perf(theme): cache the hash of token colours instead of rehashing per build

lib/core/editor/querya_code_editor.dart

@@ -97,7 +97,7 @@ class _QueryaCodeEditorState extends State<QueryaCodeEditor> {
     if (controller is! QueryaHighlightController) return;
 
     final editor = queryaTheme.editor;
-    final tokenHash = Object.hashAll(queryaTheme.tokenColors);
+    final tokenHash = queryaTheme.tokenColorsHash;
     if (_lastEditorTheme == editor && _lastTokenColorsHash == tokenHash) {
       return;
     }

lib/core/editor/syntax_highlight_service.dart

@@ -64,7 +64,7 @@ abstract final class SyntaxHighlightService {
     final cacheKey = Object.hash(
       language,
       queryaTheme.editor,
-      Object.hashAll(queryaTheme.tokenColors),
+      queryaTheme.tokenColorsHash,
     );
     final cached = _pairCache[cacheKey];
     if (cached != null) return cached;

lib/core/theme/querya_theme.dart

@@ -24,6 +24,17 @@ class QueryaTheme {
   /// VS Code `tokenColors` for syntax highlighting (imported themes).
   final List<TokenColorRule> tokenColors;
 
+  /// Hashes of token colour lists, keyed by the list itself: themes built by
+  /// [copyWith] and [lerp] (one per animation frame) share the list, so each
+  /// list is hashed once however many themes point at it.
+  static final Expando<int> _tokenColorsHashes =
+      Expando<int>('QueryaTheme.tokenColorsHash');
+
+  /// Hash of [tokenColors], computed once per list (#1353): the editor asks
+  /// for it on every build, and a full VS Code theme has hundreds of rules.
+  int get tokenColorsHash =>
+      _tokenColorsHashes[tokenColors] ??= Object.hashAll(tokenColors);
+
   static const QueryaTheme darkDefault = QueryaTheme(
     workbench: QueryaWorkbenchTheme.darkDefault,
     editor: QueryaEditorTheme.darkDefault,

test/core/theme/querya_theme_token_colors_hash_test.dart

@@ -0,0 +1,51 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:querya_desktop/core/theme/parser/vscode_theme_manifest.dart';
+import 'package:querya_desktop/core/theme/querya_theme.dart';
+
+void main() {
+  const rules = [
+    TokenColorRule(scopes: ['keyword'], foreground: '#ff0000'),
+    TokenColorRule(scopes: ['string', 'string.quoted'], foreground: '#00ff00'),
+  ];
+
+  group('QueryaTheme.tokenColorsHash (#1353)', () {
+    test('equals the hash of the token colours', () {
+      final theme = QueryaTheme.darkDefault.copyWith(tokenColors: rules);
+
+      expect(theme.tokenColorsHash, Object.hashAll(rules));
+    });
+
+    test('is stable across reads', () {
+      final theme = QueryaTheme.darkDefault.copyWith(tokenColors: rules);
+
+      expect(theme.tokenColorsHash, theme.tokenColorsHash);
+    });
+
+    test('themes sharing a list share the hash', () {
+      final a = QueryaTheme.darkDefault.copyWith(tokenColors: rules);
+      final b = a.copyWith(brightness: a.brightness);
+      final mid = QueryaTheme.lerp(a, b, 0.25);
+
+      expect(b.tokenColorsHash, a.tokenColorsHash);
+      expect(mid.tokenColorsHash, a.tokenColorsHash);
+    });
+
+    test('different rules give a different hash', () {
+      final a = QueryaTheme.darkDefault.copyWith(tokenColors: rules);
+      final b = QueryaTheme.darkDefault.copyWith(
+        tokenColors: const [
+          TokenColorRule(scopes: ['comment'], foreground: '#888888'),
+        ],
+      );
+
+      expect(a.tokenColorsHash, isNot(b.tokenColorsHash));
+    });
+
+    test('a theme without token colours has the empty-list hash', () {
+      expect(
+        QueryaTheme.darkDefault.tokenColorsHash,
+        Object.hashAll(const <TokenColorRule>[]),
+      );
+    });
+  });
+}