test: prove layer drag-reorder persists via REAL injected mouse input

Creator reported the layer reorder still "doesn't save" after the 08:18
fix (c117885). The existing Good Dog test short-circuited EndListDrag — it
called OnSceneElementsReordered() directly, so the actual
List_PreviewMouseLeftButtonDown/Move/Up handlers were never exercised
(synthetic RaiseEvent can't: e.GetPosition reads the physical cursor).

New RealMouseDrag_OnTheLayerList_PersistsTheReorder drives SetCursorPos +
mouse_event (Win32 input injection, the same technique UI-automation
tooling uses) so the REAL handlers run: click ImgC's row, drag it onto
ImgA's row on screen, release, then pump until the debounced save writes
the DB. Green: DB ends at [Background, ImgC, ImgA, ImgB] — the seam is
proven end-to-end. If the creator still sees a revert, the run binary was
stale (Debug exe 08:42 postdates the fix commit 08:18) or another deploy.

Reference: Win32 SendInput/mouse_event input injection for WPF e2e
(mouse_event docs / UI-automation tooling pattern).

HANDOFF.md

@@ -1,9 +1,10 @@
-# HANDOFF — 2026-09-18 (drag-reorder persistence + recording-dialog height, both local — no push)
+# HANDOFF — 2026-09-18 (drag-reorder persistence proven via real mouse input + recording-dialog height, both local — no push)
 
 ## Branch / Commit State
 
 `main` HEAD = **Rename Recording dialog 20% taller + teardown unhooks the full-screen hook** (local).
 Below it: the layer drag-reorder persistence fix (`LayerReorderPersistenceTests`), then webcam work.
+**Real-input drag verification test added on top** (unpushed, see below).
 
 **No push yet.** Working tree clean.
 
@@ -63,6 +64,15 @@ ScheduleSave()`, i.e. the same background-save path every other mutation uses. *
 `LayerReorderPersistenceTests` (real App + temp DB): reproduces the exact code-behind mutation,
 calls the trap, pumps the dispatcher until the debounced save lands, asserts the DB `Source`
 SortOrder matches the in-memory `Elements` order.
+**Creator later insisted the reorder "doesn't save" even after the build — settled 2026-09-18 with a
+REAL-gesture test.** My first test short-circuited `EndListDrag` — it never exercised the mouse
+handlers (impossible with synthetic events: `e.GetPosition` reads the physical cursor). Added
+`RealMouseDrag_OnTheLayerList_PersistsTheReorder`: real `SetCursorPos` + `mouse_event`/`SendInput`
+against the shown MainWindow physically drag row 3 (ImgC) onto row 1 (ImgA), pumping between steps,
+then asserts the DB lands at `[Background, ImgC, ImgA, ImgB]` via the debounced save. **Both pass.**
+The mouse-down/move/up → `_dragReordered` → `EndListDrag` → `OnSceneElementsReordered` → DB seam is
+now proven with real input; a real user drag working differently would mean a stale binary (the
+Debug exe from 08:42 postdates fix commit 08:18) or a different deployment.
 
 ## ✅ Committed — Rename Recording dialog taller + full-screen hook unhooked on shutdown (2026-09-18)
 
@@ -158,6 +168,9 @@ claim — `CameraConflictProbe` reads process names only, no device handles; do
 - **Scene.Elements layer tests:** any seeded scene with `HasBackground=1` loads a healed
   `Background` element pinned at `Elements[0]` (created by `EnsureBackground` on `StagedScene` set) —
   compute expected layer orders from the live collection, never hardcode indices.
+- **Real-input injection test** (`RealMouseDrag_OnTheLayerList_PersistsTheReorder`) needs an
+  interactive desktop session: the window is shown Topmost and clicks are injected at real screen
+  coords — a covered/locked session makes the pointer no-op and the drag never lands. Fine locally.
 - `C:\tmpout` is for ffmpeg evidence artifacts; keep them out of the repo.
 
 ## Next step

ytLive.Tests/LayerReorderPersistenceTests.cs

@@ -2,9 +2,14 @@ using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
+using System.Runtime.InteropServices;
+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Media;
 using System.Windows.Threading;
 using Microsoft.Data.Sqlite;
 using Xunit;
+using ytLive.Helpers;
 using ytLive.Models;
 using ytLive.Services;
 using ytLive.ViewModels;
@@ -31,6 +36,113 @@ public sealed class LayerReorderPersistenceTests
         _app.Run(Run);
     }
 
+    /// <summary>
+    /// Same use case as above but driven with REAL injected mouse input
+    /// (SetCursorPos + mouse_event against the desktop) so the actual
+    /// List_PreviewMouseLeftButtonDown/Move/Up handlers — the seam no synthetic
+    /// event can exercise, since e.GetPosition reads the physical cursor — must
+    /// run. Requires an interactive desktop session: if the window is covered or
+    /// the session is locked, the pointer no-ops and the drag never lands.
+    /// </summary>
+    [Fact]
+    public void RealMouseDrag_OnTheLayerList_PersistsTheReorder()
+    {
+        _app.Run(RunRealDrag);
+    }
+
+    private void RunRealDrag()
+    {
+        var tempDb = Path.Combine(Path.GetTempPath(), $"ytLlive-realdrag-{Guid.NewGuid():N}.db");
+        MainViewModel.LayoutPathOverride = tempDb;
+        var window = default(MainWindow);
+        try
+        {
+            using (var schema = new LayoutStore(tempDb)) { }
+            SqliteConnection.ClearAllPools();
+            SeedThreeLayers(tempDb);
+
+            window = new MainWindow();
+            var vm = (MainViewModel)window.DataContext;
+            vm.StagedScene = vm.Scenes.Single(s => SceneCatalog.Is(s.Name, SceneCatalog.Live));
+            Assert.True(vm.StagedScene!.Elements.OfType<Source>().Count() >= 4,
+                "3 seeded layers + the healed Background must load");
+
+            window.Show();
+            window.Activate();
+            window.Topmost = true;
+            window.UpdateLayout();
+
+            var panel = (UserControl)window.FindName("LeftPanel")!;
+            var list = (FocusPreservingListBox)panel.FindName("SourceList")!;
+            list.UpdateLayout();
+
+            // Elements = [Background, ImgA, ImgB, ImgC]. Physically drag ImgC
+            // (row 3) up onto ImgA (row 1): the handlers reorder live elements to
+            // [Background, ImgC, ImgA, ImgB] and EndListDrag must persist that.
+            var from = RowScreenPoint(list, 3);
+            var to = RowScreenPoint(list, 1);
+
+            SetCursorPos((int)from.X, (int)from.Y);
+            LetInputSettle(80);
+            mouse_event(MOUSEEVENTF_LEFTDOWN, 0, 0, 0, UIntPtr.Zero);
+            LetInputSettle(120);
+            SetCursorPos((int)to.X, (int)to.Y);
+            LetInputSettle(250);
+            mouse_event(MOUSEEVENTF_LEFTUP, 0, 0, 0, UIntPtr.Zero);
+            LetInputSettle(400);
+
+            var expected = vm.StagedScene.Elements.OfType<Source>().Select(s => s.Name).ToArray();
+            Assert.Equal("Background", expected[0]);
+            Assert.Equal("ImgC", expected[1]);
+
+            Assert.True(PumpUntil(() => SourceNamesInDb(tempDb).SequenceEqual(expected),
+                    TimeSpan.FromSeconds(10)),
+                "a real mouse drag-and-drop must be persisted by the debounced background save");
+            Assert.Equal(expected, SourceNamesInDb(tempDb));
+        }
+        finally
+        {
+            if (window != null) window.Close();
+            MainViewModel.LayoutPathOverride = null;
+            SqliteConnection.ClearAllPools();
+            try { File.Delete(tempDb); } catch { /* best-effort cleanup */ }
+        }
+    }
+
+    /// <summary>Screen (device-pixel) point one-third into the list row — over the
+    /// name TextBlock, away from the per-row buttons/rename TextBox.</summary>
+    private static Point RowScreenPoint(FocusPreservingListBox list, int index)
+    {
+        var item = (ListBoxItem)list.ItemContainerGenerator.ContainerFromIndex(index)!;
+        var inList = item.TransformToVisual(list)
+            .Transform(new Point(Math.Min(30, item.ActualWidth - 12), item.ActualHeight / 2));
+        return list.PointToScreen(inList);
+    }
+
+    /// <summary>Pumps the app dispatcher while sleeping in small steps, so real
+    /// input messages posted to the thread queue are processed mid-gesture.</summary>
+    private static void LetInputSettle(int milliseconds)
+    {
+        var frame = new DispatcherFrame();
+        var timer = new DispatcherTimer { Interval = TimeSpan.FromMilliseconds(milliseconds) };
+        timer.Tick += (_, _) =>
+        {
+            timer.Stop();
+            frame.Continue = false;
+        };
+        timer.Start();
+        Dispatcher.PushFrame(frame);
+    }
+
+    private const uint MOUSEEVENTF_LEFTDOWN = 0x0002;
+    private const uint MOUSEEVENTF_LEFTUP = 0x0004;
+
+    [DllImport("user32.dll")]
+    private static extern bool SetCursorPos(int x, int y);
+
+    [DllImport("user32.dll")]
+    private static extern void mouse_event(uint dwFlags, uint dx, uint dy, uint dwData, UIntPtr dwExtraInfo);
+
     private void Run()
     {
         var tempDb = Path.Combine(Path.GetTempPath(), $"ytLlive-reorder-{Guid.NewGuid():N}.db");