The app learns Appearance — Auto, Light, Dark from the View menu and a toolbar pull-down

View ▸ Appearance (11-command-nexus.md): three radio-exclusive rows,
app-wide, persisted, needing no window in front — the View menu's new
last group. AppearanceStore owns the override's rules (absent key =
Auto, lenient reads degrade to Auto, remove-at-default) with an
injectable apply seam so test hosts never touch NSApp; the one real
apply hands NSApp.appearance its answer in applicationDidFinishLaunching,
the global side effect KanbanApp.init must not carry. The board toolbar
gains its first .picker item — an NSMenuToolbarItem whose rows re-fetch
their spec fresh, checkmark read at menu-open like every other menu row —
and Appearance joins the search field as the second default item,
centered beside it (03-board-ui.md ▸ Toolbar, ratified 2026-08-07).

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

Kanban/UI/Board/BoardToolbar.swift

@@ -11,16 +11,18 @@ extension NSToolbarItem.Identifier {
     static let boardShowTrash = Self("board.showTrash")
     static let boardZoomIn = Self("board.zoomIn")
     static let boardZoomOut = Self("board.zoomOut")
+    static let boardAppearance = Self("board.appearance")
 }
 
 // MARK: - The board window's toolbar
 
 /// The board window's toolbar (03-board-ui.md ▸ Toolbar).
 ///
-/// ### The default is one item, and the catalog is five more
+/// ### The default is the search field and Appearance, and the catalog is the rest
 ///
-/// "**Board window default: the search field, nothing else** — trailing, the one default item; the
-/// titlebar stays clean." The flexible space ahead of it is what "trailing" means to `NSToolbar`.
+/// "**Board window default: the search field and Appearance** — both **centered**, the titlebar's
+/// view-controls cluster." The flexible space ahead of the pair is what keeps them off the leading
+/// edge before `centeredItemIdentifiers` takes over their placement.
 ///
 /// "**Catalog** (available via Customize): New Card, New Lane, Zoom In, Zoom Out …, Undo, Redo …,
 /// Show Trash (toggle state matching the View menu checkmark)." Every one of them is the *same command* as its menu row
@@ -54,8 +56,14 @@ enum BoardToolbar {
     /// than one window's — Finder's behaviour, and the reason the identifier is a constant.
     static let identifier = "dev.rzen.indie.Kanban.board"
 
-    /// "The search field, nothing else — trailing, the one default item."
-    static let defaultItems: [NSToolbarItem.Identifier] = [.flexibleSpace, .boardSearch]
+    /// "The search field and Appearance — both centered, immediately after the field
+    /// (03-board-ui.md ▸ Toolbar, the view-controls cluster)."
+    static let defaultItems: [NSToolbarItem.Identifier] = [.flexibleSpace, .boardSearch, .boardAppearance]
+
+    /// The Appearance picker's rows, in menu order — the one place index and meaning are joined, so
+    /// `specs(...)`'s `selected`/`select` closures and this array can never name two different
+    /// orderings of the same three choices.
+    private static let appearanceOptions: [AppAppearance?] = [nil, .light, .dark]
 
     /// - Parameters:
     ///   - zoom: the app-wide zoom level, in the catalog order the palette shows. It is not the
@@ -64,12 +72,15 @@ enum BoardToolbar {
     ///     `UserDefaults` at build time, since `WindowToolbarController.trackValidationState` re-arms
     ///     observation over each spec's `isEnabled` and a plain scalar would leave Zoom In looking live
     ///     at the top rung.
+    ///   - appearance: the app-wide appearance override, `zoom`'s reason exactly — not the store's,
+    ///     and `@Observable` so the picker's checkmark, read when its menu opens, is never stale.
     ///   - session: the app's drag session, for the same guard the menu rows carry
     ///     (`ZoomCommands.isEnabled`).
     static func specs(
         store: BoardStore,
         search: BoardSearchPresentation,
         zoom: BoardZoomStore,
+        appearance: AppearanceStore,
         session: DragSession
     ) -> [ToolbarItemSpec] {
         [
@@ -141,6 +152,31 @@ enum BoardToolbar {
                     setOn: { [weak store] shown in store?.setTrashVisible(shown) }
                 )
             ),
+            // A pull-down rather than a toggle: Auto/Light/Dark is a three-way exclusive choice, not
+            // an on/off bit. The one default (and centered) catalog item beside the field
+            // (`defaultItems`, `controller(...)`'s `centeredItemIdentifiers`), always enabled — an
+            // appearance override needs no board state, exactly as the View-menu row needs no board
+            // window (`AppearanceCommands`).
+            .mirroring(
+                menuTitle: "Appearance",
+                identifier: .boardAppearance,
+                symbol: "circle.lefthalf.filled",
+                behavior: .picker(
+                    options: [
+                        (title: "Auto", symbol: nil),
+                        (title: "Light", symbol: nil),
+                        (title: "Dark", symbol: nil),
+                    ],
+                    selected: { [weak appearance] in
+                        guard let appearance else { return nil }
+                        return appearanceOptions.firstIndex(of: appearance.override)
+                    },
+                    select: { [weak appearance] index in
+                        guard appearanceOptions.indices.contains(index) else { return }
+                        appearance?.setOverride(appearanceOptions[index])
+                    }
+                )
+            ),
             .staticLabel(
                 "Search",
                 identifier: .boardSearch,
@@ -180,18 +216,21 @@ enum BoardToolbar {
         store: BoardStore,
         search: BoardSearchPresentation,
         zoom: BoardZoomStore,
+        appearance: AppearanceStore,
         session: DragSession
     ) -> WindowToolbarController {
         let controller = WindowToolbarController(
             identifier: identifier,
-            specs: specs(store: store, search: search, zoom: zoom, session: session),
+            specs: specs(store: store, search: search, zoom: zoom, appearance: appearance, session: session),
             defaults: defaultItems
         )
         // Centered against the window, not a flexible-space sandwich (03 ▸ Toolbar's placement
         // grammar, ratified 2026-08-06): `centeredItemIdentifiers` holds as catalog items install
         // and sits outside the autosaved configuration, so it reaches machines that saved an
-        // arrangement under the old trailing default. `defaultItems` is untouched.
-        controller.toolbar.centeredItemIdentifiers = [.boardSearch]
+        // arrangement under the old trailing default. `defaultItems` is untouched. Appearance joined
+        // the cluster after search (`defaultItems`'s own order), so the two center together as one
+        // group — search first, Appearance beside it — rather than as two independently-placed items.
+        controller.toolbar.centeredItemIdentifiers = [.boardSearch, .boardAppearance]
         controller.onInstalledItemsChanged = { [weak search] identifiers in
             search?.isInstalledInToolbar = identifiers.contains(.boardSearch)
         }