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diff --git a/meshmc/launcher/updater/UpdateChecker.h b/meshmc/launcher/updater/UpdateChecker.h
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+/* SPDX-FileCopyrightText: 2026 Project Tick
+ * SPDX-FileContributor: Project Tick
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ *   MeshMC - A Custom Launcher for Minecraft
+ *   Copyright (C) 2026 Project Tick
+ *
+ *   This program is free software: you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation, either version 3 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <QObject>
+#include <QString>
+#include "net/NetJob.h"
+
+/*!
+ * Carries all information about an available update that is needed by the
+ * UpdateController and the UpdateDialog.
+ */
+struct UpdateAvailableStatus {
+	/// Normalized version string, e.g. "7.1.0"
+	QString version;
+	/// Direct download URL for this platform's artifact (from the feed).
+	QString downloadUrl;
+	/// HTML release notes extracted from the feed's <description> element.
+	QString releaseNotes;
+};
+Q_DECLARE_METATYPE(UpdateAvailableStatus)
+
+/*!
+ * UpdateChecker performs the two-source update check used by MeshMC.
+ *
+ * Algorithm:
+ *   1. Download the RSS feed at BuildConfig.UPDATER_FEED_URL in parallel with
+ *      the GitHub releases JSON at BuildConfig.UPDATER_GITHUB_API_URL.
+ *   2. Parse the latest stable <item> from the feed → extract <projt:version>
+ *      and the <projt:asset> URL whose name contains
+ * BuildConfig.BUILD_ARTIFACT.
+ *   3. Parse the GitHub JSON → strip leading "v" from tag_name.
+ *   4. Both versions must match and be greater than the running version;
+ *      otherwise the check is considered a no-update or failure.
+ *
+ * Platform / mode gating (runtime):
+ *   - Linux + APPIMAGE env variable set  → updater disabled.
+ *   - Linux + no portable.txt in app dir → updater disabled.
+ *   - Windows / macOS / Linux-portable   → updater active.
+ */
+class UpdateChecker : public QObject
+{
+	Q_OBJECT
+
+  public:
+	explicit UpdateChecker(shared_qobject_ptr<QNetworkAccessManager> nam,
+						   QObject* parent = nullptr);
+
+	/*!
+	 * Starts an asynchronous two-source update check.
+	 * If \a notifyNoUpdate is true, noUpdateFound() is emitted when the running
+	 * version is already the latest; otherwise the signal is suppressed.
+	 * Repeated calls while a check is in progress are silently ignored.
+	 */
+	void checkForUpdate(bool notifyNoUpdate);
+
+	/*!
+	 * Returns true if the updater may run on this platform / installation mode.
+	 * Evaluated at runtime: AppImage detection, portable.txt presence, OS.
+	 * Also checks that BuildConfig.UPDATER_ENABLED is true.
+	 */
+	static bool isUpdaterSupported();
+
+  signals:
+	//! Emitted when both sources agree that a newer version is available.
+	void updateAvailable(UpdateAvailableStatus status);
+
+	//! Emitted when the check completes but the running version is current.
+	void noUpdateFound();
+
+	//! Emitted on any network or parse failure.
+	void checkFailed(QString reason);
+
+  private slots:
+	void onDownloadsFinished(bool notifyNoUpdate);
+	void onDownloadsFailed(QString reason);
+
+  private:
+	static bool isPortableMode();
+	static bool isAppImage();
+	/// Returns current version as "MAJOR.MINOR.HOTFIX".
+	static QString currentVersion();
+	/// Strips a leading 'v' and returns a clean X.Y.Z string.
+	static QString normalizeVersion(const QString& v);
+	/// Compares two "X.Y.Z" strings numerically. Returns >0 if v1 > v2.
+	static int compareVersions(const QString& v1, const QString& v2);
+
+	shared_qobject_ptr<QNetworkAccessManager> m_network;
+	NetJob::Ptr m_checkJob;
+	QByteArray m_feedData;
+	QByteArray m_githubData;
+	bool m_checking = false;
+};