[BUG] @mastra/agent-browser: Browser fails to initialize with thread scope (default)

[chaoticsmol]

Bug Description

When using @mastra/agent-browser with the default scope: 'thread' configuration, the browser fails to initialize. The launch() method completes successfully but getPage() throws "Browser not launched. Call launch first."

Environment

• @mastra/agent-browser: v0.1.0
• agent-browser: v0.19.0
• Node.js: $(node --version 2>/dev/null || echo "unknown")
• Platform: macOS (Darwin)
• Chrome installed: Yes

Steps to Reproduce

import { AgentBrowser } from '@mastra/agent-browser';

const browser = new AgentBrowser({ headless: false }); // scope defaults to 'thread'
await browser.launch();
const page = await browser.getPage(); // throws: "Browser not launched. Call launch first."

Root Cause Analysis

In @mastra/agent-browser, the doLaunch() method (lines 561-580) has this logic:

async doLaunch() {
  const scope = this.threadManager.getScope();
  if (scope === "thread") {
    this.sharedManager = new BrowserManager();
    this.threadManager.setSharedManager(this.sharedManager);
    return; // Returns early WITHOUT launching the browser!
  }
  // shared scope continues to launch...
  await this.sharedManager.launch(launchOptions);
}

For thread scope, the browser is supposed to launch lazily when a thread session is created via createSession(). However, in AgentBrowserThreadManager.createSession():

if (this.scope === "thread") {
  // ...
  if (threadId !== DEFAULT_THREAD_ID && !existingSession) {
    await this.getManagerForThread(threadId);  // Only creates if threadId !== DEFAULT_THREAD_ID
  }
}

The lazy launch only triggers when threadId !== DEFAULT_THREAD_ID. When using the default thread ID, no browser is ever launched.

Workaround

Use scope: 'shared' instead:

const browser = new AgentBrowser({ 
  headless: false,
  scope: 'shared'
});

Expected Behavior

Browser should initialize properly with the default thread scope configuration, or the documentation should clearly state that thread scope requires explicit thread ID management.

Impact

• All users relying on default configuration are affected
• Breaking change for anyone migrating to this package
• No clear error message indicating the configuration issue

[daneatmastra]

Thank you for reporting this issue! We have labeled it for trio-tb and we will look into it as soon as possible.

If you're experiencing an error, please provide a minimal reproducible example whenever possible to help us resolve it quickly.

[Aayush-engineer]

Found the root cause in two places — opening a PR.

[intojhanurag]

Found the root cause in two places — opening a PR.

closing my PR in respect of your PR .