Built-in browser does not render or navigate on v0.0.46 nightlies; desktop browser tools report "No desktop browser is connected to this session" #17010

What happened

I use the nightly channel. Since the Orchestrator V2 nightlies (the first was 20261003.2610), the built-in browser in the desktop app stopped working. Opening the Browser surface shows the tab and the local-servers list, but typing a URL and pressing Enter does nothing: the field clears back to "Search or enter URL" and no page ever loads, with no error anywhere in the UI. Agents in the thread cannot use the browser either — the desktop browser tools fail with [browser.disconnected] No desktop browser is connected to this session even though the desktop app is open on the thread. Restarting the app and rebooting the machine did not help. A screen recording shows the pane accepting google.com and then doing nothing.

Diagnosis

Agent-assisted investigation on the machine:

• Reproduced the agent-side failure live: browser.tabs.list and browser.tabs.open both fail with [browser.disconnected] No desktop browser is connected to this session. Open this session in the desktop app and wait for it to connect. while the desktop app is open on the thread. It persists across an app restart and a full reboot.
• Differential: server-hosted preview tabs still work. preview_open + preview_navigate to https://example.com succeeds and the tab reports the URL and title correctly (the tab was closed afterwards). So the server browser host is fine; the desktop browser host is the one that does not attach.
• No server-child*.log* files exist. Per the triage docs those are written only when a desktop backend crashes or fails to start, so the desktop backend is not crashing.
• server.trace.ndjson shows orchestration-v2.* startup spans; no browser-related error spans were found.
• The reporter first hit this after updating to the V2 nightlies; it worked before.

Steps to reproduce

1. Desktop app (Windows) connected to a T3 server on WSL2.
2. Open a thread, open the Browser surface ("Open a surface" → Browser).
3. Type google.com and press Enter. The field clears back to the placeholder; the pane stays on the "Local servers" list; nothing loads and no error is shown. Clicking a listed local server does nothing either.
4. In the same thread, have an agent call browser.tabs.list. It fails with [browser.disconnected] No desktop browser is connected to this session.
5. Quit and reopen the app, reboot the machine: unchanged.

Version

0.0.46-nightly.20261007.2787

Environment

Windows 11 host + WSL2 (kernel 6.18.33.2-microsoft-standard-WSL2); T3 server on the WSL side (linux x64); the desktop app connects to it. Environment label P7-DESKTOP.

Evidence

agent -> browser.tabs.list
[browser.disconnected] No desktop browser is connected to this session. Open this session
in the desktop app and wait for it to connect.

agent -> preview_open + preview_navigate https://example.com   (server-hosted tab)
available: true, url: https://example.com/, title: "Example Domain"

$ ls ~/.t3/userdata/logs/server-child*
none
$ grep -ic browser ~/.t3/userdata/logs/server.trace.ndjson
0

Screen recording of the dead pane: will be attached in a comment.

Related issues

• [Bug]: Browser address bar says "Search or enter URL" but cannot search, and search text fails silently #16639 (address bar cannot search; silent failure) and [Bug]: Environment-hosted browser tabs identify as HeadlessChrome with webdriver set, so sites like CNN and Google refuse to serve them #16638 (environment-hosted tabs blocked as HeadlessChrome) — a fix for this batch is in review: fix(server): environment-hosted browser tabs behave like a normal browser #16963.
• [Bug]: target=_blank links and window.open open a background tab in environment-hosted browser tabs #16640, [Bug]: A slow typed navigation blocks all input in an environment-hosted browser tab for 15 seconds #16641 — other environment-hosted tab bugs.
• fix(web): the desktop browser host answers every request that arrives together, not only the last #15965 (closed unmerged) documents the desktop host dropping batched requests and being disconnected by the broker; Built-in browser snapshots fail even after the desktop snapshot handler reports success #11223 (closed) is about desktop snapshots.
• None of these covers a desktop browser host that does not attach, with the pane silently doing nothing on the V2 nightlies.

Fix applied or workaround

None yet — investigation only; nothing was changed on the machine.

Filed by

opencode (deepseek-v4.1-flash) in a T3 Code agent session — agent-assisted triage; structure follows the via-triage template.