Follow frontmost app when placing new windows

Sources/DefiMacOS/MacOSPlatform+Snapshot.swift

@@ -38,9 +38,6 @@ extension SnapshotEngine {
   ) -> DesktopSnapshot {
     let snapshotStartedAt = ProcessInfo.processInfo.systemUptime
     let explicitlyDestroyedWindowIDs = consumeExplicitlyDestroyedWindows()
-    let frontmostProcessID = onMain {
-      _ in NSWorkspace.shared.frontmostApplication
-    }?.processIdentifier
     let tracesWindowTopology = windowTopologyEventPending
     let capturedTopologyRequiresFullSnapshot =
       windowTopologyRequiresFullSnapshot
@@ -648,7 +645,13 @@ extension SnapshotEngine {
         "frame commit observed settled=\(settledCommitLatenciesMS.count) deferred=\(deferredMismatchCount) max_latency_ms=\(maximumSettledLatencyMS, format: .fixed(precision: 2))"
       )
     }
-    let focusedWindowID = focusedWindowID(in: windows)
+    let frontmostProcessID = onMain {
+      _ in NSWorkspace.shared.frontmostApplication
+    }?.processIdentifier
+    let focusedWindowID = focusedWindowID(
+      in: windows,
+      frontmostProcessID: frontmostProcessID
+    )
     lastNativeFocusedWindowID = focusedWindowID
     verifiedNativeFocusedWindowID = focusedWindowID
     if let focusedWindowID,

Sources/DefiMacOS/SnapshotEngine.swift

@@ -849,9 +849,9 @@ extension SnapshotEngine {
   }
 
   func focusedWindowID(
-    in windows: [Window]
+    in windows: [Window],
+    frontmostProcessID: pid_t?
   ) -> WindowID? {
-    let frontmostProcessID = onMain { _ in NSWorkspace.shared.frontmostApplication }?.processIdentifier
     let system = AXUIElementCreateSystemWide()
     let focusedApplication: CFTypeRef? = AXMessagingTimeoutAccess.shared
       .withTimeout(

Sources/DefiRuntime/WindowReconciliation.swift

@@ -63,15 +63,12 @@ public func discoverWindow(
   else {
     throw ReducerError.unknownWorkspace(workspaceID)
   }
-  // Policy: a managed window spawning into the active workspace of its
-  // monitor always inserts after the focused column and takes focus - the
-  // native focused-window event can legitimately lag window creation, so it
-  // alone must not gate this.
+  // Policy: a managed window spawned by the frontmost application follows
+  // its assigned workspace and takes focus. The native focused-window event
+  // can legitimately lag window creation, so it alone must not gate this.
   let followsFocus =
     followFocusIntent
-    || (isFrontmostAppSpawn
-        && workspaceID == state.monitors[monitorIndex].activeWorkspace
-        && !window.floating)
+    || (isFrontmostAppSpawn && !window.floating)
 
   if window.floating && !window.forceTiling {
     state.monitors[monitorIndex].workspaces[workspaceIndex].floatingWindows.append(window.id)

Tests/DefiRuntimeTests/BackgroundWindowDiscoveryTests.swift

@@ -19,13 +19,15 @@ struct BackgroundWindowDiscoveryTests {
       appID: "editor",
       title: "Selected",
       frame: Rect(x: 0, y: 0, width: 600, height: 800),
+      processID: 7,
       monitorID: monitorID
     )
     let backgroundWindow = Window(
       id: WindowID(rawValue: 2),
       appID: "proxy",
       title: "Background",
       frame: Rect(x: 600, y: 0, width: 600, height: 800),
+      processID: 42,
       monitorID: monitorID
     )
     try discoverWindow(
@@ -39,6 +41,7 @@ struct BackgroundWindowDiscoveryTests {
       [selectedWindow, backgroundWindow],
       config: config,
       nativeFocusedWindowID: selectedWindow.id,
+      frontmostProcessID: 7,
       state: &state
     )
 

Tests/DefiRuntimeTests/PlacementPreferencesTests.swift

@@ -6,6 +6,55 @@ import Testing
 struct PlacementPreferencesTests {
   private let monitorID = MonitorID(rawValue: 1)
 
+  @Test
+  func `Frontmost application spawn follows persisted workspace`() throws {
+    let web = WorkspaceID(rawValue: "web")
+    let config = Config(workspaces: WorkspacesConfig(names: ["dev", web.rawValue]))
+    var state = RuntimeState(config: config)
+    state.attachMonitor(monitorID)
+    let selected = Window(
+      id: WindowID(rawValue: 1),
+      appID: "com.example.Editor",
+      title: "Editor",
+      frame: Rect(x: 0, y: 0, width: 600, height: 800),
+      processID: 7,
+      monitorID: monitorID
+    )
+    let launched = Window(
+      id: WindowID(rawValue: 2),
+      appID: "com.example.Chat",
+      title: "Chat",
+      frame: Rect(x: 600, y: 0, width: 600, height: 800),
+      processID: 42,
+      monitorID: monitorID
+    )
+    let preferences = PlacementPreferences(
+      applications: [
+        "com.example.chat": WindowPlacementPreference(
+          workspaceID: web,
+          monitorID: monitorID
+        )
+      ]
+    )
+    try discoverWindow(
+      selected,
+      decision: RuleDecision(followFocus: true),
+      isNativelyFocused: true,
+      state: &state
+    )
+
+    reconcileWindows(
+      [selected, launched],
+      config: config,
+      placementPreferences: preferences,
+      frontmostProcessID: 42,
+      state: &state
+    )
+
+    #expect(state.monitors[0].activeWorkspace == web)
+    #expect(state.selectedWindowID(on: monitorID) == launched.id)
+  }
+
   @Test
   func `Reconcile restores persisted application workspace`() throws {
     let config = Config(workspaces: WorkspacesConfig(names: ["dev", "web"]))