Deliver each drop to the zone under the cursor (#953)

app/MindWork AI Studio/Tools/Rust/DropPosition.cs

@@ -0,0 +1,13 @@
+namespace AIStudio.Tools.Rust;
+
+/// <summary>
+/// The cursor position of a drag and drop event.
+/// </summary>
+/// <remarks>
+/// The coordinates are viewport-relative CSS pixels, on every platform. The Rust runtime has already
+/// dealt with the platform differences -- device pixels on Windows, logical points on macOS and Linux --
+/// so these numbers can be handed to the browser for a hit test without any further conversion.
+/// </remarks>
+/// <param name="X">The distance from the left edge of the viewport, in CSS pixels.</param>
+/// <param name="Y">The distance from the top edge of the viewport, in CSS pixels.</param>
+public readonly record struct DropPosition(double X, double Y);

app/MindWork AI Studio/Tools/Rust/TauriEvent.cs

@@ -5,7 +5,8 @@ namespace AIStudio.Tools.Rust;
 /// </summary>
 /// <param name="EventType">The type of the Tauri event.</param>
 /// <param name="Payload">The payload of the Tauri event.</param>
-public readonly record struct TauriEvent(TauriEventType EventType, List<string> Payload)
+/// <param name="Position">Where the cursor was, for the drag and drop events which know it.</param>
+public readonly record struct TauriEvent(TauriEventType EventType, List<string> Payload, DropPosition? Position = null)
 {
     /// <summary>
     /// Attempts to parse the first payload element as a shortcut.
@@ -29,6 +30,28 @@ public readonly record struct TauriEvent(TauriEventType EventType, List<string>
         return TryParseSnakeCase(this.Payload[0], out shortcut);
     }
 
+    /// <summary>
+    /// Reads the cursor position of a drag and drop event.
+    /// </summary>
+    /// <remarks>
+    /// The coordinates are viewport-relative CSS pixels, ready for a hit test in the browser. Only the
+    /// drag and drop events carry them, which is why the caller has to ask instead of assuming.
+    /// </remarks>
+    /// <param name="x">The distance from the left edge of the viewport, in CSS pixels.</param>
+    /// <param name="y">The distance from the top edge of the viewport, in CSS pixels.</param>
+    /// <returns>True if the event carried a position, false otherwise.</returns>
+    public bool TryGetDropPosition(out double x, out double y)
+    {
+        x = 0.0;
+        y = 0.0;
+        if (this.Position is not { } position)
+            return false;
+
+        x = position.X;
+        y = position.Y;
+        return true;
+    }
+
     /// <summary>
     /// Reads a portal shortcut change and its effective display name.
     /// </summary>

app/MindWork AI Studio/Tools/Rust/TauriEventType.cs

@@ -13,6 +13,7 @@ public enum TauriEventType
     WINDOW_NOT_FOCUSED,
 
     FILE_DROP_HOVERED,
+    FILE_DROP_OVER,
     FILE_DROP_DROPPED,
     FILE_DROP_CANCELED,