fix: regression after the #2443 (#2462)

This also includes a fix memory leak for the stashedElements.

src/McpPage.ts

@@ -471,6 +471,7 @@ export class McpPage implements ContextPage {
         if (!window.__dtmcp?.executeTool) {
           throw new Error('No tools found on the page');
         }
+
         const toolResult = await window.__dtmcp.executeTool(name, args);
 
         const stashDOMElement = (el: Element) => {
@@ -561,9 +562,15 @@ export class McpPage implements ContextPage {
       elementHandles.push(elementHandle);
     }
 
+    await this.pptrPage.evaluate(() => {
+      if (window.__dtmcp) {
+        window.__dtmcp.stashedElements = undefined;
+      }
+    });
+
     if (elementHandles.length) {
       using stack = new DisposableStack();
-      for (const handle of elementHandles) {
+      for (const handle of this.extraHandles) {
         stack.use(handle);
       }
       this.textSnapshot = await TextSnapshot.create(this, {

tests/tools/thirdPartyDeveloper.test.ts

@@ -886,5 +886,78 @@ describe('thirdPartyDeveloperTools', () => {
         {categoryExperimentalThirdParty: true},
       );
     });
+
+    it('disposes old handles when executing third party developer tools', async () => {
+      await withMcpContext(
+        async (response, context) => {
+          await setupThirdPartyDeveloperTools(response, context, () => {
+            const mockToolGroup = {
+              name: 'test-group',
+              description: 'test description',
+              tools: [
+                {
+                  name: 'test-tool',
+                  description: 'test tool description',
+                  inputSchema: {},
+                  execute: () => {
+                    const div = document.createElement('div');
+                    document.body.appendChild(div);
+                    return div;
+                  },
+                },
+              ],
+            };
+            window.addEventListener('devtoolstooldiscovery', (e: Event) => {
+              // @ts-expect-error Event has `respondWith`
+              e.respondWith(mockToolGroup);
+            });
+          });
+
+          const page = context.getSelectedMcpPage();
+          if (!page) {
+            assert.fail('No page found');
+          }
+
+          await executeThirdPartyDeveloperTool.handler(
+            {
+              params: {
+                toolName: 'test-tool',
+                params: JSON.stringify({}),
+              },
+              page,
+            },
+            response,
+            context,
+          );
+
+          const firstHandles = [...page.extraHandles];
+          assert.strictEqual(firstHandles.length, 1);
+          // @ts-expect-error Internal Puppeteer API
+          assert.ok(!firstHandles[0].disposed);
+
+          await executeThirdPartyDeveloperTool.handler(
+            {
+              params: {
+                toolName: 'test-tool',
+                params: JSON.stringify({}),
+              },
+              page,
+            },
+            response,
+            context,
+          );
+
+          const secondHandles = [...page.extraHandles];
+          assert.strictEqual(secondHandles.length, 1);
+          assert.notStrictEqual(firstHandles[0], secondHandles[0]);
+          // @ts-expect-error Internal Puppeteer API
+          assert.ok(!secondHandles[0].disposed);
+          // @ts-expect-error Internal Puppeteer API
+          assert.ok(firstHandles[0].disposed);
+        },
+        undefined,
+        {categoryExperimentalThirdParty: true},
+      );
+    });
   });
 });