feat(agui): Add multimodal input support (image/video/audio) to AguiMessage and AguiMessageConverter

Adds support for multimodal input (image, video, audio, document) in the AG-UI extension, aligning with the AG-UI Protocol InputContent specification.

- AguiMessage.content: String -> Object (backward compatible)
- AguiMessageConverter: InputContent[] -> ContentBlock conversion
- Supports both url and data (base64) source types

Author: NoiAI

agentscope-extensions/agentscope-extensions-agui/src/main/java/io/agentscope/core/agui/converter/AguiMessageConverter.java

@@ -19,12 +19,18 @@
 import io.agentscope.core.agui.model.AguiFunctionCall;
 import io.agentscope.core.agui.model.AguiMessage;
 import io.agentscope.core.agui.model.AguiToolCall;
+import io.agentscope.core.message.AudioBlock;
+import io.agentscope.core.message.Base64Source;
 import io.agentscope.core.message.ContentBlock;
+import io.agentscope.core.message.ImageBlock;
 import io.agentscope.core.message.Msg;
 import io.agentscope.core.message.MsgRole;
+import io.agentscope.core.message.Source;
 import io.agentscope.core.message.TextBlock;
 import io.agentscope.core.message.ToolResultBlock;
 import io.agentscope.core.message.ToolUseBlock;
+import io.agentscope.core.message.URLSource;
+import io.agentscope.core.message.VideoBlock;
 import io.agentscope.core.util.JsonException;
 import io.agentscope.core.util.JsonUtils;
 import java.util.ArrayList;
@@ -37,6 +43,17 @@
  *
  * <p>This class handles the bidirectional conversion between the AG-UI protocol's
  * message format and AgentScope's internal message format.
+ *
+ * <p>Supports multimodal input per AG-UI protocol:
+ * <ul>
+ *   <li>{@code text} → {@link TextBlock}</li>
+ *   <li>{@code image} → {@link ImageBlock}</li>
+ *   <li>{@code video} → {@link VideoBlock}</li>
+ *   <li>{@code audio} → {@link AudioBlock}</li>
+ *   <li>{@code document} → {@link TextBlock} (with description)</li>
+ * </ul>
+ *
+ * <p>See https://docs.ag-ui.com/concepts/messages.md for AG-UI InputContent spec.
  */
 public class AguiMessageConverter {
     /**
@@ -54,8 +71,20 @@ public Msg toMsg(AguiMessage aguiMessage) {
         MsgRole role = convertRole(aguiMessage.getRole());
         List<ContentBlock> blocks = new ArrayList<>();
 
-        // Add text content if present
-        if (aguiMessage.getContent() != null && !aguiMessage.getContent().isEmpty()) {
+        // Handle multimodal content (InputContent array per AG-UI protocol)
+        if (aguiMessage.isMultimodalContent()) {
+            List<Map<String, Object>> parts = aguiMessage.getMultimodalContent();
+            if (parts != null) {
+                for (Map<String, Object> part : parts) {
+                    ContentBlock block = convertInputContent(part);
+                    if (block != null) {
+                        blocks.add(block);
+                    }
+                }
+            }
+        }
+        // Handle simple text content (backward compatible)
+        else if (aguiMessage.getContent() != null && !aguiMessage.getContent().isEmpty()) {
             if (aguiMessage.isToolMessage() && aguiMessage.getToolCallId() != null) {
                 // For tool messages, wrap content in ToolResultBlock
                 blocks.add(
@@ -78,6 +107,91 @@ public Msg toMsg(AguiMessage aguiMessage) {
         return Msg.builder().id(aguiMessage.getId()).role(role).content(blocks).build();
     }
 
+    /**
+     * Convert a single AG-UI InputContent part to an AgentScope ContentBlock.
+     *
+     * @param part The InputContent map from AG-UI protocol
+     * @return The converted ContentBlock, or null if type is unrecognized
+     */
+    @SuppressWarnings("unchecked")
+    private ContentBlock convertInputContent(Map<String, Object> part) {
+        String type = (String) part.get("type");
+        if (type == null) {
+            return null;
+        }
+
+        switch (type) {
+            case "text":
+                String text = (String) part.get("text");
+                return text != null ? TextBlock.builder().text(text).build() : null;
+
+            case "image":
+                Source source = extractSource(part);
+                return source != null ? ImageBlock.builder().source(source).build() : null;
+
+            case "video":
+                Source videoSource = extractSource(part);
+                return videoSource != null
+                        ? VideoBlock.builder().source(videoSource).build()
+                        : null;
+
+            case "audio":
+                Source audioSource = extractSource(part);
+                return audioSource != null
+                        ? AudioBlock.builder().source(audioSource).build()
+                        : null;
+
+            case "document":
+                // Convert document to TextBlock with description
+                Source docSource = extractSource(part);
+                if (docSource != null) {
+                    String docDesc = "[Document: " + extractMimeType(part) + "]";
+                    return TextBlock.builder().text(docDesc).build();
+                }
+                return null;
+
+            default:
+                return null;
+        }
+    }
+
+    /**
+     * Extract Source from an InputContent part.
+     * Supports both 'url' and 'data' (base64) source types.
+     */
+    @SuppressWarnings("unchecked")
+    private Source extractSource(Map<String, Object> part) {
+        Map<String, Object> sourceMap = (Map<String, Object>) part.get("source");
+        if (sourceMap == null) {
+            return null;
+        }
+
+        String sourceType = (String) sourceMap.get("type");
+        if ("url".equals(sourceType)) {
+            String url = (String) sourceMap.get("value");
+            return url != null ? new URLSource(url) : null;
+        } else if ("data".equals(sourceType)) {
+            String data = (String) sourceMap.get("value");
+            String mimeType = (String) sourceMap.get("mimeType");
+            if (data != null && mimeType != null) {
+                return new Base64Source(data, mimeType);
+            }
+        }
+        return null;
+    }
+
+    /**
+     * Extract mimeType from an InputContent part (for document type).
+     */
+    private String extractMimeType(Map<String, Object> part) {
+        @SuppressWarnings("unchecked")
+        Map<String, Object> sourceMap = (Map<String, Object>) part.get("source");
+        if (sourceMap != null) {
+            return (String) sourceMap.get("mimeType");
+        }
+        return null;
+    }
+
     /**
      * Convert an AgentScope message to an AG-UI message.
      *

agentscope-extensions/agentscope-extensions-agui/src/main/java/io/agentscope/core/agui/model/AguiMessage.java

@@ -19,6 +19,7 @@
 import com.fasterxml.jackson.annotation.JsonProperty;
 import java.util.Collections;
 import java.util.List;
+import java.util.Map;
 import java.util.Objects;
 
 /**
@@ -34,12 +35,24 @@
  *   <li>system - System instructions</li>
  *   <li>tool - Tool execution results</li>
  * </ul>
+ *
+ * <p>Content can be a simple string or a multimodal array of
+ * {@code InputContent} objects (per AG-UI protocol).
+ * See https://docs.ag-ui.com/concepts/messages.md for details.
+ *
+ * <p>InputContent array element structure:
+ * <pre>{@code
+ * { "type": "text", "text": "Hello" }
+ * { "type": "image", "source": { "type": "url", "value": "https://...", "mimeType": "image/png" } }
+ * { "type": "video", "source": { "type": "url", "value": "https://...", "mimeType": "video/mp4" } }
+ * { "type": "audio", "source": { "type": "url", "value": "https://...", "mimeType": "audio/wav" } }
+ * }</pre>
  */
 public class AguiMessage {
 
     private final String id;
     private final String role;
-    private final String content;
+    private final Object content; // String or List<map<string,object>> for multimodal
     private final List<AguiToolCall> toolCalls;
     private final String toolCallId;
 
@@ -48,15 +61,16 @@ public class AguiMessage {
      *
      * @param id The unique message ID
      * @param role The message role (user, assistant, system, tool)
-     * @param content The message content
+     * @param content The message content - may be a String or a List of InputContent objects
+     *                (multimodal input per AG-UI protocol)
      * @param toolCalls Tool calls for assistant messages (optional)
      * @param toolCallId Tool call ID for tool messages (optional)
      */
     @JsonCreator
     public AguiMessage(
             @JsonProperty("id") String id,
             @JsonProperty("role") String role,
-            @JsonProperty("content") String content,
+            @JsonProperty("content") Object content,
             @JsonProperty("toolCalls") List<AguiToolCall> toolCalls,
             @JsonProperty("toolCallId") String toolCallId) {
         this.id = Objects.requireNonNull(id, "id cannot be null");
@@ -135,12 +149,44 @@ public String getRole() {
     /**
      * Get the message content.
      *
-     * @return The content, may be null
+     * @return The content as a String if it is a simple text message, or null if
+     *         the content is multimodal (InputContent array). Use {@link #getContentObject()}
+     *         for full multimodal support.
      */
     public String getContent() {
+        return content instanceof String ? (String) content : null;
+    }
+
+    /**
+     * Get the raw content object.
+     *
+     * @return The content as an Object - either a String for simple text messages
+     *         or a List of InputContent maps for multimodal messages.
+     */
+    public Object getContentObject() {
         return content;
     }
 
+    /**
+     * Check if this message contains multimodal content (InputContent array).
+     *
+     * @return true if content is a List (multimodal), false if it's a String or null
+     */
+    public boolean isMultimodalContent() {
+        return content instanceof List;
+    }
+
+    /**
+     * Get the multimodal content as a list of InputContent objects.
+     * Each item is a Map with keys: type, text/source/etc.
+     *
+     * @return The content as a List if it is multimodal, or null if it's a simple String
+     */
+    @SuppressWarnings("unchecked")
+    public List<Map<String, Object>> getMultimodalContent() {
+        return content instanceof List ? (List<Map<String, Object>>) content : null;
+    }
+
     /**
      * Get the tool calls (for assistant messages).
      *