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/WriteFidelityTests.swift

@@ -146,7 +146,7 @@ struct WriteFidelityMinimalTouchTests {
         try step("style write", targeting: ["\(Ident.lane1)/\(Ident.card2)"]) {
             try BoardWriter.updateIndex(
                 inItemFolder: fixture.url("\(Ident.lane1)/\(Ident.card2)"), operation: .style(title: nil)
-            ) { $0.set(FrontmatterKeys.background, to: .string("blue")) }
+            ) { $0.setStyleValue("blue", for: FrontmatterKeys.background) }
         }
         try step("rename", targeting: ["\(Ident.lane2)/\(Ident.card3)"]) {
             try BoardWriter.updateIndex(