Fix structured output multi-turn conversation error

lib/ruby_llm/providers/openai/media.rb

@@ -8,7 +8,10 @@ module Media
         module_function
 
         def format_content(content) # rubocop:disable Metrics/PerceivedComplexity
-          return content.value if content.is_a?(RubyLLM::Content::Raw)
+          if content.is_a?(RubyLLM::Content::Raw)
+            value = content.value
+            return (value.is_a?(Hash) || value.is_a?(Array)) ? value.to_json : value
+          end
           return content.to_json if content.is_a?(Hash) || content.is_a?(Array)
           return content unless content.is_a?(Content)
 

spec/ruby_llm/active_record/acts_as_spec.rb

@@ -159,6 +159,30 @@ def execute(expression:)
       expect(saved_message.role).to eq('assistant')
       expect(saved_message.content_raw).to eq({ 'name' => 'Alice', 'age' => 25 })
     end
+
+    it 'supports multi-turn conversations with structured responses' do
+      chat = Chat.create!(model: model)
+
+      schema = {
+        type: 'object',
+        properties: {
+          country: { type: 'string' }
+        },
+        required: %w[country],
+        additionalProperties: false
+      }
+
+      chat.with_schema(schema)
+
+      # First turn
+      chat.ask('What country is Paris in?')
+
+      # Second turn - this should not raise an error
+      response = chat.ask('What about Berlin?')
+
+      expect(response.content).to be_a(Hash)
+      expect(response.content['country']).to eq('Germany')
+    end
   end
 
   describe 'parameter passing' do