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/UI/Card/CardToolbar.swift

@@ -6,6 +6,7 @@ extension NSToolbarItem.Identifier {
     static let cardEditBody = Self("card.editBody")
     static let cardRawSource = Self("card.rawSource")
     static let cardAddAttachment = Self("card.addAttachment")
+    static let cardShowSidebar = Self("card.showSidebar")
 }
 
 // MARK: - The card window's toolbar
@@ -15,9 +16,12 @@ extension NSToolbarItem.Identifier {
 /// "**Card window default: Edit Body · Raw Source · Add Attachment** — the window's three committed
 /// functions, all discoverable from its toolbar; the catalog is the same trio." So the default set
 /// *is* the catalog here, and Customize offers rearrangement and removal rather than a choice of
-/// items — which is exactly what a window with three functions should offer.
+/// items — which is exactly what a window with three functions should offer. **Show Sidebar joined
+/// them** (05-card-window.md ▸ Composition, the toggle added beside the toolbar-customization work):
+/// a fourth default item, the trailing sidebar's own show/hide control, the `Show Trash` precedent
+/// applied to the card window's one collapsible pane.
 ///
-/// ### The three items are the three menu rows, predicates included
+/// ### The four items are the four menu rows, predicates included
 ///
 /// - **Edit Body** is "a single toggle button (on-state in Edit — mirroring the View ▸ Edit Body
 ///   checkmark)", and it disables while source mode is active. That clause is not restated here: the
@@ -31,6 +35,12 @@ extension NSToolbarItem.Identifier {
 ///   `index.md`, so they're safe alongside a raw edit". Its predicate is likewise the row's own
 ///   (`AddAttachmentCommand.isEnabled`), which is scope plus the read-only lock and says nothing
 ///   about the body's mode.
+/// - **Show Sidebar** is a toggle showing on-state too, mirroring the View ▸ Show Sidebar checkmark
+///   (`ShowSidebarCommand`) — and it is the one item here with no window-scoped handle behind it:
+///   its predicate reads `AppPreferences.showCardSidebar` straight off `UserDefaults`, the same
+///   app-wide, persisted bit `CardWindowView` renders from and every card window's toolbar answers
+///   to alike. Always enabled, `ShowCommentsCommand`'s own posture: showing or hiding a pane is not a
+///   mutation, so the read-only lock has no say in it.
 ///
 /// Labels are the menu titles minus a trailing ellipsis, so File ▸ Add Attachment… labels as **Add
 /// Attachment** (03's own example).
@@ -39,17 +49,28 @@ enum CardToolbar {
 
     static let identifier = "dev.rzen.indie.Kanban.card"
 
-    /// "The catalog is the same trio" — so the defaults are the catalog, in 03's order.
+    /// "The catalog is the same trio" plus Show Sidebar — so the defaults are the whole catalog, in
+    /// this file's order.
     static let defaultItems: [NSToolbarItem.Identifier] = [
         .cardEditBody,
         .cardRawSource,
         .cardAddAttachment,
+        .cardShowSidebar,
     ]
 
+    /// - Parameters:
+    ///   - isSidebarShown: Show Sidebar's read, defaulted to the real bit
+    ///     (`AppPreferences.showCardSidebar`). Injectable so a test can drive the item without
+    ///     touching the developer's own `UserDefaults.standard` domain — `StyleRecents`' own caution,
+    ///     applied to the one item here with no window-scoped handle to hold a scratch value instead.
+    ///   - setSidebarShown: Show Sidebar's write, defaulted to the real setter
+    ///     (`AppPreferences.setShowCardSidebar`), for the same reason.
     static func specs(
         body: CardBodyPresentation,
         rawSource: CardRawSourceSession,
-        attachments: CardAttachments
+        attachments: CardAttachments,
+        isSidebarShown: @escaping () -> Bool = { AppPreferences.showCardSidebar },
+        setSidebarShown: @escaping (Bool) -> Void = { AppPreferences.setShowCardSidebar($0) }
     ) -> [ToolbarItemSpec] {
         [
             .mirroring(
@@ -90,17 +111,38 @@ enum CardToolbar {
                     perform: { [weak attachments] in attachments?.add() }
                 )
             ),
+            // **The one item here with no window-scoped handle** — its read and write are the two
+            // injected closures above, defaulted to `AppPreferences.showCardSidebar` /
+            // `.setShowCardSidebar`, the plain `UserDefaults`-backed bit every card window's sidebar
+            // (`CardWindowView`) and View ▸ Show Sidebar row (`ShowSidebarCommand`) already read and
+            // write the same way. `sidebar.right` is the trailing variant: the sidebar this toggles
+            // sits on the window's trailing edge (05-card-window.md ▸ Composition), never the leading
+            // one the plain `sidebar.left` glyph would imply.
+            .mirroring(
+                menuTitle: "Show Sidebar",
+                identifier: .cardShowSidebar,
+                symbol: "sidebar.right",
+                behavior: .toggle(isEnabled: { true }, isOn: isSidebarShown, setOn: setSidebarShown)
+            ),
         ]
     }
 
     static func controller(
         body: CardBodyPresentation,
         rawSource: CardRawSourceSession,
-        attachments: CardAttachments
+        attachments: CardAttachments,
+        isSidebarShown: @escaping () -> Bool = { AppPreferences.showCardSidebar },
+        setSidebarShown: @escaping (Bool) -> Void = { AppPreferences.setShowCardSidebar($0) }
     ) -> WindowToolbarController {
         WindowToolbarController(
             identifier: identifier,
-            specs: specs(body: body, rawSource: rawSource, attachments: attachments),
+            specs: specs(
+                body: body,
+                rawSource: rawSource,
+                attachments: attachments,
+                isSidebarShown: isSidebarShown,
+                setSidebarShown: setSidebarShown
+            ),
             defaults: defaultItems
         )
     }