What causes "No CDP session available for page" in mastra-ai/mastra?

Restart the screencast so a fresh CDP session is created for the current page

No CDP session available for page

Error message

No CDP session available for page

What it means

Same lazy CDP-session provider as the screencast path: after obtaining a page, the library looks up a CDP session via getCdpSessionForPage. If none exists — the page has no attached DevTools session — the provider throws. A CDP session is required to stream screencast frames.

Source

Thrown at browser/stagehand/src/stagehand-browser.ts:1031

  // Screencast (for Studio live view)
  // Uses Stagehand v3's native CDP access
  // ---------------------------------------------------------------------------

  override async startScreencast(options?: ScreencastOptions): Promise<ScreencastStream> {
    const threadId = options?.threadId;

    // Create a CDP session provider that gets a fresh session for the current page
    // On reconnect, this will get a fresh CDP session for whatever page is currently active
    const provider = {
      getCdpSession: async () => {
        const page = await this.threadManager.getPageForThread(threadId);
        if (!page) {
          throw new Error('No page available for screencast');
        }

        const session = this.getCdpSessionForPage(page);
        if (!session) {
          throw new Error('No CDP session available for page');
        }

        return session;
      },
      isBrowserRunning: () => this.isBrowserRunning(),
    };

    const stream = new ScreencastStreamImpl(provider, options);

    // Store the stream for potential future reconnection - keyed by thread
    const streamKey = this.getStreamKey(threadId);
    this.activeScreencastStreams.set(streamKey, stream);

    await stream.start();

    // Set up tab change detection
    await this.setupTabChangeDetection(threadId, stream);

View on GitHub (pinned to 75dd419e61)

Solutions

Restart the screencast so a fresh CDP session is created for the current page
Reconnect/relaunch the browser if sessions were detached by a reconnect
Ensure the page was opened through the library so it gets a CDP session
Verify getCdpSessionForPage coverage — check browser/CDP attach logs

Defensive patterns

Strategy: try-catch

Validate before calling

if (!browser.isBrowserRunning()) {
  await browser.reconnect(); // re-attach CDP sessions before screencasting
}

Try / catch

try {
  await browser.startScreencast({ threadId });
} catch (e) {
  if (e instanceof Error && e.message.startsWith('No CDP session')) {
    await browser.reconnect();
    await browser.startScreencast({ threadId });
  } else throw e;
}

Prevention

Restart screencasts after page navigations/target changes invalidate sessions
Open pages through the library API so CDP attach happens automatically
Reconnect the browser after network drops before resuming CDP-dependent features
Monitor for detached-session events if the library exposes them

When it happens

Trigger: getCdpSession invoked for a page that was never attached via CDP, or whose CDP session was detached (navigation to new target, browser reconnect, session cleanup).

Common situations: Screencast surviving a page navigation/target change that invalidated the old session; browser reconnect created a new page without reattaching; page opened outside the library's CDP attach path.

Related errors

AI-assisted analysis of mastra-ai/mastra@75dd419e61 (2026-08-30). Data as JSON: /api/errors/5b85c822ed0cb8c8. Report an issue: GitHub.