A reserved key comes to life — the card window's sidebar grows a Labels section, and labels stops being somebody else's

`labels` has been a reserved tracker key since the rewrite: preserved verbatim, never
interpreted, drawn only as an anonymous row in the Details section beside `assignees` and
`due`. The owner's cards claim it for first-party use, so it joins the schema — read
leniently (a list of names, a bare scalar coercing to one, a mapping malformed and
preserved), written canonically (a quoted flow list in the order the user arranged, no
auto-sort), and removed outright when the last label goes, the way an expanded lane drops
`collapsed`.

Identity is case-insensitive and display is case-preserving, so a card carries `bug` once
however many ways the board spells it, and entries the reading cannot name ride through the
write untouched at the tail.

The section sits second, above Details — which is the point rather than a layout preference:
Details is where keys the app does *not* own are shown, and this key just stopped being one.
Rows rather than chips, because the sidebar is twenty-six characters wide. The add field
autocompletes against the board's own used-labels universe, derived from every live and
trashed card with no store beside the files, and says out loud when Return would mint a word
the board has never used.

Writes ride a `.relabel` operation of their own, because the commit composer has said
"Relabel card 'X'" since long before there was a control to press — and now the undo row says
it too.

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

Kanban/App/AppModel.swift

@@ -169,6 +169,14 @@ public enum AppPreferences {
     /// the key is declared here with its neighbours for `WindowID`'s reason.
     public static let quickStyleBackgroundsKey = "quickStyleBackgrounds"
 
+    /// **The recently applied labels** — the tie-break half of the card menu's "most frequently and
+    /// recently used" twelve (`LabelRecents`, which owns the list rule; `LabelRanking`;
+    /// `FrontmatterKeys.labels`, activated 2026-08-09). `quickStyleBackgroundsKey`'s neighbour in every
+    /// respect: an array of strings, most-recent-first, app-wide, a user preference and never board
+    /// data — the labels a board *has* are derived from its own cards (`LabelIndex`), and this is only
+    /// a memory of what this user reached for.
+    public static let labelRecentsKey = "labelRecents"
+
     /// **The board's zoom level** — "app-wide and persisted across restarts" (11-command-nexus.md
     /// ▸ View ▸ Actual Size; 03-board-ui.md ▸ Layout — zoom). A rung on `BoardZoom.levels`, stored as
     /// the multiplier itself. Read and written by `BoardZoomStore`, which owns the ladder's rules; the
@@ -347,6 +355,12 @@ public final class AppModel {
     /// board-scoped and this list deliberately is not.
     public let styleRecents: StyleRecents
 
+    /// The recently applied labels, app-wide (`LabelRecents`; `FrontmatterKeys.labels`). Owned here
+    /// for `styleRecents`' reason exactly — app-scoped, persisted beside it, and reached by the card
+    /// context menu and the card window's sidebar through the environment, since a `BoardStore` is
+    /// board-scoped and this list deliberately is not.
+    public let labelRecents: LabelRecents
+
     /// The board's app-wide zoom level (03-board-ui.md ▸ Layout — zoom). Owned here for
     /// `styleRecents`' reason exactly: app-scoped, persisted beside it, and reached by every board
     /// window through the environment — while the menu rows and the toolbar buttons, which live
@@ -688,6 +702,7 @@ public final class AppModel {
     ) {
         boardRegistry = BoardRegistry(storageURL: registryStorageURL)
         styleRecents = StyleRecents(defaults: preferences)
+        labelRecents = LabelRecents(defaults: preferences)
         zoom = BoardZoomStore(defaults: preferences)
         appearance = AppearanceStore(defaults: preferences)
         printProfiles = PrintProfileStore(defaults: preferences)

Kanban/App/CardWindowHost.swift

@@ -492,6 +492,9 @@ struct CardWindowHost: View {
                 // editor feeds are app-wide state (02-architecture.md § Per-board app state), so
                 // they come from the model every window shares rather than from this board's store.
                 recents: appModel.styleRecents,
+                // The same argument one field over: the labels this user reached for lately are
+                // app-wide state (`LabelRecents`), so they come from the model every window shares.
+                labelRecents: appModel.labelRecents,
                 cardFolder: Self.cardFolder(root: store.rootURL, placement: placement),
                 bodyPresentation: bodyPresentation,
                 bodySession: session.body,