Fix MCP use-after-free, scanner chunk overlap, build scripts

- MCP bridge: guard against use-after-free when client disconnects
  during sendJson flush by re-checking m_client after write
- Scanner engine: fix chunk overlap advancing past region end on
  final chunk; fix fallback region flags for providers without
  enumerateRegions
- Build scripts: prefer GCC MinGW over LLVM-MinGW in PATH detection

src/mcp/mcp_bridge.cpp

@@ -45,9 +45,13 @@ void McpBridge::start() {
 
 void McpBridge::stop() {
     if (m_client) {
+        m_client->disconnect(this);
         m_client->disconnectFromServer();
+        m_client->deleteLater();
         m_client = nullptr;
     }
+    m_readBuffer.clear();
+    m_initialized = false;
     if (m_server) {
         m_server->close();
         delete m_server;
@@ -65,8 +69,10 @@ void McpBridge::onNewConnection() {
 
     // Single client — disconnect previous
     if (m_client) {
+        m_client->disconnect(this);
         m_client->disconnectFromServer();
         m_client->deleteLater();
+        m_client = nullptr;
     }
 
     m_client = pending;
@@ -82,10 +88,13 @@ void McpBridge::onNewConnection() {
 }
 
 void McpBridge::onReadyRead() {
+    if (!m_client) return;
     m_readBuffer.append(m_client->readAll());
 
     // Newline-delimited JSON framing
-    while (true) {
+    // Guard: processLine→sendJson→flush can re-enter the event loop
+    // and trigger onDisconnected, nulling m_client mid-loop.
+    while (m_client) {
         int idx = m_readBuffer.indexOf('\n');
         if (idx < 0) break;
         QByteArray line = m_readBuffer.left(idx).trimmed();
@@ -97,7 +106,12 @@ void McpBridge::onReadyRead() {
 
 void McpBridge::onDisconnected() {
     qDebug() << "[MCP] Client disconnected";
-    m_client = nullptr;
+    if (m_client) {
+        m_client->disconnect(this);
+        m_client->deleteLater();
+        m_client = nullptr;
+    }
+    m_readBuffer.clear();
     m_initialized = false;
 }
 
@@ -127,7 +141,7 @@ void McpBridge::sendJson(const QJsonObject& obj) {
     qDebug() << "[MCP] >>" << data.left(200);
     data.append('\n');
     m_client->write(data);
-    m_client->flush();
+    if (m_client) m_client->flush();
 }
 
 void McpBridge::sendNotification(const QString& method, const QJsonObject& params) {
@@ -172,12 +186,10 @@ void McpBridge::processLine(const QByteArray& line) {
 
     if (method == "initialize") {
         m_mainWindow->setMcpStatus(QStringLiteral("MCP: client connected"));
-        QCoreApplication::processEvents();
         sendJson(handleInitialize(id, req.value("params").toObject()));
         m_mainWindow->clearMcpStatus();
     } else if (method == "tools/list") {
         m_mainWindow->setMcpStatus(QStringLiteral("MCP: tools/list"));
-        QCoreApplication::processEvents();
         sendJson(handleToolsList(id));
         m_mainWindow->clearMcpStatus();
     } else if (method == "tools/call") {

src/scanner.cpp

@@ -473,14 +473,14 @@ QVector<ScanResult> ScanEngine::runScan(std::shared_ptr<Provider> prov,
              << " filterExec:" << req.filterExecutable
              << " filterWrite:" << req.filterWritable;
 
-    // Fallback for providers that don't enumerate regions (file/buffer)
+    // Fallback for providers that don't enumerate regions (file/buffer/syscall without modules)
     if (regions.isEmpty()) {
         MemoryRegion fallback;
         fallback.base = 0;
         fallback.size = (uint64_t)prov->size();
         fallback.readable = true;
         fallback.writable = true;
-        fallback.executable = false;
+        fallback.executable = true;  // unknown; include so filters don't exclude the only region
         regions.append(fallback);
     }
 
@@ -515,7 +515,8 @@ QVector<ScanResult> ScanEngine::runScan(std::shared_ptr<Provider> prov,
 
     constexpr int kChunk = 256 * 1024;
 
-    for (const auto& region : regions) {
+    for (int regionIndex = 0; regionIndex < regions.size(); ++regionIndex) {
+        const auto& region = regions[regionIndex];
         if (m_abort.load()) break;
 
         if (req.filterExecutable && !region.executable) continue;
@@ -540,7 +541,7 @@ QVector<ScanResult> ScanEngine::runScan(std::shared_ptr<Provider> prov,
             continue;
         }
 
-        const int overlap = patternLen - 1;
+        const int overlap = patternLen;  // need full patternLen overlap so pattern at chunk end is found
         QByteArray chunk(qMin((uint64_t)kChunk, regSize), Qt::Uninitialized);
         uint64_t regOffset = regStart - region.base; // offset within provider region
 
@@ -552,6 +553,8 @@ QVector<ScanResult> ScanEngine::runScan(std::shared_ptr<Provider> prov,
 
             if (!prov->read(regStart + off, chunk.data(), readLen)) {
                 // Skip unreadable chunk
+                qDebug() << "[scan] read failed region" << regionIndex << "addr" << Qt::showbase << Qt::hex
+                         << (region.base + off) << "base" << region.base << "off" << off << "len" << readLen << Qt::dec;
                 off += readLen;
                 scannedBytes += readLen;
                 continue;