Codex VS Code extension unable to leverage in-app browser

What version of the IDE extension are you using?

26.5908.31748

What subscription do you have?

Copilot Business

Which IDE are you using?

VS Code 1.138.0-insider

What platform is your computer?

Microsoft Windows NT 10.0.26200.0 x64

What issue are you seeing?

All attempts made by Codex agent to load the built-in browser fail, preventing agent based testing of web code.

Codex will often try to validate code via the local browser, but eventually fail saying the in app browser is not exposed and fall back to asking the user to perform the tests.
I have prompted Codex with "Can you open the local IDE browser?" and receive:

`I’m using the in-app browser control skill to open the local IDE browser.

Called a tool
MCP tool call

node_repl.js

{
"title": "Connect to IDE browser",
"code": "if (globalThis.agent?.browsers == null) {\n const { setupBrowserRuntime } = await import("C:/Users/nnnnn/.codex/plugins/cache/openai-bundled/browser/26.715.72359/scripts/browser-client.mjs");\n await setupBrowserRuntime({ globals: globalThis });\n}\nif (globalThis.iab == null) {\n globalThis.iab = await agent.browsers.get("iab");\n nodeRepl.write(await iab.documentation());\n}"
}
Browser is not available: iab
The IDE browser connection didn’t appear on the first attempt, so I’m checking the built-in recovery path and retrying the connection.

Called 2 tools
MCP tool call

node_repl.js

{
"title": "Check browser connection",
"code": "nodeRepl.write(await agent.documentation.get("bootstrap-troubleshooting"));"
}

Browser Runtime Troubleshooting

• If browser setup completed but discovery or selection fails, reuse the existing agent; do not reset the JavaScript session or import another browser runtime.
• Inspect await agent.browsers.list() once to see which browser types are available. Do not assume that a missing requested browser can be replaced with another backend when the user explicitly named it.
• If a requested backend has specific troubleshooting documentation in the skill's setup catalog, read it before retrying.
• If the requested browser remains unavailable, report that plainly instead of controlling it through an unrelated browser tool or source-code workaround.
  MCP tool call

node_repl.js

{
"title": "Find IDE browser",
"code": "nodeRepl.write(await agent.browsers.list());"
}
[]
I can, but the local IDE browser isn’t currently available—the browser list is empty. Open or enable the IDE’s browser panel, then tell me when it’s ready and I’ll connect to it.

Well it seems to load fine via the native VS Code chat panel, calling "open_browser_page".

You’re right—that suggests there’s a direct IDE action available outside the browser-control binding I checked. I’ll look specifically for open_browser_page and use it if exposed here.

You’re correct: open_browser_page is likely a chat-host action, separate from the Browser plugin connection I tested. That action isn’t exposed in this agent session’s callable tools, so I can’t invoke it directly here—even though the IDE chat UI itself supports it.`

The VS Code version details:

Version: 1.138.0-insider (user setup)
Commit: 60ac69b364809ee6976d6dc3ed74cc7628f637da
Date: 2026-09-11T07:31:23Z
Electron: 42.10.0
ElectronBuildId: 15109253
Chromium: 148.0.7778.280
Node.js: 24.18.1
V8: 14.8.178.38-electron.0
@github/copilot: 1.0.84-4
@github/copilot-sdk: 1.0.13
OS: Windows_NT x64 10.0.26200

What steps can reproduce the bug?

Have the Codex agent write some html and then validate its work via the in-app browser.

What is the expected behavior?

The Codex agent invokes the local VS Code in-app browser to access and validate the developed code is as expected.

Additional information

I've been pointed towards other browser related bugs, but those seems to be for the Codex app, not the VS Code extension.

Reproduce with VS Code 1.138.0-insider and the reported Codex extension version by asking the agent to validate HTML in the in-app browser. Compare the unavailable agent.browsers.list() connection with the native open_browser_page action; done means the Codex agent can invoke the local VS Code browser and complete web-code validation.