Fix QML performance and stability issues

- Fix TypeError by using explicit id instead of parent.parent chains
- Remove onContentHeightChanged handler that caused layout thrashing
- Add active guard on Loader to prevent null modelData access
- Simplify blockSegments null checks

gui/main.qml

@@ -1265,13 +1265,6 @@ ApplicationWindow {
                             }
                         }
                         
-                        onContentHeightChanged: {
-                            // Content height changed (e.g., after loading) - scroll if following
-                            if (shouldAutoScroll && count > 0) {
-                                positionViewAtEnd()
-                            }
-                        }
-
                         onCountChanged: {
                             // New block added - always scroll if we were following
                             if (count > 0) {
@@ -1393,10 +1386,11 @@ property bool blockExpanded: {
                 model: blockSegments || []
                 
                 delegate: Loader {
-                    width: parent.width
+                    width: parent ? parent.width : 0
-                    sourceComponent: modelData.type === "diagram" ? diagramComponent : textComponent
+                    active: modelData !== null && modelData !== undefined
+                    sourceComponent: (modelData && modelData.type === "diagram") ? diagramComponent : textComponent
                     
-                    property var segmentData: modelData
+                    property var segmentData: modelData || {}
                 }
             }
         }
@@ -1406,6 +1400,7 @@ property bool blockExpanded: {
             id: textComponent
             
             TextEdit {
+                id: textSegmentEdit
                 width: parent ? parent.width : 100
                 text: segmentData.html || ""
                 textFormat: Text.RichText
@@ -1427,12 +1422,12 @@ property bool blockExpanded: {
                     id: textSegmentMenu
                     MenuItem {
                         text: "Copy"
-                        enabled: parent.parent.selectedText.length > 0
+                        enabled: textSegmentEdit.selectedText.length > 0
-                        onTriggered: parent.parent.copy()
+                        onTriggered: textSegmentEdit.copy()
                     }
                     MenuItem {
                         text: "Select All"
-                        onTriggered: parent.parent.selectAll()
+                        onTriggered: textSegmentEdit.selectAll()
                     }
                 }