[fix]: dont attach to targets if already attached #1346

seanmcguire12 · 2025-12-04T01:04:41Z

why

this PR fixes the the intermittent “main world not ready for frame” error, which stemmed from us re‑attaching to targets that Chrome had already auto‑attached. Every extra Target.attachToTarget produces a new flattened session ID, so we ended up with two independent root CDP sessions for the same page.
when a cross-origin iframe (OOPIF) later tried to resolve its execution context, some code paths looked it up via the duplicate session, (the one that never saw Runtime.executionContextCreated)
this causedexecutionContexts.waitForMainWorld to time out even though the context already existed

what changed

inside the bootstrap() function (inside packages/core/lib/v3/understudy/context.ts), after grabbing existing targets via Target.getTargets, we now avoid directly calling Target.attachToTarget for any entry whose attached flag is already true
this means we keep exactly one session per target, which means that frame lookup uses the same session that actually observed its Runtime events

test plan

existing tests were catching this (most often shadow-iframe.spec.ts)
this test should no longer be flakey

Summary by cubic

Skip attaching to targets that are already attached to avoid duplicate attach calls when auto-attach has already run. This prevents redundant work and suppresses re-attach errors.

^{Written for commit 688f44f. Summary will update automatically on new commits.}

changeset-bot · 2025-12-04T01:04:44Z

🦋 Changeset detected

Latest commit: 688f44f

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@browserbasehq/stagehand	Patch
@browserbasehq/stagehand-evals	Patch

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greptile-apps · 2025-12-04T01:48:17Z

Greptile Overview

Greptile Summary

Fixed intermittent "main world not ready for frame" errors by preventing duplicate CDP session creation. Added check in bootstrap() to skip Target.attachToTarget for targets already attached via auto-attach, ensuring each target has exactly one session that receives all Runtime events.

Confidence Score: 5/5

This PR is safe to merge - it's a minimal, well-targeted fix
The change is a simple one-line guard that prevents a race condition without introducing new logic or side effects
No files require special attention

Important Files Changed

File Analysis

Filename	Score	Overview
packages/core/lib/v3/understudy/context.ts	5/5	Added guard to skip re-attaching already-attached targets, preventing duplicate CDP sessions
.changeset/fruity-clowns-pick.md	5/5	Changeset properly documents the fix as a patch release

Sequence Diagram

sequenceDiagram
    participant Chrome
    participant bootstrap
    participant conn as CdpConnection
    participant session as CDP Session
    
    Note over bootstrap: bootstrap() called
    bootstrap->>conn: enableAutoAttach()
    
    Note over Chrome,conn: Auto-attach occurs for some targets
    Chrome->>conn: Target.attachedToTarget (auto)
    conn->>session: Create session
    session->>session: Runtime.executionContextCreated
    
    bootstrap->>conn: getTargets()
    conn-->>bootstrap: List of targets (some with attached=true)
    
    loop For each target
        alt Target NOT already attached
            bootstrap->>conn: attachToTarget(targetId)
            conn->>session: Create new session
            Note over session: This session never sees<br/>Runtime events!
        else Target already attached (NEW)
            bootstrap->>bootstrap: Skip (continue)
            Note over bootstrap: Prevents duplicate session
        end
    end
    
    Note over session: OOPIF tries to resolve context
    session->>session: waitForMainWorld(frameId)
    alt With duplicate session (OLD)
        session-->>session: Timeout: "main world not ready"
    else Single session (NEW)
        session-->>session: Success: context found
    end

greptile-apps

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cubic-dev-ai

No issues found across 2 files

@miguelg719

This PR was opened by the [Changesets release](https://github.com/changesets/action) GitHub action. When you're ready to do a release, you can merge this and the packages will be published to npm automatically. If you're not ready to do a release yet, that's fine, whenever you add more changesets to main, this PR will be updated. # Releases ## @browserbasehq/[email protected] ### Patch Changes - [#1388](#1388) [`605ed6b`](605ed6b) Thanks [@miguelg719](https://github.com/miguelg719)! - Fix multiple click event dispatches on CDP and Anthropic CUA handling (double clicks) - [#1400](#1400) [`34e7e5b`](34e7e5b) Thanks [@seanmcguire12](https://github.com/seanmcguire12)! - don't write base64 encoded screenshots to disk when caching agent actions - [#1345](#1345) [`943d2d7`](943d2d7) Thanks [@tkattkat](https://github.com/tkattkat)! - Add support for aborting / stopping an agent run & continuing an agent run using messages from prior runs - [#1334](#1334) [`0e95cd2`](0e95cd2) Thanks [@tkattkat](https://github.com/tkattkat)! - Add support for google vertex provider - [#1410](#1410) [`d4237e4`](d4237e4) Thanks [@seanmcguire12](https://github.com/seanmcguire12)! - fix: include extract in stagehand.history() - [#1315](#1315) [`86975e7`](86975e7) Thanks [@tkattkat](https://github.com/tkattkat)! - Add streaming support to agent through stream:true in the agent config - [#1304](#1304) [`d5e119b`](d5e119b) Thanks [@miguelg719](https://github.com/miguelg719)! - Add support for Microsoft's Fara-7B - [#1346](#1346) [`4e051b2`](4e051b2) Thanks [@seanmcguire12](https://github.com/seanmcguire12)! - fix: don't attach to targets twice - [#1327](#1327) [`6b5a3c9`](6b5a3c9) Thanks [@miguelg719](https://github.com/miguelg719)! - Informed error parsing from api - [#1335](#1335) [`bb85ad9`](bb85ad9) Thanks [@seanmcguire12](https://github.com/seanmcguire12)! - add support for page.addInitScript() - [#1331](#1331) [`88d28cc`](88d28cc) Thanks [@seanmcguire12](https://github.com/seanmcguire12)! - fix: page.evaluate() now works with scripts injected via context.addInitScript() - [#1316](#1316) [`45bcef0`](45bcef0) Thanks [@tkattkat](https://github.com/tkattkat)! - Add support for callbacks in stagehand agent - [#1374](#1374) [`6aa9d45`](6aa9d45) Thanks [@miguelg719](https://github.com/miguelg719)! - Fix key action mapping in Anthropic CUA - [#1330](#1330) [`d382084`](d382084) Thanks [@seanmcguire12](https://github.com/seanmcguire12)! - fix: make act, extract, and observe respect user defined timeout param - [#1336](#1336) [`1df08cc`](1df08cc) Thanks [@tkattkat](https://github.com/tkattkat)! - Patch agent on api - [#1358](#1358) [`2b56600`](2b56600) Thanks [@tkattkat](https://github.com/tkattkat)! - Add support for 4.5 opus in cua agent ## @browserbasehq/[email protected] ### Patch Changes - [#1364](#1364) [`ca0630e`](ca0630e) Thanks [@tkattkat](https://github.com/tkattkat)! - Update model handling in agent evals cli - Updated dependencies \[[`605ed6b`](605ed6b), [`34e7e5b`](34e7e5b), [`943d2d7`](943d2d7), [`0e95cd2`](0e95cd2), [`d4237e4`](d4237e4), [`86975e7`](86975e7), [`d5e119b`](d5e119b), [`4e051b2`](4e051b2), [`6b5a3c9`](6b5a3c9), [`bb85ad9`](bb85ad9), [`88d28cc`](88d28cc), [`45bcef0`](45bcef0), [`6aa9d45`](6aa9d45), [`d382084`](d382084), [`1df08cc`](1df08cc), [`2b56600`](2b56600)]: - @browserbasehq/[email protected] ## @browserbasehq/[email protected] ### Patch Changes - Updated dependencies \[[`605ed6b`](605ed6b), [`34e7e5b`](34e7e5b), [`943d2d7`](943d2d7), [`0e95cd2`](0e95cd2), [`d4237e4`](d4237e4), [`86975e7`](86975e7), [`d5e119b`](d5e119b), [`4e051b2`](4e051b2), [`6b5a3c9`](6b5a3c9), [`bb85ad9`](bb85ad9), [`88d28cc`](88d28cc), [`45bcef0`](45bcef0), [`6aa9d45`](6aa9d45), [`d382084`](d382084), [`1df08cc`](1df08cc), [`2b56600`](2b56600)]: - @browserbasehq/[email protected] Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

@miguelg719

dont attach to targets if already attached

49252a0

changeset

688f44f

seanmcguire12 marked this pull request as ready for review December 4, 2025 01:45

greptile-apps bot reviewed Dec 4, 2025

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pirate approved these changes Dec 4, 2025

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seanmcguire12 merged commit 4e051b2 into main Dec 4, 2025
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github-actions bot mentioned this pull request Dec 4, 2025

Version Packages #1305

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miguelg719 pushed a commit that referenced this pull request Dec 4, 2025

[fix]: dont attach to targets if already attached (#1346)

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This was referenced Dec 5, 2025

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[fix]: dont attach to targets if already attached #1346

[fix]: dont attach to targets if already attached #1346

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seanmcguire12 commented Dec 4, 2025 •

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seanmcguire12 commented Dec 4, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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why

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test plan

Summary by cubic

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greptile-apps bot commented Dec 4, 2025

Greptile Overview

Greptile Summary

Confidence Score: 5/5

Important Files Changed

Sequence Diagram

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seanmcguire12 commented Dec 4, 2025 •

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