chat log: switch to [[[type]]]/[[[end]]] block format

Replace the single-bracket INI-like format with triple-bracket blocks
with explicit [[[end]]] terminators. The parser tracks m_inBlock to
ignore content between blocks, making the format robust against
accidental header-like content in tool output or LLM responses.

- Go sender: FormatEvent + NewEventHandler + replayMessagesToLog
- C++ parser: new regex for [[[type]]], new [[[end]]] handler, m_inBlock gate
- QML: update hardcoded [info] string

gui/chatblockmodel.cpp

@@ -44,7 +44,10 @@ private:
 // --- Block Parsing ---
 
 const QRegularExpression ChatBlockModel::s_headerRe(
-    R"(^\[(user|assistant|reasoning|call|tool|error|info|retry)(?::([^\]]*))?\]$)");
+    R"(^\[\[\[(user|assistant|reasoning|call|tool|error|info|retry)(?::([^\]]*))?\]\]\]$)");
+
+const QRegularExpression ChatBlockModel::s_endRe(
+    R"(^\[\[\[end\]\]\]$)");
 
 ChatBlockModel::ChatBlockModel(QObject *parent)
     : QAbstractListModel(parent)
@@ -118,6 +121,7 @@ void ChatBlockModel::reset()
     m_fenceState = NoFence;
     m_fenceLang.clear();
     m_fenceBuffer.clear();
+    m_inBlock = false;
     endResetModel();
     emit countChanged();
 }
@@ -225,6 +229,12 @@ void ChatBlockModel::processLine(const QString &line)
         return;
     }
 
+    // --- End block marker ---
+    if (s_endRe.match(line).hasMatch()) {
+        m_inBlock = false;
+        return;
+    }
+
     // --- NoFence state: look for opening fence or header ---
     static const QRegularExpression fenceOpenRe(R"(^```(\w*)[ \t]*$)");
     QRegularExpressionMatch fenceMatch = fenceOpenRe.match(line);
@@ -265,16 +275,23 @@ void ChatBlockModel::processLine(const QString &line)
         m_blocks.append({type, qualifier, QString(), QString()});
         endInsertRows();
         emit countChanged();
+        m_inBlock = true;
         return;
     }
 
-    // Content line — append to the last block if any
-    if (m_blocks.isEmpty()) {
-        // Mid-stream connect: create a Default block
-        beginInsertRows(QModelIndex(), 0, 0);
-        m_blocks.append({ChatBlock::Default, QString(), QString(), QString()});
-        endInsertRows();
-        emit countChanged();
+    // Content line — only append if inside a block or connecting mid-stream
+    if (!m_inBlock) {
+        // Dropped content between blocks — ignore to avoid accidental parsing.
+        // Mid-stream connect: if no blocks exist yet, create a default container.
+        if (m_blocks.isEmpty()) {
+            beginInsertRows(QModelIndex(), 0, 0);
+            m_blocks.append({ChatBlock::Default, QString(), QString(), QString()});
+            endInsertRows();
+            emit countChanged();
+            m_inBlock = true;
+        } else {
+            return;
+        }
     }
 
     ChatBlock &last = m_blocks.last();

gui/chatblockmodel.h

@@ -60,6 +60,11 @@ private:
     QString m_fenceLang;
     QString m_fenceBuffer;
 
+    // Block state machine — tracks whether we're inside a [[[type]]]...[[[end]]] block.
+    // Content lines outside a block are ignored, making the format robust against
+    // accidental header-like content in the wild.
+    bool m_inBlock = false;
+
     // Syntax highlighting (shared with Kate plugin pattern)
     QString highlightCode(const QString &code, const QString &language) const;
     QString renderDiff(const QString &diff) const;
@@ -69,6 +74,7 @@ private:
     QString m_lineBuffer;
 
     static const QRegularExpression s_headerRe;
+    static const QRegularExpression s_endRe;
 };
 
 #endif // CHATBLOCKMODEL_H

gui/main.qml

@@ -207,7 +207,7 @@ ApplicationWindow {
             buildSessionTree()
         }
         function onStreamingDone() {
-            chatModel.appendData("\n[info]\nsession ended\n")
+            chatModel.appendData("\n[[[info]]]\nsession ended\n[[[end]]]\n")
         }
     }