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/History/HistoryPhrase.swift

@@ -55,6 +55,20 @@ public enum HistoryPhrase {
         case reorder = "Reorder"
         case rename = "Rename"
         case restyle = "Restyle"
+
+        /// A card's `labels` list rewritten — the sidebar's chips and the context menu's submenu
+        /// (`FrontmatterKeys.labels`, activated 2026-08-09; `BoardStore.setLabels(_:onCard:on:)`).
+        ///
+        /// **Its own verb rather than `restyle`**, on `collapse`'s reasoning: the row has to read back
+        /// the gesture it undoes, and "Undo Restyle Card" after clicking a label would name a control
+        /// the user never touched. The word is 06-history-undo.md ▸ Commit messages' own for a change
+        /// to this key — the composer has said "Relabel card 'X'" since before there was a control to
+        /// press (`ChangeNarrator`) — so the menu row and the change journal now speak the same one.
+        ///
+        /// **One verb for both directions**, unlike `collapse`/`expand`: adding and removing a label
+        /// are the same control pressed twice, where collapsing and expanding are two menu rows with
+        /// two words.
+        case relabel = "Relabel"
         case resize = "Resize"
         /// A lane folded to its slim strip (03-board-ui.md § Lane ▸ Collapsed lanes).
         ///

Kanban/History/HistoryStaleness.swift

@@ -55,6 +55,20 @@ public enum ExpectedField: Sendable, Equatable {
     /// everywhere else here.
     case hero(String?)
 
+    /// `labels` — the card's label list, whole (`BoardStore.setLabels(_:onCard:on:)`, the key's
+    /// 2026-08-09 activation).
+    ///
+    /// **The whole list, not one label**, which is what makes the comparison right: a labels write
+    /// rewrites the key's entire value, so the after-value it declares is the entire value it wrote. A
+    /// per-label expectation would let a step that added `bug` cross safely onto a card somebody else
+    /// has since retagged completely, which is exactly the foreign edit staleness exists to catch.
+    ///
+    /// `nil` is the removed key — what taking the last label off leaves behind (the remove-at-default
+    /// family; `FrontmatterKeys.labels`). A card whose list has been emptied but whose key survives for
+    /// preserved non-name entries reads `.valid([])` and matches `[]`, not `nil`: those are different
+    /// bytes and the step knows which one it wrote.
+    case labels([String]?)
+
     /// `icon` — the styling gesture's symbol dimension.
     case icon(String?)
 
@@ -79,6 +93,7 @@ public enum ExpectedField: Sendable, Equatable {
         case .background: .background
         case .backgroundImage: .backgroundImage
         case .hero: .hero
+        case .labels: .labels
         case .icon: .icon
         case .iconColor: .iconColor
         case .body: .body
@@ -95,6 +110,7 @@ public enum ExpectedField: Sendable, Equatable {
         case background
         case backgroundImage
         case hero
+        case labels
         case icon
         case iconColor
         case body
@@ -360,6 +376,7 @@ public enum HistoryStaleness {
         case let .background(expected): equal(document.background, expected)
         case let .backgroundImage(expected): equal(document.backgroundImage, expected)
         case let .hero(expected): equal(document.hero, expected)
+        case let .labels(expected): equal(document.labels, expected)
         case let .icon(expected): equal(document.icon, expected)
         case let .iconColor(expected): equal(document.iconColor, expected)
         case let .body(expected): document.body == expected