Updater v1 --upgrade + roadmap as flat backlog

Updater: watch-together --upgrade checks updates/manifest.json,
downloads the tarball, verifies sha256, applies over the live
install (extract-temp + delete-first move-over; rename-safe on
Linux while running). Zero Flutter imports, 7 tests incl.
stub-server flows. Version stamped via --dart-define=APP_VERSION
in package script. Warns (never silently jumps) on proto mismatch.
Roadmap: phases retired as tracker (history in git log), now flat
Built/Backlog/Epics/Deferred; Jellyfin next feature, transcode
never; updater expansion stays an epic. Endpoint publishing
(manifest + release tarball) is user-owned.

apps/desktop/lib/src/update/updater.dart

@@ -0,0 +1,236 @@
+import 'dart:convert';
+import 'dart:io';
+
+import 'package:archive/archive.dart';
+import 'package:crypto/crypto.dart';
+import 'package:sync_relay_core/core.dart';
+
+// Zero Flutter imports: this file must stay unit-testable with plain
+// `flutter test` (no widgets, no media_kit). Linux-first v1: a CLI flag,
+// `watch-together --upgrade`, that checks the manifest, downloads the
+// tarball, verifies sha256, and extracts it over the live install.
+// Linux allows replacing (unlink/rename) files under a running process —
+// only opening the running binary for writing is refused (ETXTBSY) — so
+// apply is extract-to-temp then delete-first move-over, and the running
+// (old) image just prints the result and exits. Next launch is new.
+
+const updateManifestUrl =
+    'https://git.senkochan.moe/Foxyz/sync_replay_project/raw/branch/main/updates/manifest.json';
+
+const appVersion = String.fromEnvironment('APP_VERSION',
+    defaultValue: '0.0.0-dev');
+
+class UpdateManifest {
+  final String version;
+  final int protocol;
+  final String url;
+  final String sha256;
+  final String notes;
+  const UpdateManifest(
+      {required this.version,
+      required this.protocol,
+      required this.url,
+      required this.sha256,
+      required this.notes});
+
+  factory UpdateManifest.fromJson(Map<String, Object?> json) {
+    final version = json['version'];
+    final protocol = json['protocol'];
+    final url = json['url'];
+    final sha = json['sha256'];
+    if (version is! String ||
+        version.isEmpty ||
+        protocol is! int ||
+        url is! String ||
+        url.isEmpty ||
+        sha is! String ||
+        sha.isEmpty) {
+      throw const FormatException('update manifest missing version/protocol/url/sha256');
+    }
+    return UpdateManifest(
+        version: version,
+        protocol: protocol,
+        url: url,
+        sha256: sha,
+        notes: (json['notes'] as String?) ?? '');
+  }
+}
+
+List<int> parseVersion(String v) {
+  final out = <int>[];
+  for (final part in v.split('.')) {
+    final m = RegExp(r'\d+').firstMatch(part);
+    if (m == null) break;
+    out.add(int.parse(m.group(0)!));
+    if (out.length == 3) break;
+  }
+  while (out.length < 3) {
+    out.add(0);
+  }
+  return out;
+}
+
+bool isNewerVersion(String current, String latest) {
+  final c = parseVersion(current);
+  final l = parseVersion(latest);
+  for (var i = 0; i < 3; i++) {
+    if (l[i] != c[i]) return l[i] > c[i];
+  }
+  return false;
+}
+
+Future<UpdateManifest> fetchManifest(
+    {HttpClient? http, String url = updateManifestUrl}) async {
+  final client = http ?? HttpClient();
+  try {
+    final req = await client
+        .getUrl(Uri.parse(url))
+        .timeout(const Duration(seconds: 15));
+    final res = await req.close();
+    final body = await res.transform(utf8.decoder).join();
+    if (res.statusCode != 200) {
+      throw HttpException('manifest fetch failed: HTTP ${res.statusCode}');
+    }
+    final decoded = jsonDecode(body);
+    if (decoded is! Map<String, Object?>) {
+      throw const FormatException('manifest is not a JSON object');
+    }
+    return UpdateManifest.fromJson(decoded);
+  } finally {
+    client.close();
+  }
+}
+
+Future<void> downloadFile(String url, File dest, {HttpClient? http}) async {
+  final client = http ?? HttpClient();
+  try {
+    final req = await client
+        .getUrl(Uri.parse(url))
+        .timeout(const Duration(seconds: 15));
+    final res = await req.close();
+    if (res.statusCode != 200) {
+      throw HttpException('download failed: HTTP ${res.statusCode}');
+    }
+    final sink = dest.openWrite();
+    try {
+      await res.pipe(sink);
+    } finally {
+      await sink.close();
+    }
+  } finally {
+    client.close();
+  }
+}
+
+Future<void> verifySha256(File file, String want) async {
+  final digest = await sha256.bind(file.openRead()).first;
+  if (digest.toString() != want.trim().toLowerCase()) {
+    throw const FormatException('sha256 mismatch — download is corrupt');
+  }
+}
+
+// Release bundle layout is <root>/<binary> with <root>/data and <root>/lib
+// siblings. Anything else (dev runs, dart run) is not a packaged install.
+Directory? findInstallRoot(String executablePath) {
+  final dir = File(executablePath).parent;
+  if (Directory('${dir.path}/data').existsSync() &&
+      Directory('${dir.path}/lib').existsSync()) {
+    return dir;
+  }
+  return null;
+}
+
+// Extract to temp, then move every file over delete-first: opening the
+// running executable for writing throws ETXTBSY, delete+rename does not.
+Future<void> applyTarball(File tarball, Directory root) async {
+  final raw = await tarball.readAsBytes();
+  final archive = TarDecoder().decodeBytes(GZipDecoder().decodeBytes(raw));
+  final stage =
+      await Directory.systemTemp.createTemp('watch-together-update');
+  try {
+    for (final entry in archive) {
+      final name = entry.name;
+      if (name.isEmpty || name.startsWith('/') || name.contains('..')) {
+        throw FormatException('unsafe tar entry: $name');
+      }
+      final target = File('${stage.path}/$name');
+      if (entry.isDirectory) {
+        await Directory(target.path).create(recursive: true);
+      } else if (entry.isFile) {
+        await target.parent.create(recursive: true);
+        await target.writeAsBytes(entry.content as List<int>);
+      } else {
+        throw FormatException('unsupported tar entry: $name');
+      }
+    }
+    await for (final entity
+        in stage.list(recursive: true, followLinks: false)) {
+      if (entity is! File) continue;
+      final rel = entity.path.substring(stage.path.length + 1);
+      final dest = File('${root.path}/$rel');
+      await dest.parent.create(recursive: true);
+      if (await dest.exists() || await Link(dest.path).exists()) {
+        await dest.delete();
+      }
+      await entity.rename(dest.path);
+    }
+  } finally {
+    if (await stage.exists()) {
+      await stage.delete(recursive: true);
+    }
+  }
+}
+
+// Returns a process exit code: 0 ok / already current, 1 failure,
+// 2 not a packaged install (update manually).
+Future<int> runUpgrade(
+    {String currentVersion = appVersion,
+    String manifestUrl = updateManifestUrl,
+    HttpClient? http,
+    String? executablePath,
+    Directory? installRoot}) async {
+  stdout.writeln('watch-together $currentVersion (proto ${RelayConstants.protoVersion})');
+  late final UpdateManifest manifest;
+  try {
+    manifest = await fetchManifest(http: http, url: manifestUrl);
+  } catch (e) {
+    stdout.writeln('update check failed: $e');
+    return 1;
+  }
+  if (!isNewerVersion(currentVersion, manifest.version)) {
+    stdout.writeln('already up to date (${manifest.version}).');
+    return 0;
+  }
+  stdout.writeln('update available: ${manifest.version} (proto ${manifest.protocol})');
+  if (manifest.notes.isNotEmpty) {
+    stdout.writeln(manifest.notes);
+  }
+  if (manifest.protocol != RelayConstants.protoVersion) {
+    stdout.writeln('WARNING: protocol ${manifest.protocol} != ${RelayConstants.protoVersion} — '
+        'update together with everyone in the room, mixed versions cannot sync.');
+  }
+  final root = installRoot ??
+      findInstallRoot(executablePath ?? Platform.resolvedExecutable);
+  if (root == null) {
+    stdout.writeln('not a packaged install — download the tarball and update manually.');
+    return 2;
+  }
+  final tmp = await Directory.systemTemp.createTemp('watch-together-dl');
+  try {
+    final file = File('${tmp.path}/update.tar.gz');
+    stdout.writeln('downloading ${manifest.url} ...');
+    await downloadFile(manifest.url, file, http: http);
+    await verifySha256(file, manifest.sha256);
+    stdout.writeln('verified, applying over ${root.path} ...');
+    await applyTarball(file, root);
+  } catch (e) {
+    stdout.writeln('update failed: $e');
+    return 1;
+  } finally {
+    if (await tmp.exists()) {
+      await tmp.delete(recursive: true);
+    }
+  }
+  stdout.writeln('updated to ${manifest.version} — restart the app to use it.');
+  return 0;
+}