perf(images): size decoded covers from layout constraints

lib/widgets/cached_cover_image.dart

@@ -41,10 +41,38 @@ class CachedCoverImage extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final autoMemCacheWidth =
+    if (width != null ||
+        height != null ||
+        memCacheWidth != null ||
+        memCacheHeight != null) {
+      return _buildImage(context, const BoxConstraints());
+    }
+    // Grid cells size their children through constraints rather than explicit
+    // width/height. Use those bounds for decoding as well as explicit sizes.
+    return LayoutBuilder(
+      builder: (context, constraints) => _buildImage(context, constraints),
+    );
+  }
+
+  Widget _buildImage(BuildContext context, BoxConstraints constraints) {
+    var autoMemCacheWidth =
         memCacheWidth ?? _cacheExtentForLogicalSize(context, width);
-    final autoMemCacheHeight =
+    var autoMemCacheHeight =
         memCacheHeight ?? _cacheExtentForLogicalSize(context, height);
+    if (autoMemCacheWidth == null && autoMemCacheHeight == null) {
+      // Infer one axis to preserve the source aspect ratio and respect any
+      // explicit decode override used by large artwork/header consumers.
+      autoMemCacheWidth = _cacheExtentForLogicalSize(
+        context,
+        constraints.maxWidth,
+      );
+      if (autoMemCacheWidth == null) {
+        autoMemCacheHeight = _cacheExtentForLogicalSize(
+          context,
+          constraints.maxHeight,
+        );
+      }
+    }
     final diskCacheWidth = resizeDiskCache ? autoMemCacheWidth : null;
     final diskCacheHeight = resizeDiskCache ? autoMemCacheHeight : null;
     final image = CachedNetworkImage(

test/cached_cover_decode_test.dart

@@ -0,0 +1,43 @@
+import 'package:cached_network_image/cached_network_image.dart';
+import 'package:flutter/material.dart';
+import 'package:spotiflac_android/widgets/cached_cover_image.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+  for (final explicit in [false, true]) {
+    testWidgets(
+      'grid decode follows constraints, explicit override=$explicit',
+      (tester) async {
+        await tester.pumpWidget(
+          MaterialApp(
+            home: MediaQuery(
+              data: const MediaQueryData(devicePixelRatio: 2),
+              child: Center(
+                child: SizedBox.square(
+                  dimension: 180,
+                  child: CachedCoverImage(
+                    imageUrl: 'https://example.invalid/cover.png',
+                    memCacheWidth: explicit ? 1200 : null,
+                    errorWidget: (_, _, _) => const SizedBox(),
+                  ),
+                ),
+              ),
+            ),
+          ),
+        );
+        final image = tester.widget<CachedNetworkImage>(
+          find.byType(CachedNetworkImage),
+        );
+        expect(image.memCacheWidth, explicit ? 1200 : 360);
+        expect(image.memCacheHeight, isNull);
+        expect(image.maxWidthDiskCache, isNull);
+        expect(
+          tester.getSize(find.byType(CachedCoverImage)),
+          const Size(180, 180),
+        );
+        await tester.pumpWidget(const SizedBox());
+      },
+    );
+  }
+}