Initial FocusFixer implementation

Menu-bar utility that fixes cross-display keyboard focus loss: a
listen-only CGEvent tap locates the window under the cursor and
reasserts app activation + AX focus on it, with debounce, tap
auto-recovery, and an Accessibility permission gate.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

FocusFixer/WindowLocator.swift

@@ -0,0 +1,49 @@
+import CoreGraphics
+import os
+
+/// A single on-screen window as reported by the window server, reduced to
+/// the fields FocusFixer needs. Kept separate from the raw CGWindowList
+/// dictionary so the resolution logic below can be unit tested with
+/// synthetic data instead of the real window server.
+struct WindowInfo: Equatable {
+    let ownerPID: pid_t
+    let layer: Int
+    let bounds: CGRect
+}
+
+enum WindowLocator {
+    private static let logger = Logger(subsystem: "com.local.focusfixer", category: "WindowLocator")
+
+    /// Resolves the owning process ID of the frontmost on-screen window
+    /// under `point`, using the live window server state.
+    static func ownerPID(at point: CGPoint) -> pid_t? {
+        guard let list = CGWindowListCopyWindowInfo(.optionOnScreenOnly, kCGNullWindowID) as? [[String: Any]] else {
+            logger.error("CGWindowListCopyWindowInfo returned nil")
+            return nil
+        }
+        return ownerPID(at: point, in: list.compactMap(parse))
+    }
+
+    /// Pure resolution logic: `windows` is assumed to be in front-to-back
+    /// z-order, matching CGWindowListCopyWindowInfo's contract. Only
+    /// layer-0 windows (ordinary app windows, excluding menu bar, Dock,
+    /// Spotlight, and Control Center) are considered.
+    static func ownerPID(at point: CGPoint, in windows: [WindowInfo]) -> pid_t? {
+        for window in windows where window.layer == 0 && window.bounds.contains(point) {
+            return window.ownerPID
+        }
+        return nil
+    }
+
+    private static func parse(_ dict: [String: Any]) -> WindowInfo? {
+        guard
+            let pid = dict[kCGWindowOwnerPID as String] as? pid_t,
+            let layer = dict[kCGWindowLayer as String] as? Int,
+            let boundsDict = dict[kCGWindowBounds as String] as? [String: Any],
+            let bounds = CGRect(dictionaryRepresentation: boundsDict as CFDictionary)
+        else {
+            return nil
+        }
+        return WindowInfo(ownerPID: pid, layer: layer, bounds: bounds)
+    }
+}