PR #32687 - manaflow-ai/cmux

Leo (2026-11-02): "I'VE LITERALLY FING ASKED / FOR THE FING STUPID BACKGROUND ON THE FING TOP RIGHT ICONS TO BE REMOVED / FOR FING / WEEKS". Earlier (2026-10-31): "AND THE FING BACKGROUND ON THIS FING BUILD ON THESE BUTTONS STILL ISN'T F***ING REMOVESD".

What was drawing it

With the chat's tools in the pane's tab row (chrome.tabs.rowTools, on by default), the page is transparent at html but .acpmux-shell still painted --agent-page-bg over the whole pane, the tab row included. The tabs sit on the native row; the tools (Session Info, terminal, changes, browser, files) sat on a block of the page's color that ended at the pane's ⋯. That block is the background.

Regressed by: #20933 put the tools in the tab row while the shell kept its background. #25638 (git log -S'html:has(.acpmux-shell[data-tab-row])') made html transparent but left the shell's color. #28962 later removed per-button plates, which is why the complaint outlived it.

Change

header.css: .acpmux-shell[data-tab-row] paints the page color only below the row (a hard-stop gradient at --acpmux-tab-row-height), so the icons sit directly on the row.
Only the button under the pointer shows a hover pill. A toggle whose panel is open, or a button whose menu is open, shows the filled rounded square, as in Leo's reference, where only the toggled-on button is filled. The focus ring stays; the shared focus gradient stays off. Embedded and floating headers match.
Takes back #28962: its pressed-and-hover "no fill" was not what Leo meant. The background was the shell band, and his reference shows a fill on the toggled-on button.

Test

webviews/test/chat-header-tab-row-surface.test.ts (committed red first in 897c56f7b8c):

A new pixel test renders the shipped CSS with the tab-row shell. The pixels behind the tools must be the row's color, not --agent-page-bg, and below the row they must be the page color.
The per-state cases now assert: nothing at rest, focused or disabled; the hover pill only on hover; the on fill only while pressed or with a menu open. This covers all four header hosts.

Observed / Not run

Observed: scripts/web-lint.sh passed (fast checks; the type-aware lint is left to CI on this host).
Not run yet: the browser-lane test through cmux-ci. Results will be posted on this PR. No Mac capture yet: this VM has no fleet client.

Changelog

Fixed: The agent pane header's top-right icons no longer sit on a background; only hover and an open panel's toggle are highlighted.

Agent session: agent session

🤖 Generated with Claude Code

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Summary by cubic

Fixes the agent pane header's top-right icons showing a background band at rest, so the icons now sit directly on the tab row like the tabs beside them.

Bug Fixes

The shell paints the page color only below the tab row, not behind the tools.
Icons show no background at rest; hover shows a pill, and a toggle with an open panel or a button with an open menu shows the filled rounded square.
Reverts the previous removal of all fills on pressed states, matching the reference where only the toggled-on button is filled.