[juliusmarminge]

Since #22877, ServerBrowser.setUpTab marked a tab headless only when the desktop browser channel was available (!desktop && desktopChannel.available). In WSL-only mode the desktop starts its only backend without the browser fds, so the channel is unavailable and primary-environment server tabs stayed non-headless. rendersServerTabNatively then had Electron draw its own local page, which typed URLs never reached, while the server ran a separate headless page for agents. The fix drops the desktopChannel.available condition, so every tab the desktop does not draw (no channel, attach timeout, or adopted popup) is marked headless and the pane streams the server's page. When the channel is present and the desktop attaches, nothing changes. On servers with no desktop at all (plain t3, remote), tabs now carry headless: true. Nothing reads the flag outside the native-render check, which already needs an Electron primary environment, so there is no visible change there. I chose this over PR #31172, which reads the fd config in PreviewManager.open, because it keeps the decision in the one place that already makes it. The repro test 'a server started without the desktop browser channel marks its tabs headless' fails on the base ('expected undefined to be true') and passes with the fix. No new regex or parser. I did not re-run the desktop app on this branch; the repro step already reproduced the bug end to end there.

Fixes #17009

Reproduction on main

Commit origin/main f03db4f. WSL itself is not available on Linux, so I simulated WSL-only mode exactly at its root cause: I commented out desktopBrowserFd/desktopBrowserControlFd in the Linux primary backend config (apps/desktop/src/backend/DesktopBackendConfiguration.ts L518-519, local only, not committed) and ran the real desktop app (T3CODE_DEV_SEED=0 headless-desktop vp run dev:desktop), driving it over CDP. Steps: created a project, opened a thread, Open a surface -> Browser, typed example.com and pressed Enter. The address field cleared back to 'Search or enter URL', example.com appeared under 'Recently used', and no page loaded; clicking the listed local server localhost:7568 also did nothing. Control: I restored the two lines (Electron and the backend restarted with the fds) and ran the same steps: the tab loaded 'Example Domain' at https://example.com/. Failing test: apps/server/src/preview/ServerBrowser.test.ts, 'a server started without the desktop browser channel marks its tabs headless', runs ServerBrowser with the real DesktopBrowserChannel layer and no fds; on main the opened tab has headless undefined instead of true.

Evidence

Real Linux Electron desktop under Xvfb, with both desktop browser channel fds omitted to simulate the WSL-only backend condition. Fresh synthetic data, light theme, identical 484×780 Browser-pane crops. Steps: open Browser from a new-thread view, type example.com, press Enter; then click the listed localhost:7568 server from a new-tab pane.

Before	After
f03db4fbef	b51b3613d2
Before URL recording	After URL recording
Before local-server recording	After local-server recording

Capture driver · Seed script · Synthetic local page · Observations

AI-assisted; verified with the tests and tools listed above.

Not shown:

• Permanent blocker: native Windows with a WSL-only backend is unavailable on this Linux VM; evidence uses the explicitly supplied no-browser-channel simulation.
• Direct agent preview-tool operation and synchronization with a saved thread were not exercised; captures demonstrate desktop Browser navigation from the new-thread draft view. A direct MCP request using the desktop client credential was rejected with HTTP 401.

Tests

cd apps/server && vp test run src/preview/ServerBrowser.test.ts src/preview/Manager.test.ts: 79/79 passed. With the fix stashed, the repro test fails with 'expected undefined to be true'. vp run check:changed: format, lint, knip, typecheck (3 packages) and tests (2 files) all passed.

Not in this change

• Open PR fix(preview): typed URLs navigate browser tabs when WSL is the primary environment #31172 fixes the same bug a different way, by marking tabs headless in PreviewManager.open from the fd config; it could be closed in favour of this fix.
• When the desktop browser fds are missing, the WSL-only desktop backend still starts without a browser channel at all, so it streams the server's page instead of rendering natively. Giving WSL backends a real channel is a separate feature.

AI-assisted; verified with the tests and tools listed above.

[macroscopeapp]

Approvability

Verdict: Approved at b51b361

Macroscope's review found this PR approvable — Server-backed browser tabs are now marked headless even when no desktop browser channel exists, allowing the preview pane to render the page actually being controlled. Desktop-connected tabs remain unchanged, and the change is limited to rendering selection.

^{You can add or adjust custom eligibility rules. Learn more.}

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	5.0 KiB	5.0 KiB	0 B (0.0%)	6.8 KiB	✅
Codex	Thread snapshot wire	3.8 KiB	3.8 KiB	0 B (0.0%)	4.9 KiB	✅
Codex	Live turn WebSocket wire	1.2 KiB	1.2 KiB	0 B (0.0%)	2.0 KiB	✅
Codex	Live turn WebSocket decoded	21.5 KiB	21.5 KiB	0 B (0.0%)	24.4 KiB	✅
Codex	Live turn messages	1	1	0 (0.0%)	8	✅
Claude	Total thread wire	5.0 KiB	5.0 KiB	0 B (0.0%)	6.8 KiB	✅
Claude	Thread snapshot wire	3.8 KiB	3.8 KiB	0 B (0.0%)	4.9 KiB	✅
Claude	Live turn WebSocket wire	1.2 KiB	1.2 KiB	0 B (0.0%)	2.0 KiB	✅
Claude	Live turn WebSocket decoded	21.9 KiB	21.9 KiB	0 B (0.0%)	24.4 KiB	✅
Claude	Live turn messages	1	1	0 (0.0%)	8	✅

Other scenarios

All 64 scenario measurements match main.

All 64 scenario measurements

Provider	Scenario	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	short turn resume	WebSocket decoded	10.5 KiB	10.5 KiB	0 B (0.0%)	12.7 KiB	✅
Codex	short turn resume	WebSocket messages	2	2	0 (0.0%)	2	✅
Codex	long turn running, cold open	HTTP decoded	281.7 KiB	281.7 KiB	0 B (0.0%)	302.7 KiB	✅
Codex	long turn running, cold open	rows	75	75	0 (0.0%)	75	✅
Codex	long turn running, history page	HTTP decoded	92.4 KiB	92.4 KiB	0 B (0.0%)	107.4 KiB	✅
Codex	long turn running, history page	rows	75	75	0 (0.0%)	75	✅
Codex	long turn finished, cold open	HTTP decoded	381.5 KiB	381.5 KiB	0 B (0.0%)	410.2 KiB	✅
Codex	long turn finished, cold open	rows	151	151	0 (0.0%)	151	✅
Codex	long turn finished, socket cold open	WebSocket decoded	381.6 KiB	381.6 KiB	0 B (0.0%)	410.2 KiB	✅
Codex	long turn finished, socket cold open	WebSocket messages	2	2	0 (0.0%)	2	✅
Codex	long turn finished, socket cold open	rows	151	151	0 (0.0%)	151	✅
Codex	long turn finished, work page	HTTP decoded	186.2 KiB	186.2 KiB	0 B (0.0%)	200.2 KiB	✅
Codex	long turn finished, work page	rows	150	150	0 (0.0%)	150	✅
Codex	idle thread resume	WebSocket decoded	65 B	65 B	0 B (0.0%)	200 B	✅
Codex	idle thread resume	WebSocket messages	1	1	0 (0.0%)	1	✅
Codex	fleet shell snapshot	HTTP decoded	41.6 KiB	41.6 KiB	0 B (0.0%)	53.7 KiB	✅
Codex	fleet shell snapshot	rows	27	27	0 (0.0%)	27	✅
Codex	fleet shell subscribe	WebSocket decoded	65 B	65 B	0 B (0.0%)	200 B	✅
Codex	fleet shell subscribe	WebSocket messages	1	1	0 (0.0%)	1	✅
Codex	fleet shell resume check	HTTP decoded	18 B	18 B	0 B (0.0%)	100 B	✅
Codex	fleet shell resume check	rows	0	0	0	0	✅
Codex	stale shell reload	HTTP decoded	41.6 KiB	41.6 KiB	0 B (0.0%)	53.7 KiB	✅
Codex	stale shell reload	rows	27	27	0 (0.0%)	27	✅
Codex	stale shell resume	WebSocket decoded	140 B	140 B	0 B (0.0%)	400 B	✅
Codex	stale shell resume	WebSocket messages	2	2	0 (0.0%)	2	✅
Codex	stale todo list cold open	HTTP decoded	72.4 KiB	72.4 KiB	0 B (0.0%)	83.0 KiB	✅
Codex	stale todo list cold open	rows	75	75	0 (0.0%)	75	✅
Codex	stale todo list cold open	nodes	2	2	0 (0.0%)	4	✅
Codex	stale todo list cold open	subagents	2	2	0 (0.0%)	4	✅
Codex	stale todo list cold open	plans	1	1	0 (0.0%)	2	✅
Codex	stale todo list cold open	providerTurns	1	1	0 (0.0%)	2	✅
Codex	stale todo list cold open	checkpoints	1	1	0 (0.0%)	2	✅
Claude	short turn resume	WebSocket decoded	10.6 KiB	10.6 KiB	0 B (0.0%)	12.7 KiB	✅
Claude	short turn resume	WebSocket messages	2	2	0 (0.0%)	2	✅
Claude	long turn running, cold open	HTTP decoded	283.3 KiB	283.3 KiB	0 B (0.0%)	302.7 KiB	✅
Claude	long turn running, cold open	rows	75	75	0 (0.0%)	75	✅
Claude	long turn running, history page	HTTP decoded	93.4 KiB	93.4 KiB	0 B (0.0%)	107.4 KiB	✅
Claude	long turn running, history page	rows	75	75	0 (0.0%)	75	✅
Claude	long turn finished, cold open	HTTP decoded	384.2 KiB	384.2 KiB	0 B (0.0%)	410.2 KiB	✅
Claude	long turn finished, cold open	rows	151	151	0 (0.0%)	151	✅
Claude	long turn finished, socket cold open	WebSocket decoded	384.3 KiB	384.3 KiB	0 B (0.0%)	410.2 KiB	✅
Claude	long turn finished, socket cold open	WebSocket messages	2	2	0 (0.0%)	2	✅
Claude	long turn finished, socket cold open	rows	151	151	0 (0.0%)	151	✅
Claude	long turn finished, work page	HTTP decoded	188.1 KiB	188.1 KiB	0 B (0.0%)	200.2 KiB	✅
Claude	long turn finished, work page	rows	150	150	0 (0.0%)	150	✅
Claude	idle thread resume	WebSocket decoded	66 B	66 B	0 B (0.0%)	200 B	✅
Claude	idle thread resume	WebSocket messages	1	1	0 (0.0%)	1	✅
Claude	fleet shell snapshot	HTTP decoded	42.2 KiB	42.2 KiB	0 B (0.0%)	53.7 KiB	✅
Claude	fleet shell snapshot	rows	27	27	0 (0.0%)	27	✅
Claude	fleet shell subscribe	WebSocket decoded	66 B	66 B	0 B (0.0%)	200 B	✅
Claude	fleet shell subscribe	WebSocket messages	1	1	0 (0.0%)	1	✅
Claude	fleet shell resume check	HTTP decoded	18 B	18 B	0 B (0.0%)	100 B	✅
Claude	fleet shell resume check	rows	0	0	0	0	✅
Claude	stale shell reload	HTTP decoded	42.2 KiB	42.2 KiB	0 B (0.0%)	53.7 KiB	✅
Claude	stale shell reload	rows	27	27	0 (0.0%)	27	✅
Claude	stale shell resume	WebSocket decoded	140 B	140 B	0 B (0.0%)	400 B	✅
Claude	stale shell resume	WebSocket messages	2	2	0 (0.0%)	2	✅
Claude	stale todo list cold open	HTTP decoded	73.4 KiB	73.4 KiB	0 B (0.0%)	83.0 KiB	✅
Claude	stale todo list cold open	rows	75	75	0 (0.0%)	75	✅
Claude	stale todo list cold open	nodes	2	2	0 (0.0%)	4	✅
Claude	stale todo list cold open	subagents	2	2	0 (0.0%)	4	✅
Claude	stale todo list cold open	plans	1	1	0 (0.0%)	2	✅
Claude	stale todo list cold open	providerTurns	1	1	0 (0.0%)	2	✅
Claude	stale todo list cold open	checkpoints	1	1	0 (0.0%)	2	✅

Baseline: a2685e6 · PR result: b51b361 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 108.5 KiB
• Claude decoded thread snapshot: 108.8 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.

[coderabbitai]

No actionable comments were generated in the recent review.

Walkthrough

ServerBrowser now marks a tab headless whenever no desktop page is connected, regardless of desktop-channel availability. A regression test covers the unavailable-channel case.

Changes: Server tab headless fallback

Layer / File(s)	Summary
Headless fallback and regression test apps/server/src/preview/ServerBrowser.ts, apps/server/src/preview/ServerBrowser.test.ts	The headless fallback now applies whenever no desktop page is connected. A test checks that a tab is marked headless when the desktop channel is unavailable.

Estimated code review effort: 2 (Simple) | ~5 minutes

Change: Bug fix · Severity of issue fixed: Medium

Possibly related issues

• Issue #32940 reports that the panel remains on the new-tab page in WSL-only mode. This change covers headless marking when no desktop page is connected, but the issue’s exact cause is not verified.

Possibly related PRs

• pingdotgg/t3code#27043: Changes the same headless condition in ServerBrowser.ts and tests the no-desktop-channel case.
• pingdotgg/t3code#31172: Addresses headless marking for server tabs when the desktop browser channel is absent, through PreviewManager.open.
• pingdotgg/t3code#28488: Applies the same headless condition in ServerBrowser.createTab and tests the no-desktop-channel case.

Suggested labels: bugfix

Suggested reviewers: t3dotgg, macroscopeapp, maria-rcks

Merge Risk: Minimal · up to b51b3

Tabs that the desktop does not draw now fall back to the server's page, which fixes the reported navigation failure when no desktop browser channel exists. No concrete merge-blocking risk remains.

Pre-merge checks: 3 · 1

Failed checks: 1 inconclusive

Check name	Status	Explanation	Resolution
Linked Issues check		Issue #17009 reports two symptoms: (1) the built-in browser pane accepts a URL but does not navigate, and (2) agent desktop browser tools fail with [browser.disconnected]. The diff changes one conditi…	Provide evidence that agent desktop browser tools (browser.tabs.list, browser.tabs.open) no longer fail with [browser.disconnected] when the desktop has no browser channel. This can be a test or a run in the desktop app on this head. Altern…

Passed checks: 3 passed

Check name	Status	Explanation
Title check		The title names the main change: the browser pane navigates when the desktop backend has no browser channel. The PR removes the desktopChannel.available condition so that tabs the desktop does not dra…
Out of Scope Changes check		The source change is a one-condition change in ServerBrowser.ts setUpTab. It directly implements the requirement that unrendered tabs stream the server page. The test change in ServerBrowser.test.ts i…
Description check		The description follows the repository template closely. It has a clear Problem section, a Change section that explains why dropping the desktopChannel.available condition fixes the bug, and a Scope s…

Full details: Title check

Explanation

The title names the main change: the browser pane navigates when the desktop backend has no browser channel. The PR removes the desktopChannel.available condition so that tabs the desktop does not draw are marked headless and stream the server's page. The title is specific and follows a conventional commit format.

Full details: Out of Scope Changes check

Explanation

The source change is a one-condition change in ServerBrowser.ts setUpTab. It directly implements the requirement that unrendered tabs stream the server page. The test change in ServerBrowser.test.ts is a regression test for the same condition. The PR description says the flag is read only by the native-render check, and this was not contradicted in the reviewed diff. No unrelated changes appear in the whole-PR diff from f03db4f to b51b361. The PR does not add WSL browser-channel support, which the PR description excludes as a separate feature.

Full details: Description check

Explanation

The description follows the repository template closely. It has a clear Problem section, a Change section that explains why dropping the desktopChannel.available condition fixes the bug, and a Scope section that links issue #17009 and explains the bug fix. Its Verification section lists a failing-then-passing repro test, a 79/79 test run, check:changed results, and before/after evidence with a reproduction on main. The author also states items not checked, including native Windows with a WSL-only backend and the agent preview tool path. The template's optional agent-model line is not present, but that is minor. The description is mostly complete, so the check passes.

Full details: Linked Issues check

Explanation

Issue #17009 reports two symptoms: (1) the built-in browser pane accepts a URL but does not navigate, and (2) agent desktop browser tools fail with [browser.disconnected]. The diff changes one condition in apps/server/src/preview/ServerBrowser.ts (setUpTab, around L887-891). The condition was !desktop && desktopChannel.available. It is now !desktop. Tabs that the desktop does not draw are marked headless, so the pane streams the server page. This addresses symptom (1) on the code path. The added test 'a server started without the desktop browser channel marks its tabs headless' covers the same path. The diff does not touch the code that emits the [browser.disconnected] error, and no change in this PR is shown to connect agent desktop browser tools to the session. The PR author reports a failing test on the base and a passing test with the fix. The author did not re-run the desktop app on this branch, so end-to-end navigation on this head is reported, not verified here.

Resolution

Provide evidence that agent desktop browser tools (browser.tabs.list, browser.tabs.open) no longer fail with [browser.disconnected] when the desktop has no browser channel. This can be a test or a run in the desktop app on this head. Alternatively, state that the tool path is out of scope for this PR and the issue should stay open for it. Also provide the end-to-end run on this head that the PR's Evidence section plans to capture.

Finishing Touches

Generate unit tests (beta)

• Commit to this branch
• Create a new PR

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Recent review info

Run configuration

• Source mode: Auto
• Repository: pingdotgg/t3code
• Branch: factory/issue-17009-a28601
• File: .coderabbit.config.ts
• Commit: b51b361
• Layers: Repository TS config
• Review profile: CHILL
• Plan: Team
• Run ID: d5a4fc0d-9e6f-44a9-b249-7f5fb8a32c91

Commits

Reviewing files that changed from the base of the PR and between a2685e6 and b51b361.

Files selected for processing: 2

• apps/server/src/preview/ServerBrowser.test.ts
• apps/server/src/preview/ServerBrowser.ts

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