fix: merge two strokecanvas into one + better cursorShape and pointer handling

Plugins/ZShell/Internal/strokecanvasrenderer.cpp

@@ -1,6 +1,7 @@
 #include "strokecanvasrenderer.hpp"
 #include "strokecanvasitem.hpp"
 #include <qcolor.h>
+#include <QSet>
 
 namespace ZShell::internal {
 
@@ -148,14 +149,27 @@ void StrokeCanvasRenderer::synchronizeData(QCanvasPainterItem* item) {
 	m_penColor = canvas->m_penColor;
 	m_penWidth = canvas->m_penWidth;
 
-	while (m_strokes.size() < canvas->m_strokes.size())
-		m_strokes.append(canvas->m_strokes[m_strokes.size()]);
+	// Detect removed strokes: present in renderer but no longer in canvas
+	QSet<int> canvasGroupIds;
+	for (const auto& stroke : canvas->m_strokes)
+		canvasGroupIds.insert(stroke.groupId);
 
-	if (canvas->m_strokes.isEmpty() && !m_strokes.isEmpty()) {
-		for (const auto& stroke : m_strokes)
-			if (stroke.groupId >= 0)
-				m_pendingGroupRemovals.append(stroke.groupId);
-		m_strokes.clear();
+	for (int i = m_strokes.size() - 1; i >= 0; --i) {
+		if (!canvasGroupIds.contains(m_strokes[i].groupId)) {
+			if (m_strokes[i].groupId >= 0)
+				m_pendingGroupRemovals.append(m_strokes[i].groupId);
+			m_strokes.remove(i);
+		}
+	}
+
+	// Detect added strokes: present in canvas but not yet in renderer
+	QSet<int> rendererGroupIds;
+	for (const auto& stroke : m_strokes)
+		rendererGroupIds.insert(stroke.groupId);
+
+	for (const auto& stroke : canvas->m_strokes) {
+		if (!rendererGroupIds.contains(stroke.groupId))
+			m_strokes.append(stroke);
 	}
 
 	m_currentStroke = canvas->m_currentStroke;