chore: Halkyon Learn moves into apps/learn

Its server, client, app and curator, and the tools that write its
assets (maps, Anki fixtures, icons), as they are; paths are fixed in
the commits that follow.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

apps/learn/halkyon_learn_curator/test/mecab_test.dart

@@ -0,0 +1,86 @@
+import 'dart:io';
+
+import 'package:archive/archive.dart';
+import 'package:halkyon_learn_curator/src/mecab.dart';
+import 'package:test/test.dart';
+
+void main() {
+  late Directory compiled;
+  late Directory into;
+
+  setUp(() async {
+    compiled = await Directory.systemTemp.createTemp('compiled');
+    into = await Directory.systemTemp.createTemp('dictionaries');
+    for (final name in [
+      'char.bin',
+      'dicrc',
+      'matrix.bin',
+      'sys.dic',
+      'unk.dic',
+    ]) {
+      await File('${compiled.path}/$name').writeAsString('$name of IPADIC');
+    }
+  });
+  tearDown(() async {
+    await compiled.delete(recursive: true);
+    await into.delete(recursive: true);
+  });
+
+  test('packs the files MeCab reads, the licence and an empty mecabrc into '
+      'one gzipped tar beside the dictionary files', () async {
+    final licence = File('${compiled.path}/copyright')
+      ..writeAsStringSync('Copyright 2000, 2001, 2002, 2003 Nara Institute');
+
+    final packed = await packIpadic(compiled, into, licence: licence);
+
+    expect(packed?.path, '${into.path}/$ipadicFile');
+    final files = {
+      for (final file in TarDecoder().decodeBytes(
+        const GZipDecoder().decodeBytes(packed!.readAsBytesSync()),
+      ))
+        file.name: String.fromCharCodes(file.content),
+    };
+    expect(files.keys, {
+      'char.bin',
+      'dicrc',
+      'matrix.bin',
+      'sys.dic',
+      'unk.dic',
+      'COPYING',
+      'mecabrc',
+    });
+    expect(files['sys.dic'], 'sys.dic of IPADIC');
+    expect(files['COPYING'], startsWith('Copyright'));
+    expect(files['mecabrc'], isEmpty);
+    // Nothing the server would load as a dictionary.
+    expect(
+      into.listSync().where(
+        (file) =>
+            file.path.endsWith('.jsonl') || file.path.endsWith('.jsonl.gz'),
+      ),
+      isEmpty,
+    );
+  });
+
+  test('leaves the pack as it is when the dictionary is the same, so devices '
+      'download it again only once it changed', () async {
+    final first = await packIpadic(compiled, into);
+    final bytes = first!.readAsBytesSync();
+
+    expect(await packIpadic(compiled, into), isNull);
+    expect(File('${into.path}/$ipadicFile').readAsBytesSync(), bytes);
+
+    await File('${compiled.path}/sys.dic').writeAsString('a newer IPADIC');
+    expect(await packIpadic(compiled, into), isNotNull);
+  });
+
+  test('refuses a dictionary missing a file MeCab reads', () async {
+    await File('${compiled.path}/matrix.bin').delete();
+
+    await expectLater(
+      packIpadic(compiled, into),
+      throwsA(isA<FileSystemException>()),
+    );
+    expect(File('${into.path}/$ipadicFile').existsSync(), isFalse);
+  });
+}