player: active foreground wait replaces fixed 600ms sleep (#14)

BringSutToForeground() now polls GetForegroundWindow() == SUT hwnd at 25ms
intervals up to 2s, followed by a 100ms tail settle, instead of the brittle
fixed 600ms sleep. First-attempt replay of box-v6.yaml is now reliable
(previously dropped the opening "BOX" keystrokes on a cold start).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/Recordingtest.Player/UiaPlayerHost.cs

@@ -212,21 +212,34 @@ public sealed class UiaPlayerHost : IPlayerHost, IDisposable
     /// was launched from a shell that still has focus when the first Type/Hotkey
     /// step fires.
     /// </summary>
+    [System.Runtime.InteropServices.DllImport("user32.dll")]
+    private static extern IntPtr GetForegroundWindow();
+
     public void BringSutToForeground()
     {
         try
         {
             var w = _app?.GetMainWindow(_automation, TimeSpan.FromSeconds(5));
             if (w is null) return;
+            var targetHwnd = w.Properties.NativeWindowHandle.ValueOrDefault;
             try { w.SetForeground(); } catch { /* best-effort */ }
             try { w.Focus(); } catch { /* best-effort */ }
-            // Small settle so the OS-level focus switch takes effect before
-            // the first SendInput. 150ms is enough in practice on Win10.
-            // Increased from 150→600ms because FlaUI Keyboard.Type drops the
-            // first couple of characters if SendInput fires before the OS
-            // finishes the focus transition (observed: "BOX" lost on first
-            // step, "10" succeeded later once the app had settled).
-            System.Threading.Thread.Sleep(600);
+
+            // Issue #14 follow-up: active wait instead of fixed 600ms sleep.
+            // Poll until the OS reports the SUT as the foreground window, up
+            // to 2s. Previously a 600ms fixed sleep was threshold-sensitive
+            // and caused the first "BOX" keystroke to get dropped on a cold
+            // first run.
+            var deadline = DateTime.UtcNow.AddSeconds(2);
+            while (DateTime.UtcNow < deadline)
+            {
+                if (targetHwnd != IntPtr.Zero && GetForegroundWindow() == targetHwnd)
+                    break;
+                System.Threading.Thread.Sleep(25);
+            }
+            // Tiny additional settle for the OS keyboard-focus IPC to finish
+            // after the foreground transition is observed.
+            System.Threading.Thread.Sleep(100);
         }
         catch
         {