Add throttled breadcrumbs for drag-handle hit-test anomalies (#527)

Sources/WindowDragHandleView.swift

@@ -6,6 +6,55 @@ private func windowDragHandleFormatPoint(_ point: NSPoint) -> String {
     String(format: "(%.1f,%.1f)", point.x, point.y)
 }
 
+private func windowDragHandleEventTypeDescription(_ eventType: NSEvent.EventType?) -> String {
+    eventType.map { String(describing: $0) } ?? "nil"
+}
+
+private enum WindowDragHandleBreadcrumbLimiter {
+    private static var lastEmissionByKey: [String: CFAbsoluteTime] = [:]
+
+    static func shouldEmit(key: String, minInterval: CFTimeInterval) -> Bool {
+        let now = CFAbsoluteTimeGetCurrent()
+        if let previous = lastEmissionByKey[key], (now - previous) < minInterval {
+            return false
+        }
+        lastEmissionByKey[key] = now
+        if lastEmissionByKey.count > 128 {
+            let staleThreshold = now - max(minInterval * 4, 60)
+            lastEmissionByKey = lastEmissionByKey.filter { _, timestamp in
+                timestamp >= staleThreshold
+            }
+        }
+        return true
+    }
+}
+
+private func windowDragHandleEmitBreadcrumb(
+    _ message: String,
+    window: NSWindow?,
+    eventType: NSEvent.EventType?,
+    point: NSPoint,
+    minInterval: CFTimeInterval = 10,
+    extraData: [String: Any] = [:]
+) {
+    let windowNumber = window?.windowNumber ?? -1
+    let key = "\(message):\(windowNumber)"
+    guard WindowDragHandleBreadcrumbLimiter.shouldEmit(key: key, minInterval: minInterval) else {
+        return
+    }
+
+    var data: [String: Any] = [
+        "event_type": windowDragHandleEventTypeDescription(eventType),
+        "point": windowDragHandleFormatPoint(point),
+        "window_number": windowNumber,
+        "window_present": window != nil
+    ]
+    for (name, value) in extraData {
+        data[name] = value
+    }
+    sentryBreadcrumb(message, category: "titlebar.drag", data: data)
+}
+
 private func windowDragHandleShouldDeferHitCapture(for eventType: NSEvent.EventType?) -> Bool {
     switch eventType {
     case .leftMouseDown?:
@@ -171,6 +220,16 @@ func windowDragHandleShouldCaptureHit(
         // We only keep suppression active while the left mouse button is down.
         if (NSEvent.pressedMouseButtons & 0x1) == 0 {
             let clearedDepth = clearWindowDragSuppression(window: dragHandleView.window)
+            windowDragHandleEmitBreadcrumb(
+                "titlebar.dragHandle.suppression.recovered",
+                window: dragHandleView.window,
+                eventType: eventType,
+                point: point,
+                minInterval: 20,
+                extraData: [
+                    "cleared_depth": clearedDepth
+                ]
+            )
             #if DEBUG
             dlog(
                 "titlebar.dragHandle.hitTest suppressionRecovered clearedDepth=\(clearedDepth) point=\(windowDragHandleFormatPoint(point))"
@@ -239,6 +298,17 @@ func windowDragHandleShouldCaptureHit(
                 "titlebar.dragHandle.hitTest capture=false point=\(windowDragHandleFormatPoint(point)) siblingCount=\(siblingCount) sibling=\(type(of: sibling)) hit=\(type(of: hitView)) passiveHost=false"
             )
             #endif
+            windowDragHandleEmitBreadcrumb(
+                "titlebar.dragHandle.hitTest.blockedBySiblingHit",
+                window: dragHandleView.window,
+                eventType: eventType,
+                point: point,
+                minInterval: 8,
+                extraData: [
+                    "sibling_type": String(describing: type(of: sibling)),
+                    "hit_type": String(describing: type(of: hitView))
+                ]
+            )
             return false
         }
     }