await client.callTool({
+        name: 'click',
+        arguments: {
+          uid,
+        },
+      });
+
+      t.assert.snapshot?.(JSON.stringify(result));
+    });
+  });
 });
 
 async function getToolsWithFilteredCategories(