FIX: Malformed message in systemless + inline img scenario

lib/ai_helper/assistant.rb

@@ -154,7 +154,6 @@ def generate_image_caption(upload, user)
                 upload_ids: [upload.id],
               },
             ],
-            skip_validations: true,
           )
 
         DiscourseAi::Completions::Llm.proxy(SiteSetting.ai_helper_image_caption_model).generate(

lib/completions/dialects/open_ai_compatible.rb

@@ -29,9 +29,16 @@ def translate
 
           return translated unless llm_model.lookup_custom_param("disable_system_prompt")
 
-          system_and_user_msgs = translated.shift(2)
-          user_msg = system_and_user_msgs.last
-          user_msg[:content] = [system_and_user_msgs.first[:content], user_msg[:content]].join("\n")
+          system_msg, user_msg = translated.shift(2)
+
+          if user_msg[:content].is_a?(Array) # Has inline images.
+            user_msg[:content].first[:text] = [
+              system_msg[:content],
+              user_msg[:content].first[:text],
+            ].join("\n")
+          else
+            user_msg[:content] = [system_msg[:content], user_msg[:content]].join("\n")
+          end
 
           translated.unshift(user_msg)
         end
@@ -79,16 +86,14 @@ def inline_images(content, message)
           return content if encoded_uploads.blank?
 
           content_w_imgs =
-            encoded_uploads.reduce([]) do |memo, details|
+            encoded_uploads.reduce([{ type: "text", text: message[:content] }]) do |memo, details|
               memo << {
                 type: "image_url",
                 image_url: {
                   url: "data:#{details[:mime_type]};base64,#{details[:base64]}",
                 },
               }
             end
-
-          content_w_imgs << { type: "text", text: message[:content] }
         end
       end
     end

lib/completions/prompt.rb

@@ -12,7 +12,6 @@ def initialize(
         system_message_text = nil,
         messages: [],
         tools: [],
-        skip_validations: false,
         topic_id: nil,
         post_id: nil,
         max_pixels: nil
@@ -26,7 +25,6 @@ def initialize(
         @post_id = post_id
 
         @messages = []
-        @skip_validations = skip_validations
 
         if system_message_text
           system_message = { type: :system, content: system_message_text }
@@ -68,7 +66,6 @@ def encoded_uploads(message)
       private
 
       def validate_message(message)
-        return if @skip_validations
         valid_types = %i[system user model tool tool_call]
         if !valid_types.include?(message[:type])
           raise ArgumentError, "message type must be one of #{valid_types}"
@@ -91,7 +88,6 @@ def validate_message(message)
       end
 
       def validate_turn(last_turn, new_turn)
-        return if @skip_validations
         valid_types = %i[tool tool_call model user]
         raise INVALID_TURN if !valid_types.include?(new_turn[:type])
 

spec/lib/completions/dialects/open_ai_compatible_spec.rb

@@ -2,6 +2,10 @@
 
 RSpec.describe DiscourseAi::Completions::Dialects::OpenAiCompatible do
   context "when system prompts are disabled" do
+    fab!(:model) do
+      Fabricate(:vllm_model, vision_enabled: true, provider_params: { disable_system_prompt: true })
+    end
+
     it "merges the system prompt into the first message" do
       system_msg = "This is a system message"
       user_msg = "user message"
@@ -11,15 +15,56 @@
           messages: [{ type: :user, content: user_msg }],
         )
 
-      model = Fabricate(:vllm_model, provider_params: { disable_system_prompt: true })
-
       translated_messages = described_class.new(prompt, model).translate
 
       expect(translated_messages.length).to eq(1)
       expect(translated_messages).to contain_exactly(
         { role: "user", content: [system_msg, user_msg].join("\n") },
       )
     end
+
+    context "when the prompt has inline images" do
+      let(:image100x100) { plugin_file_from_fixtures("100x100.jpg") }
+
+      it "produces a valid message" do
+        upload = UploadCreator.new(image100x100, "image.jpg").create_for(Discourse.system_user.id)
+        prompt =
+          DiscourseAi::Completions::Prompt.new(
+            "You are a bot specializing in image captioning.",
+            messages: [
+              {
+                type: :user,
+                content: "Describe this image in a single sentence.",
+                upload_ids: [upload.id],
+              },
+            ],
+          )
+        encoded_upload =
+          DiscourseAi::Completions::UploadEncoder.encode(
+            upload_ids: [upload.id],
+            max_pixels: prompt.max_pixels,
+          ).first
+
+        translated_messages = described_class.new(prompt, model).translate
+
+        expect(translated_messages.length).to eq(1)
+
+        expected_user_message = {
+          role: "user",
+          content: [
+            { type: "text", text: prompt.messages.map { |m| m[:content] }.join("\n") },
+            {
+              type: "image_url",
+              image_url: {
+                url: "data:#{encoded_upload[:mime_type]};base64,#{encoded_upload[:base64]}",
+              },
+            },
+          ],
+        }
+
+        expect(translated_messages).to contain_exactly(expected_user_message)
+      end
+    end
   end
 
   context "when system prompts are enabled" do