Windows 26.1007.21434: browser-control subagent sees no browsers while IAB pages render and Chrome setup shows Manage #53306

Environment

• Windows desktop app, version 26.1007.21434, build 13901, production distribution.
• The app's update check returned up_to_date.
• Browser, unified-computer-use, and computer-use plugins are enabled in local configuration.
• Chrome Computer Use setup shows "Manage", as confirmed by the user.

Problem

The user-visible browser and the agent's browser-control connection disagree. The built-in browser opens and renders pages; app screen context shows multiple browser tabs. However, the delegated browser-control agent cannot discover or connect to either Chrome or the built-in browser.

Observed results

• cua.getState(): {"apps":[],"browsers":[]}.
• cua.listBrowsers(): [].
• cua.listTabs({browser:"chrome"}): Browser is not available: chrome.
• Creating a Chrome tab through cua.createBrowserTab("chrome", ...) produces the same error before site access.
• Connecting to an existing built-in-browser tab by URL produces Browser is not available: iab.
• An earlier initial child-agent turn could discover the built-in-browser backend. Requesting a visible IAB tab in that child returned IAB visibility is not supported in a subagent thread. Later continuations returned no browsers. The relationship between that visibility limitation and the connection failure is unknown.

Reproduction

1. Use the Windows desktop app and complete Chrome connection setup until Computer Use shows "Manage".
2. Open website tabs in the built-in browser; the user can view the pages.
3. Request read-only browser inspection and delegate it to a browser-control subagent.
4. Run the documented browser discovery and tab access methods.
5. Observe empty browser discovery or "Browser is not available" before any page content can be read.

The user reports the same overall problem after a full PC restart, trying a different chat, and explicitly selecting Chrome. In the reproduced child-agent session, resetting the JavaScript interaction session also did not restore discovery. The user reports browser operation previously worked.

Expected behavior

When the browser is connected and pages are visible, an authorized browser-control agent should receive an available connection or a specific actionable reason for its unavailability. If subagent continuation is unsupported or requires a separate route, this should be clearly reported.

Impact

The assistant cannot read or operate signed-in websites, blocking a requested storefront listing workflow. Public web search and user-facing browser display continue to work.

Related reports

• Windows Codex 26.924.2738.0: built-in @Browser “saved browser permissions could not be verified”; Chrome “Browser is not available: chrome” after update #49247
• Chrome plugin works in UI, but Codex browser bridge reports Browser is not available: chrome. #37307
• Existing subagent loses IAB after normal completion: modern continuation does not recapture its route #51105

These reports describe similar symptoms; no shared root cause is asserted. This report contains no credentials, personal data, storefront identity, page content, session transcripts, or raw logs.