#29618 Agent chat: no background band behind the header tools in the tab row

Leo, 2026-10-31 19:25Z: "and we STILL havne't removed the f***ign background????" and "well the more important thing is that i literally said that stuff like 15+ hours ago"

Leo, 2026-10-31 05:00Z (the original ask): "AND THE FING BACKGROUND ON THIS FING BUILD ON THESE BUTTONS STILL ISN'T F***ING REMOVESD"

What the background is

The chat shares its pane's tab row (chrome.tabs.rowTools, on by default). Since #25638 the shell leaves that row transparent (.acpmux-shell[data-tab-row] paints transparent for the row's height) so the native strip shows behind the title and tools. But the agent chat runs in Chromium by default (agent.chromium), and a Chromium page is an opaque child window. What shows through the transparent row is the document's root surface, not the native strip. In Leo's screenshot that is a flat darker band behind the title, Session Info and Changes, ending where the pane's own fill (the native toolbar and the pane below) begins.

#28962 removed the pressed-button plates. That was a different fill, so this band stayed.

Change (removal only)

• Delete the .acpmux-shell[data-tab-row] transparent-row gradient. The shell's own background: var(--agent-page-bg) now runs to the top, so the row behind the header tools has the same fill as the pane under it and the native toolbar beside it.
• Delete the test that pinned the transparent row. No other rule, control, spacing or card changes.

Supersedes the approach in #28116 (HOLD: making html transparent does nothing in an opaque Chromium window).

Risk: low. A WebKit chat now paints the pane fill under the native tab strip instead of leaving it clear. That is the same fill as the rest of the pane.

Agent session: agent session

🤖 Generated with Claude Code

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Summary by cubic

Removes the transparent tab-row band in the agent chat so the header tools now sit on the same fill as the rest of the pane.

In Chromium the chat is an opaque child window, so the transparent row showed the document's root surface instead of the native strip, producing a darker band behind the title, Session Info, and Changes. Deleting the gradient lets the pane's own background run to the top, and removes the test that pinned the transparent row.

Risk is low; a WebKit chat now paints the pane's fill under the native tab strip instead of leaving it clear.