The board wears a picture — background becomes a mapping, and the window chrome follows it under a thin frost

background is {color:, image:} and only a mapping at every level; the board's image paints the full window under a transparent title bar, with a thin-material frost strip keeping the chrome legible and the standard accommodations intact.

Claude-Session: https://claude.ai/code/session_014PtZdPwqZuqEDLc6wZMtEy

KanbanTests/UndoWriteTests.swift

@@ -41,7 +41,7 @@ schema: 1
 title: Styled
 order: 3072
 project: lanework       # agent overlay
-background: blue
+background: {color: blue}
 icon: star
 created: 2026-01-01T09:00:00Z
 ---
@@ -991,7 +991,7 @@ private enum Foreign {
 
     static func restyle(_ fixture: WriterFixture, _ path: String, background: String) throws {
         try BoardWriter.updateIndex(inItemFolder: fixture.url(path), operation: .style(title: nil)) { document in
-            document.set(FrontmatterKeys.background, to: .string(background))
+            document.setStyleValue(background, for: FrontmatterKeys.background)
         }
     }