[datlechin]

Why

Under a custom theme the inspector's field area was a warm gray slab inside an otherwise themed window. The inspector frame is AppKit glass that already takes the theme's window color, matching the sidebar. The field list is a SwiftUI List, which puts its own content-background material behind its rows, and that material never follows the window color. #3395 removed the hidden list background that used to sit there.

Change

• The inspector field list and the agent's proposed statements list hide their own background on macOS 26 and later, so the inspector glass shows through and the whole pane matches the sidebar. This is the new design's guidance for effect views inside glass split items. Before macOS 26 nothing changes.
• Applies to the main window and the Data File window.
• Under the default themes the field area now shows the inspector glass too (light: white becomes the glass gray).

Verified

SplitItemGlassBackgroundTests checks that the field list and the statements list draw no content-background material where split items are glass, and that a plain list still does without the modifier. On screen, Tokyo Night: field area (57,54,53) before, (49,48,58) after, equal to the inspector header and the sidebar.

Screenshots

Tokyo Night inspector, before and after:

Default light inspector, before and after:

Whole window, Tokyo Night, after:

Not in this PR

• SwiftUI Tables in Users & Roles and Compare sit in the detail column, not a glass item, and stay chrome (theme.md).