Decode-Markdown-Test.md

Agent-Browser + Electron <webview> CDP Issue

Date: March 1, 2026
Project: Decode desktop app (Electron)
Context: Trying to automate embedded <webview> instances (example: Google home page) via agent-browser over CDP.

Summary

agent-browser can connect to an Electron CDP port (e.g. 9222) and control the top-level app window, but it cannot attach to a direct target endpoint like: ddd

• ws://localhost:9222/devtools/page/<webviewTargetId>

Even though Electron exposes cdeeadzdd webview target correctly at /json, agent-browser throws:

• No page found. Make sure the app has loaded content.

What Was Verified

1. Electron CDP target discovery is working.

• http://localhost:9222/json lists both:
  • type: "page" (Decode main window)
  • type: "webview" (Google)

2. The webview WebSocket endpoint itself is valid.

• Direct raw CDP calls to ws://localhost:9222/devtools/page/<webviewId> successfully returned:
  • document.title = "Google"
  • location.href = "https://www.google.com/"

3. agent-browser fails on that same target endpoint.

• Command reproduced:
  • agent-browser --cdp "ws://localhost:9222/devtools/page/<webviewId>" snapshot
• Result:
  • No page found. Make sure the app has loaded content.

Root Cause

agent-browser currently assumes CDP connections resolve to browser-level Playwright contexts/pages.

When given a target-level endpoint (/devtools/page/<id>), it still runs browser-context/page validation. That validation fails for this mode and exits early.

In short:

• Discovery endpoint is fine.
• Webview target endpoint is fine.
• agent-browser connection model does not support this endpoint type yet.

Code References (Where It Fails)

Installed agent-browser (0.7.6) checks contexts/pages after connectOverCDP:

• /Users/francoislaberge/.nvm/versions/node/v22.16.0/lib/node_modules/agent-browser/dist/browser.js#L796
• /Users/francoislaberge/.nvm/versions/node/v22.16.0/lib/node_modules/agent-browser/dist/browser.js#L804
• /Users/francoislaberge/.nvm/versions/node/v22.16.0/lib/node_modules/agent-browser/dist/browser.js#L809
• /Users/francoislaberge/.nvm/versions/node/v22.16.0/lib/node_modules/agent-browser/dist/browser.js#L811

Latest agent-browser (0.15.1) has same pattern:

• /Users/francoislaberge/conductor/workspaces/decode-next/berlin-v3/.context/tmp-agent-browser/package/dist/browser.js#L1277
• /Users/francoislaberge/conductor/workspaces/decode-next/berlin-v3/.context/tmp-agent-browser/package/dist/browser.js#L1292
• /Users/francoislaberge/conductor/workspaces/decode-next/berlin-v3/.context/tmp-agent-browser/package/dist/browser.js#L1294

Image Tests

Notes About Electron Skill Docs

The upstream Electron skill doc suggests webviews should be accessible via agent-browser tab, but it does not document a direct /devtools/page/<id> workflow or workaround.

Reference:

• https://github.com/vercel-labs/agent-browser/blob/main/skills/electron/SKILL.md

Practical Workarounds Right Now

1. Use agent-browser with browser-level endpoint (9222 or /devtools/browser/<id>) for main-window automation.
2. Use raw CDP (custom script/tooling) for direct webview-target automation (/devtools/page/<webviewId>).

Proposed Fix in Agent-Browser

To support webview target endpoints directly, agent-browser would need a dedicated target mode:

1. Detect .../devtools/page/<id> endpoints in connectViaCDP.
2. Skip browser contexts/pages validation in that mode.
3. Route commands (snapshot, click, type, fill, press, eval, screenshot) through raw CDP domains (Runtime, DOM, Input, Page) instead of Playwright Page APIs.

  graph TD;
      A-->B;
      A-->C;
      B-->D;
      C-->D;

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