feat: add support acp in common chat (#369)

sources/session/AgentPlan.cpp

@@ -0,0 +1,57 @@
+// 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/AgentPlan.hpp"
+
+#include <QJsonArray>
+
+#include "session/BlockCodec.hpp"
+
+namespace QodeAssist::Session {
+
+QJsonObject planBlockToJson(const PlanBlock &block)
+{
+    QJsonArray entries;
+    for (const PlanEntry &entry : block.entries) {
+        QJsonObject json{{"content", entry.content}, {"status", entry.status}};
+        if (!entry.priority.isEmpty())
+            json["priority"] = entry.priority;
+        entries.append(json);
+    }
+
+    return QJsonObject{{"entries", entries}};
+}
+
+PlanBlock planBlockFromJson(const QJsonObject &json)
+{
+    PlanBlock block;
+
+    const QJsonArray entries = json["entries"].toArray();
+    for (const QJsonValue &value : entries) {
+        const QJsonObject entry = value.toObject();
+        block.entries.append(
+            PlanEntry{
+                entry["content"].toString(),
+                entry["priority"].toString(),
+                entry["status"].toString()});
+    }
+
+    return block;
+}
+
+QString encodePlanBlock(const PlanBlock &block)
+{
+    return encodeMarkerPayload(planPayloadMarker, planBlockToJson(block));
+}
+
+std::optional<PlanBlock> decodePlanBlock(const QString &text)
+{
+    const auto payload = decodeMarkerPayload(planPayloadMarker, text);
+    if (!payload)
+        return std::nullopt;
+
+    return planBlockFromJson(*payload);
+}
+
+} // namespace QodeAssist::Session