A card window toolbar control shows and hides the trailing sidebar — View ▸ Show Sidebar joins Edit Body, Raw Source and Add Attachment

The card window's trailing attributes sidebar has always been unconditional
since m6; this adds View ▸ Show Sidebar (a checkmark toggle, ShowComments'
shape) and a matching toolbar item on the customizable card toolbar
(NSToolbar/WindowToolbarController), a fourth default beside Edit Body,
Raw Source and Add Attachment. sidebar.right for the trailing pane; one
shared animated write path (AppPreferences.setShowCardSidebar) both faces
call, structural-voice reflow with a trailing slide-and-fade transition
(Motion.cardSidebarTransition), Reduce Motion respected throughout.

CardWindowMetrics.minimumSize gains a sidebar: Bool = true parameter so a
hidden sidebar shrinks the window's floor, composing with the existing
commentsColumn parameter. The toolbar item's read/write are injectable
closures (defaulted to the real UserDefaults-backed pair) so its plumbing
is testable without touching the developer's own preferences domain.
WindowToolbarController's observation tracking only sees @Observable
reads, so a small HostedWindowController.revalidateToolbar() plus an
onChange nudge keeps the toolbar button's on-state in step with the
View-menu row's write.

Scope held narrowly to visibility, per the card: no sidebar section
reordering, no action-moving.

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

Kanban/App/WindowAccessor.swift

@@ -230,6 +230,16 @@ final class HostedWindowController: NSObject, NSWindowDelegate {
         window.toolbar = nil
     }
 
+    /// Re-validates this window's toolbar items against their current predicates, on demand.
+    ///
+    /// `WindowToolbarController`'s own observation tracking (`trackValidationState`) only notices
+    /// `@Observable` reads changing; a predicate that reads a plain `UserDefaults`-backed bit instead
+    /// (`AppPreferences.showCardSidebar`, `CardToolbar`) is invisible to it. A no-op before a toolbar
+    /// exists, which covers every window kind that has none.
+    func revalidateToolbar() {
+        toolbarController?.revalidate()
+    }
+
     // MARK: Title visibility
 
     /// Hides this window's title from the title bar, leaving the toolbar exactly as it renders today