Lay out Bento again when the work area changes back before settling

Sources/BetterTileCore/AmbientLayoutReconciler.swift

@@ -43,8 +43,9 @@ public enum AmbientLayoutTransition: Sendable {
     /// The single-window latch fired in any layout mode.
     case placeSingleWindow(session: LayoutSession, placement: Placement)
     /// Apply the derived Bento placements. A work area requests authoritative
-    /// settlement after a successful commit and deliberately remains absent
-    /// from `session.lastWorkArea` until that settlement succeeds.
+    /// settlement after a successful commit. It waits in
+    /// `session.pendingWorkArea` and reaches `session.lastWorkArea` only when
+    /// that settlement succeeds.
     case applyLayout(session: LayoutSession, placements: [Placement], settleWorkArea: BTRect?)
 
     public var session: LayoutSession {
@@ -88,9 +89,9 @@ public struct AmbientLayoutReconciler: Sendable {
         var session = original
         let before = session.bentoState
         let frames = Dictionary(uniqueKeysWithValues: observation.windows.map { ($0.id, $0.frame) })
-        let workAreaChanged = session.lastWorkArea.map {
-            !$0.approximatelyEquals(observation.display.visibleFrame, tolerance: 0.5)
-        } ?? false
+        let workAreaChanged = [session.lastWorkArea, session.pendingWorkArea].contains { area in
+            area.map { !$0.approximatelyEquals(observation.display.visibleFrame, tolerance: 0.5) } ?? false
+        }
 
         var shouldApply = false
         if session.mode == .bento, !session.automaticWritesSuspended {
@@ -170,7 +171,9 @@ public struct AmbientLayoutReconciler: Sendable {
             : nil
 
         session.lastObservedFrames = frames
-        if settleWorkArea == nil {
+        if let settleWorkArea {
+            session.pendingWorkArea = settleWorkArea
+        } else {
             session.lastWorkArea = observation.display.visibleFrame
         }
 

Sources/BetterTileCore/LayoutSessions.swift

@@ -56,7 +56,13 @@ public struct LayoutSession: Hashable, Sendable {
     public var excludedFocusWindowIDs: Set<WindowID>
     public var bentoReinsertionAnchors: [WindowID: BentoReinsertionAnchor]
     public var lastObservedFrames: [WindowID: BTRect]
-    public var lastWorkArea: BTRect?
+    /// The work area the layout was last confirmed for.
+    public var lastWorkArea: BTRect? {
+        didSet { pendingWorkArea = nil }
+    }
+    /// The work area of a layout written but not yet confirmed. The windows
+    /// already moved for it, so changing back to `lastWorkArea` is a change.
+    public var pendingWorkArea: BTRect?
     public var isBentoInitialized: Bool
     public var hasAppliedSingleWindowPlacement: Bool
     /// Corroborates a window's disappearance before its pane is given up.

Tests/BetterTileCoreTests/AmbientLayoutReconcilerTests.swift

@@ -616,3 +616,43 @@ func aTemporarilyMissingBentoPeerDoesNotMaximizeTheRemainingWindow(knownMember:
     }
     #expect(stableSession == thirdSession)
 }
+
+/// The work area changes and changes back before the first layout settles,
+/// as when a display or Dock change is undone quickly. The windows already
+/// moved for the first change, so the change back must lay them out again.
+@Test func aWorkAreaThatChangesBackBeforeSettlingIsAppliedAgain() throws {
+    let windows = [ambientLeft, ambientRight]
+    let smaller = BTRect(x: 0, y: 0, width: 1_200, height: 720)
+    let session = LayoutSession(
+        displayID: ambientDisplayID,
+        mode: .bento,
+        bentoState: horizontalPaneState(windows),
+        windowIDs: Set(windows.map(\.id)),
+        bentoInsertionOrder: windows.map(\.id),
+        lastWorkArea: ambientBounds
+    )
+    let reconciler = ambientReconciler()
+    let shrink = reconciler.transition(
+        session: session,
+        observation: ambientObservation(
+            windows: windows,
+            display: DisplaySnapshot(id: ambientDisplayID, frame: ambientBounds, visibleFrame: smaller)
+        )
+    )
+    guard case let .applyLayout(shrunk, placements, _) = shrink else {
+        Issue.record("A smaller work area must apply the layout")
+        return
+    }
+    let moved = windows.map { window in
+        var window = window
+        window.frame = placements.first { $0.windowID == window.id }?.frame ?? window.frame
+        return window
+    }
+
+    let back = reconciler.transition(session: shrunk, observation: ambientObservation(windows: moved))
+    guard case let .applyLayout(_, restored, _) = back else {
+        Issue.record("The work area changed back, so the windows must be laid out for it again")
+        return
+    }
+    #expect(restored.allSatisfy { $0.frame.maxY == ambientBounds.maxY })
+}