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/CardWindowHost.swift

@@ -302,6 +302,12 @@ struct CardWindowHost: View {
     /// threading the pair through a view that would then have to publish them back up.
     @AppStorage(AppPreferences.showCommentsKey) private var showComments = true
     @AppStorage(AppPreferences.commentsBesideBodyKey) private var commentsBesideBody = true
+    /// The sidebar's own visibility bit, read here for `showComments`' one reason: the window's
+    /// **minimum size** depends on it too (`minimumSize`). The toolbar item reads
+    /// `AppPreferences.showCardSidebar` directly (`CardToolbar`, an AppKit seam with no `@AppStorage`
+    /// of its own), and `CardWindowView` reads this same key again itself — three readers of one
+    /// `UserDefaults` key, `showComments`' own arrangement.
+    @AppStorage(AppPreferences.showCardSidebarKey) private var showSidebar = true
 
     private enum Phase {
         case opening
@@ -426,15 +432,23 @@ struct CardWindowHost: View {
                 isClosePending = false
                 windowController.closeAfterFlush()
             }
+            // **The toolbar's Show Sidebar item, nudged fresh** — `WindowToolbarController`'s own
+            // observation tracking only sees `@Observable` reads (its header explains why: menu
+            // commands and AppKit have no `@Environment` to poll), and `AppPreferences.showCardSidebar`
+            // is a plain `UserDefaults` read, not one. The toolbar's own click already revalidates
+            // itself (`toggleFired`); this is the same nudge for the View-menu row's write, which is
+            // the only other place this bit changes.
+            .onChange(of: showSidebar) { _, _ in windowController.revalidateToolbar() }
             .onDisappear { finish() }
     }
 
-    /// **The minimum grows only while the comments pane is beside the body** (05-card-window.md ▸
-    /// Composition) — which is the whole reason the stacked mount exists, so a narrow display keeps
-    /// the minimum it always had.
+    /// **The minimum grows only while the comments pane is beside the body, and shrinks while the
+    /// sidebar is hidden** (05-card-window.md ▸ Composition) — the stacked mount's own reason, and
+    /// View ▸ Show Sidebar's mirror of it: a window with neither costs the width of neither.
     private var minimumSize: CGSize {
         CardWindowMetrics.minimumSize(
             bodyPointSize: CardWindowMetrics.bodyPointSize,
+            sidebar: showSidebar,
             commentsColumn: showComments && commentsBesideBody
         )
     }
@@ -915,8 +929,11 @@ struct CardWindowHost: View {
 
         // The window's customizable toolbar — Edit Body · Raw Source · Add Attachment, "the
         // window's three committed functions" (03-board-ui.md ▸ Toolbar; 05-card-window.md ▸
-        // Window). It carries the three window-scoped handles above rather than a store, which is
-        // why it is installed here and not at attach: those are this window's, and so is it.
+        // Window), joined by Show Sidebar (below). It carries the three window-scoped handles above
+        // rather than a store, which is why it is installed here and not at attach: those are this
+        // window's, and so is it. Show Sidebar needs none of them — its read and write default to
+        // `AppPreferences.showCardSidebar` / `.setShowCardSidebar`, the same app-wide bit every card
+        // window answers to, so this call leaves the two injectable parameters unnamed.
         windowController.installToolbar(
             CardToolbar.controller(body: bodyPresentation, rawSource: rawSource, attachments: attachments)
         )