[teamleaderleo]

Leo (2026-11-03): "i think you guys are currently hiding it completely when there's only the one tab... but i think that's just too alien of a look"

#34327 made a pane's tab strip show at every tab count, so the pane always offers the row with its tabs shown. The code that existed only for a hidden lone tab (#33132, the page's solo layout in #33142, and the toolbar hole fill of #33261/#33407) no longer runs. This removes it; no behaviour changes.

Removed:

• PaneTabRowSharing.setTabRowTabs(shown:), tabRowHoleFill, the tabs: and toolbar: parameters of offerTabRow, and NSView.paintTabRowHole (with tabs always shown the fill was always nil, so the toolbar plate was never painted). The protocol default, PaneTabRowForwarding and the AgentPaneView conformance lose them too.
• AgentPaneTabRow.tabsShown, holeFill, soloTab in offered and the tabRow event, and nativeHoles(tabs:). The window-rim hole from Agent chat: the window's lit top rim runs unbroken over the header tools in the tab row #33346 stays.
• TabStripModel.holdsOneTab, TabStripView.laidOutOneTab, layOutPaneIfOneTabChanged.
• webviews: soloTab in header/tabRow.ts, the [data-solo-tab] CSS, VirtualTranscript and ThreadMinimap topInset, and header/underHeader.ts. Its record only decided whether the solo transcript could run up under the row; the lines it gated render on the same conditions as before Agent chat: a one-tab pane has no tab-row band; the chat runs up under the tab and its buttons #33142. The solo gallery variants and the one-tab case in thread-rail-foot-card.test.ts go too.
• Tests: AgentPaneTabRowSoloTests, TabStripHoldsOneTabTests, the tabsShown and hole-fill cases in AgentPaneTabRowHolesTests, chat-header-solo-tab.test.ts, under-header-lines.test.ts (its App.tsx string check was already stale on base), and theToolbarPaintsTheChatsHoleFill.

Test: theStripShowsAtOneHeightWhateverItsTabCount now checks what is on screen. At 0, 1 and 2 tabs, the strip and its + are shown inside the pane, there is one tab cell per tab, the centre of each tab and of + resolve to .strip, and a point past + resolves to .empty (the titlebar). The strip's frame stays the same across the counts.

Risk: low. This is a removal; only dead branches and their tests are deleted.

Agent session: agent session

🤖 Generated with Claude Code

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Summary by cubic

Removes the dead lone-tab solo row code. #34327 made a pane's tab strip show at every tab count, so the code that hid a lone tab and ran the transcript up under the row (#33132, #33142, #33261/#33407) no longer runs. Pure removal; no behavior change.

Removed

• Native: setTabRowTabs(shown:), the tabs:/toolbar: offer parameters, tabRowHoleFill and paintTabRowHole, holdsOneTab and layOutPaneIfOneTabChanged, and soloTab in the tabRow event. The window-rim hole stays.
• Web: the soloTab flag, [data-solo-tab] CSS, transcript and minimap topInset, and the underHeader gating record. The lines it gated still render on their own conditions.
• The dead tests for the above. theStripShowsAtOneHeightWhateverItsTabCount now asserts the strip, its +, and one tab cell per tab are on screen at 0, 1, and 2 tabs.

^{Written for commit c514479. Summary will update on new commits.}

[github-actions]

cmux status _{(one comment, edited in place; each line is updated by the job that owns it)}

Review c514479: HQ feed card · gallery before/after runs · checks

App of this head (app.zip, kept 1 day)

gh workflow run reload-build.yml -R manaflow-ai/cmux --ref feat-cmux-next -f tag=pr34392 -f ref=lane/lone-tab-dead-code -f platform=macos -f backend_mode=local

Gallery before/after for c514479: 16 states rendered, 0 images differ, 3418 more touched states not rendered. Images are in the run's artifact, not on this public PR; the independent review of this head reads them on its own, so the PR needs no hand-made screenshots of these states.

gh run download 41754453679 -R manaflow-ai/cmux -n gallery-advisory-34392-c5144795ccd35f1673449243124bccc31d67a81c (then read gallery-review.json)

States

State	Theme	Status	Diff	Picked by
agent-pane.chat-width/standard	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.chat-width/standard	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.chat-width/wide	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.chat-width/wide	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.chat-width/wide-blocks	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.chat-width/wide-blocks	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.composer-edge/short-edge	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.composer-edge/short-edge	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.composer-edge/wide-edge	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.composer-edge/wide-edge	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.composer-edge/no-edge	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.composer-edge/no-edge	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.composer-floats/scrolled-to-end	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.composer-floats/scrolled-to-end	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.composer-floats/composer-grown	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.composer-floats/composer-grown	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.composer-rest-gap/gap-40	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.composer-rest-gap/gap-40	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.composer-rest-gap/gap-56	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.composer-rest-gap/gap-56	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.composer-rest-gap/gap-72	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.composer-rest-gap/gap-72	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.continuation-spacing/shipped	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.continuation-spacing/shipped	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.continuation-spacing/two-thirds	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.continuation-spacing/two-thirds	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.continuation-spacing/half-tucked	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.continuation-spacing/half-tucked	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.continuation-spacing/before	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.continuation-spacing/before	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.copy-controls/output	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.copy-controls/output	Apple System Colors	unchanged	0%	own App.tsx

_{Pick other states with a Gallery: entry.id, entry.id/variant line in the PR body.}

Not verified: macOS jobs did not run: compile and app tests were skipped on c5144795cc; ci-status is green without them.

CI passes on c5144795cc (run 41754453841 attempt 1).
macOS jobs did not run: compile and app tests were skipped: Fast static checks skipped (the macos job needs both to succeed). Re-run CI once they pass, before merging.

Written by scripts/ci/classify_failures.py (ci-failure-attribution.yml); signatures are its SIGNATURES table. A machine verdict is the runner's fault, not this PR's; yours means the failing file is one this PR changes, also red on main that main's latest full suite fails the same way, seen on other PRs that it failed on another pull request's run lately.

web and size checks: green

Shipped in:

• cmux NEXT nightly 1.0.0-nightly.4177134165301 (4a7517355a)
• cmux NEXT nightly 1.0.0-nightly.4177399658201 (443d56f95d)
• cmux NEXT nightly 1.0.0-nightly.4177479261801 (0df62819ad)

[blacksmith-sh]

Found 43 test failures on Blacksmith runners:

Failures

Test	View Logs
/tmp/tmpgbqz8dfp/summary-fail.json (live):/summary-fail.json (live):	View Logs
/tmp/tmpjtvrw1qj/summary-missing.json (live):/summary-missing.json (live):	View Logs
[new_workspaces] debug.new_workspace timed 0 of 50 new workspace rows/ [new_workspaces] debug.new_workspace timed 0 of 50 new workspace rows	View Logs
[new_workspaces] the window draws no frames/[new_workspaces] the window draws no frames	View Logs
[tabs] debug.tab_switch timed 0 of 40 switches/ [tabs] debug.tab_switch timed 0 of 40 switches	View Logs
[tabs] the window draws no frames/[tabs] the window draws no frames	View Logs
main.DeveloperIdAppTests.test_download_prints_the_active_profile_only/ test_download_prints_the_active_profile_only	View Logs
convention violations found (ERROR lines above)./ convention violations found (ERROR lines above).	View Logs
stubs: /System/Library/Frameworks/Security.framework/Versions/A/Security has no stub/ Security has no stub	View Logs
stubs: CoreFoundation.tbd: install-name /System/Library/Frameworks/ CoreFoundation.framework/Versions/A/CoreFoundation, missing 1: ['_CFRetain']/ CoreFoundation, missing 1: ['_CFRetain']	View Logs

...and 33 more test failures. View all on Blacksmith

^{Need help on this PR? Tag @codesmith-bot with what you need.}

[teamleaderleo]

Review (subagent opus-5.5 medium): SHIP at 6a3664b

Checked that every removed symbol (setTabRowTabs, tabRowHoleFill, paintTabRowHole, holdsOneTab, laidOutOneTab, soloTab, data-solo-tab, topInset, underHeader) was dead after #34327 and is unreferenced. The App.tsx under-header lines render on the same conditions as before #33142. The rewritten strip test converts coordinates correctly. The earlier BLOCK at 5fe0d1b (a double blank line that would fail vp fmt) is fixed, as is a formatter line in thread-rail-foot-card.test.ts.

Follow-ups: none

[teamleaderleo]

Review (codex gpt-6.1-sol xhigh, router-review): SHIP at 6a3664b
Visual verdict: no images; Leo tries the build

No correctness regressions found in static review. Changed TS/TSX files parse. (router-review job 85a36fd557d63881647de033d7c933e0; its own --post hit the GraphQL quota, so the lane posted the receipt verbatim.)

Follow-ups:

• [P2] [follow-up] Visually verify the row at 0, 1 and 2 tabs (PaneContentView.swift:223).

[cursor]

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[teamleaderleo]

Awareness note from an agent lane that does not own this PR; it is not a review or a request to take the PR over.

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From the lone-tab toggle lane (ask-16ddd1693a). Leo at 2026-11-03T23:53Z, verbatim: "also we're restoring the top tab area right? we can put it back, just make it unobtrusive, it's a bit too funky with NO top bar at all plus the general shenanigans that are occuring... maybe you can leave it as an optional toggle feature for now that we can revisit later".

So the lone-tab hide (#33132) stays as an opt-in setting, off by default. #34392 deletes the plumbing it uses (setTabRowTabs, tabsShown/soloTab, tabRowHoleFill/paintTabRowHole, holdsOneTab/laidOutOneTab, the webview soloTab inset). Please do not land #34392: add a HOLD: line or close it with a comment. My PR (branch lane/lone-tab-hide-toggle) re-enables that code behind a setting.