From 6357227f7f47d9725d29eeefc81d28b878b4adac Mon Sep 17 00:00:00 2001
From: Jhin Lee <leehack@gmail.com>
Date: Mon, 1 Jun 2026 03:48:30 -0400
Subject: [PATCH] Keep image content theme parse-only

---
 lib/src/types/content.dart | 5 ++++-
 test/types_test.dart       | 9 ++++++---
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/lib/src/types/content.dart b/lib/src/types/content.dart
index 42c612b5..cb22fbf1 100644
--- a/lib/src/types/content.dart
+++ b/lib/src/types/content.dart
@@ -267,7 +267,6 @@ sealed class Content {
           final ImageContent c => {
               'data': c.data,
               'mimeType': c.mimeType,
-              if (c.theme != null) 'theme': c.theme,
               if (c.annotations != null) 'annotations': c.annotations!.toJson(),
               if (c.meta != null)
                 '_meta': readJsonObject(c.meta, 'ImageContent._meta'),
@@ -346,6 +345,10 @@ class ImageContent extends Content {
   final String mimeType;
 
   /// Optional theme hint for legacy icon usage (`light` | `dark`).
+  ///
+  /// This field is parsed for backwards compatibility with older icon-shaped
+  /// payloads. MCP ImageContent content blocks do not serialize `theme`; use
+  /// [McpIcon.theme] for advertised icons.
   final String? theme;
 
   /// Optional annotations for the content block.
diff --git a/test/types_test.dart b/test/types_test.dart
index 250258ee..23679064 100644
--- a/test/types_test.dart
+++ b/test/types_test.dart
@@ -494,7 +494,7 @@ void main() {
       expect(deserialized.mimeType, equals('image/png'));
     });
 
-    test('ImageContent supports optional theme', () {
+    test('ImageContent parses legacy theme without serializing it', () {
       final content = const ImageContent(
         data: 'base64data',
         mimeType: 'image/png',
@@ -502,9 +502,12 @@ void main() {
       );
 
       final json = content.toJson();
-      expect(json['theme'], equals('dark'));
+      expect(json, isNot(contains('theme')));
 
-      final deserialized = ImageContent.fromJson(json);
+      final deserialized = ImageContent.fromJson({
+        ...json,
+        'theme': 'dark',
+      });
       expect(deserialized.theme, equals('dark'));
     });