gui: fix freeze on agent switch — bulk load chat blocks

appendContent was calling rebuildBlockHtml (full syntax highlighting)
on every single line during initial log load. For a 1000-line chat,
that's O(n²) highlighting passes.

Add beginBulkLoad()/endBulkLoad() — skips per-line rebuilds during
bulk, then rebuilds all blocks once at the end. QML load sites now
wrap appendData(log) with bulk mode.

gui/chatblockmodel.cpp

@@ -480,10 +480,29 @@ void ChatBlockModel::appendContent(const QString &line)
         last.content += '\n';
     last.content += line;
 
-    rebuildBlockHtml(m_blocks.size() - 1);
+    if (!m_bulkLoading) {
+        rebuildBlockHtml(m_blocks.size() - 1);
+        QModelIndex idx = index(m_blocks.size() - 1);
+        emit dataChanged(idx, idx, {ContentRole, RenderedHtmlRole, SegmentsRole});
+    }
+}
 
-    QModelIndex idx = index(m_blocks.size() - 1);
+void ChatBlockModel::beginBulkLoad()
-    emit dataChanged(idx, idx, {ContentRole, RenderedHtmlRole, SegmentsRole});
+{
+    m_bulkLoading = true;
+}
+
+void ChatBlockModel::endBulkLoad()
+{
+    m_bulkLoading = false;
+    // Rebuild HTML for all blocks once.
+    for (int i = 0; i < m_blocks.size(); ++i) {
+        rebuildBlockHtml(i);
+    }
+    if (!m_blocks.isEmpty()) {
+        emit dataChanged(index(0), index(m_blocks.size() - 1),
+                         {ContentRole, RenderedHtmlRole, SegmentsRole});
+    }
 }
 
 void ChatBlockModel::processLine(const QString &line)

gui/chatblockmodel.h

@@ -78,6 +78,8 @@ public:
     QHash<int, QByteArray> roleNames() const override;
 
     Q_INVOKABLE void appendData(const QString &text);
+    Q_INVOKABLE void beginBulkLoad();
+    Q_INVOKABLE void endBulkLoad();
     Q_INVOKABLE void reset();
     Q_INVOKABLE void trimFront(int keepCount);
     Q_INVOKABLE void clearDiagramCache();
@@ -110,6 +112,7 @@ private:
     QVariantList segmentsToVariant(const QList<BlockSegment> &segments) const;
 
     State m_state = State::BlockStart;
+    bool m_bulkLoading = false;
     KSyntaxHighlighting::Repository *m_repo = nullptr;
     QNetworkAccessManager *m_netManager = nullptr;
 

gui/main.qml

@@ -463,8 +463,10 @@ ApplicationWindow {
         if (ollie.activeAgentId) {
             var log = ollie.readLogForSession(ollie.activeSessionId, ollie.activeAgentId)
             if (log) {
+                chatModel.beginBulkLoad()
                 chatModel.appendData(log)
                 chatModel.trimFront(20)
+                chatModel.endBulkLoad()
             }
         }
         ollie.refreshSessions()
@@ -479,8 +481,10 @@ ApplicationWindow {
             if (ollie.activeSessionId && ollie.activeAgentId) {
                 var log = ollie.readLogForSession(ollie.activeSessionId, ollie.activeAgentId)
                 if (log) {
+                    chatModel.beginBulkLoad()
                     chatModel.appendData(log)
                     chatModel.trimFront(20)
+                    chatModel.endBulkLoad()
                 }
             }
         }
@@ -490,8 +494,10 @@ ApplicationWindow {
             if (ollie.activeSessionId && ollie.activeAgentId) {
                 var log = ollie.readLogForSession(ollie.activeSessionId, ollie.activeAgentId)
                 if (log) {
+                    chatModel.beginBulkLoad()
                     chatModel.appendData(log)
                     chatModel.trimFront(20)
+                    chatModel.endBulkLoad()
                 }
             }
         }