[teamleaderleo]

Leo (2026-11-03, on the nightly): "latest nightly still not fixed yet?", then "i mean the rectangle near the buttons".

Fixes #33261.

What changes

A chat alone in its pane paints its own surface (appearance.surfaces.agentPane) across the whole tab row (header.css, .acpmux-shell[data-tab-row][data-solo-tab], from #33142). In Chromium the chat is a window above the pane that cuts a hole for the pane's toolbar (AgentPaneTabRow.nativeHoles). That hole showed the pane's own shade, so a block of another colour sat beside the chat's tools.

The chat now gives the pane the colour its page paints there:

• PaneTabRowSharing.tabRowHoleFill returns it, worked out by AgentPaneTabRow.holeFill.
• offerTabRow fills the toolbar with it after each offer.

The fill is a plate that starts below the window's lit top rim (PaneTabRowRim.height, 1 pt). #33346 leaves that rim uncovered across the chat's tools, and the plate keeps it unbroken over the toolbar too.

There is no fill with tabs shown, because the page leaves the row clear then. There is none on WebKit either, because the page sits under the toolbar and already paints there. A clear page colour (glass) gives no fill, and leaving the row or switching to non-chat content clears it. A theme change lays the pane out again, which offers the row again and reads the colour anew. Nothing changes behind the tools themselves, and the toggled Session Info plate is untouched.

Scope

This covers the one-tab Chromium case that #33261 describes. In a pane with two or more tabs the page is clear across the whole row (#32944), so nothing paints behind the tools that differs from the strip, and this PR leaves that path alone.

Relation to the nightly report

Leo's capture shows the window's top rim breaking into a flat line where the header tools begin. #33346, which landed while this was in flight, fixes that: the page now leaves the rim uncovered over the tools. This PR fixes the other rectangle in that row, the toolbar block in a lone Chromium chat that has its own colour (#33261), and keeps #33346's rim intact over the toolbar.

Tests

• AgentPaneTabRowHolesTests.aLoneChromiumChatsToolbarHolePaintsThePagesSurface checks the fill matrix: lone tab in Chromium, tabs shown, WebKit, out of the row, and a clear page.
• AgentPaneTabRowHolesTests.aLoneWebKitChatPaintsNoToolbarHole checks that a shared page host on WebKit gets no fill.
• AgentPaneTabRowHolesTests.aLoneChromiumChatHandsThePaneItsSurfaceForTheToolbar checks that the chat's fill follows its own theme scope and that the fill is dropped when the row ends.
• TabRowToolsStayClickableTests.theToolbarPaintsTheChatsHoleFill checks that the pane's toolbar takes the fill below the 1 pt rim, keeps its own background clear, and goes clear again.

Design spec: design/chat-header.md (the row reads as one surface behind the tools).

Agent session: agent session

🤖 Generated with Claude Code

[teamleaderleo]

Review (codex gpt-6.1-sol xhigh, router-review): BLOCK at 2ebf589

BLOCK at 2ebf589
Visual verdict: no images; Leo tries the build

1. [P1] [blocking] AgentPaneTabRowHolesTests.swift:106: AgentPaneView gains its PaneTabRowSharing conformance in CmuxNextApp, which this test target neither imports nor depends on. These view.tabRowHoleFill accesses therefore do not compile. Assert view.model.tabRow.holeFill here, or test the conformance in the app target.

2. [P1] [blocking] TabRowToolsStayClickableTests.swift:161: The fixture never assigns pane.toolbar. PaneContentView leaves it nil, so this new test always fails at #require. Install a PaneToolbar before settling the layout.

3. [P1] [blocking] AgentPaneTabRow.swift:77: view.page != nil identifies the shared host, which also supports WebKit. With WebKit selected and a translucent chat surface override, the page already paints beneath the toolbar; this additional fill darkens that rectangle, regressing the existing WebKit appearance. Gate on the actual Chromium engine and cover shared-host WebKit in the integration test.

Swift/AppKit checks could not run here because the box has no Swift toolchain.

Follow-ups:

4. [P2] [follow-up] PaneContentView.swift:229: Verify the toolbar visually in Leo’s build; no after screenshots were supplied.

[teamleaderleo]

Review (codex gpt-6-astra high, router-review): BLOCK at cb22a60

BLOCK at cb22a60
Visual verdict: no images; Leo tries the build

1. [P1] [blocking] Packages/macOS/CmuxNext/Sources/CmuxNextAgentPane/AgentPaneTabRow.swift:77 — The // comment swallows shares: shares, tabsShown: row.tabsShown,. The call therefore omits two required arguments and prevents compilation. Move the comment above the call and restore both arguments.
2. [P2] [follow-up] review/images/README.txt:2 — No after screenshots are available. Verify the toolbar fill visually in the build.

[teamleaderleo]

Review (codex, router-review): SHIP at 8a2f84f

Reviewer: codex gpt-6-astra high, fast tier.

Follow-ups: 1. Each lands as an issue in this repo that links this receipt; the lane that opened the PR fixes it forward.

SHIP at 8a2f84f
Visual verdict: no images; Leo tries the build

No correctness regressions found in the layout, theme, or fill-clearing paths. AppKit tests could not run in this Linux box.

1. [P2] [follow-up] Packages/macOS/CmuxNext/Sources/CmuxNextApp/PaneContentView.swift:229: No after screenshots were supplied; verify the toolbar colour and theme switching in the macOS build.

Follow-ups:

• Verify the toolbar visually on macOS (finding 1).

[cmux-bot]

cmux-bot approves 8a2f84f: an independent review passed this exact head (router-review receipt by teamleaderleo). A push needs a new review; a later BLOCK at this head dismisses this approval.

[github-actions]

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

Review 4b243b6: 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=pr33407 -f ref=lane/ux-header-rect -f platform=macos -f backend_mode=local

red: cmux-next checks (god files, concurrency, crash safety, l10n); NEW: red check: Script tests (pin-cmux-tui, embed-cef, ensure-cef store) (+1 more) is not red on the base ee31e42; do not merge until green; see lane-rules

Shipped in:

• cmux NEXT nightly 1.0.0-nightly.4162918426201 (6a1595932a)
• cmux NEXT nightly 1.0.0-nightly.4163036887701 (4a7a84507f)
• cmux NEXT nightly 1.0.0-nightly.4163148939801 (96eb1b98d7)

The feat-cmux-next push run https://github.com/manaflow-ai/cmux/actions/runs/41619934635 at 092736d failed: cmux-next fleet Release compile.
Those jobs last passed at 8cc02ce. This pull request is one of 5 merged since: #33578, #33567, #33411, #33407, #33405.
If the failure is in your change, fix forward on feat-cmux-next. Pull requests run only the tiers their paths reach (docs/ci/cmux-next-tiers.md); label a batch PR full-ci to run them all before merging.

[blacksmith-sh]

Found 9 test failures on Blacksmith runners:

Failures

Test	View Logs
/tmp/tmpk0r7e09_/summary-fail.json (live):/summary-fail.json (live):	View Logs
/tmp/tmpkirqwnqn/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
convention violations found (ERROR lines above)./ convention violations found (ERROR lines above).	View Logs
the snapshot was not derived on the tip from the landed exports: schema old/ the snapshot was not derived on the tip from the landed exports: schema old	View Logs
the snapshot was not derived on the tip from the landed exports: schema old/ the snapshot was not derived on the tip from the landed exports: schema old	View Logs

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

[teamleaderleo]

Review (codex, router-review): SHIP at 4b243b6

Reviewer: codex gpt-6-astra high, fast tier.

Follow-ups: 1. Each lands as an issue in this repo that links this receipt; the lane that opened the PR fixes it forward.

SHIP at 4b243b6
Visual verdict: no images; Leo tries the build

No correctness regression found in the code review. AppKit tests could not run in this Linux box.

1. [P2] [follow-up] Packages/macOS/CmuxNext/Sources/CmuxNextDesign/PaneTabRowSharing.swift:121: No screenshots verify the native fill. Check the built app for matching toolbar color and an uninterrupted top rim.

Follow-ups:

• [P2] [follow-up] Verify the toolbar fill and rim visually on macOS.

[cmux-bot]

cmux-bot approves 4b243b6: an independent review passed this exact head (router-review receipt by teamleaderleo). A push needs a new review; a later BLOCK at this head dismisses this approval.