Drop pill border on single-icon voice/dictation toggle

[Copilot]

Description

When only one of the voice/dictation buttons is present, the segmented-icon toggle still rendered its housing border, boxing a lone button in a way that's inconsistent with VS Code's other borderless input controls.

The control is built on the generic segmented-icon-toggle chrome. When exactly one cell is present, voiceInputModeActionViewItem already tags the container with single, but nothing cleared the now-meaningless divider border.

• segmentedIconToggle.css: hide the housing border in the single-icon view.

.monaco-segmented-icon-toggle-container.single .monaco-segmented-icon-toggle {
	border-color: transparent;
}

Uses border-color: transparent (not border: none) so the border box still occupies space, keeping width/layout stable across single ↔ multi transitions. The divider border is unchanged when two or more cells are shown. Applies to both the main chat input and the Agents window since they share the component.

• Fixes If you only have 1 of the voice buttons active I don't think the border makes sense #328794

[Copilot]

Pull request overview

Removes unnecessary chrome around a lone voice/dictation action while preserving stable control dimensions.

Changes:

• Makes the segmented-toggle housing border transparent in single-icon mode.
• Retains border-box spacing across single/multi transitions.

Show a summary per file

File	Description
src/vs/base/browser/ui/segmentedIconToggle/segmentedIconToggle.css	Hides the housing border for single-icon toggles.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 0
• Review effort level: Balanced