refactor: Decoupling chat architecture (#367)

* refactor: Migrate tests to Qt Creator plugin framework and update llmqore transports

* refactor: Move conversation history into IDE-free session library

* refactor: Extract turn context assembly behind injected ports

* build: Add RunQodeAssistTests target for the plugin test suite

* refactor: Route the chat through a Session and ChatBackend seam

sources/session/FileEditPayload.cpp

@@ -0,0 +1,49 @@
+// Copyright (C) 2026 Petr Mironychev
+// SPDX-License-Identifier: GPL-3.0-or-later
+// Additional attribution terms under GPLv3 §7(b) apply — see LICENSE
+
+#include "session/FileEditPayload.hpp"
+
+#include <QJsonDocument>
+
+namespace QodeAssist::Session {
+
+namespace {
+
+QString fileEditMarker()
+{
+    return QStringLiteral("QODEASSIST_FILE_EDIT:");
+}
+
+} // namespace
+
+bool isFileEditPayload(const QString &text)
+{
+    return text.startsWith(fileEditMarker());
+}
+
+std::optional<QJsonObject> parseFileEditPayload(const QString &text)
+{
+    const QString marker = fileEditMarker();
+    const int markerPos = text.indexOf(marker);
+    if (markerPos < 0)
+        return std::nullopt;
+
+    const int jsonStart = markerPos + marker.length();
+    if (jsonStart >= text.length())
+        return std::nullopt;
+
+    const QJsonDocument document = QJsonDocument::fromJson(text.mid(jsonStart).toUtf8());
+    if (!document.isObject())
+        return std::nullopt;
+
+    return document.object();
+}
+
+QString encodeFileEditPayload(const QJsonObject &payload)
+{
+    return fileEditMarker()
+           + QString::fromUtf8(QJsonDocument(payload).toJson(QJsonDocument::Compact));
+}
+
+} // namespace QodeAssist::Session