refactor(agui): redesign event dispatching with strategy pattern and deferred queue

agentscope-core/src/main/java/io/agentscope/core/message/ContentBlock.java

@@ -35,6 +35,7 @@
  *   <li>{@link VideoBlock} - Video content (URL or Base64)
  *   <li>{@link ToolUseBlock} - Tool execution requests
  *   <li>{@link ToolResultBlock} - Tool execution results
+ *   <li>{@link CustomBlock} - Custom extension block to trigger AG-UI Custom events
  * </ul>
  *
  * <p>Uses Jackson annotations for polymorphic JSON serialization with the "type" discriminator
@@ -49,7 +50,8 @@
     @JsonSubTypes.Type(value = AudioBlock.class, name = "audio"),
     @JsonSubTypes.Type(value = VideoBlock.class, name = "video"),
     @JsonSubTypes.Type(value = ToolUseBlock.class, name = "tool_use"),
-    @JsonSubTypes.Type(value = ToolResultBlock.class, name = "tool_result")
+    @JsonSubTypes.Type(value = ToolResultBlock.class, name = "tool_result"),
+    @JsonSubTypes.Type(value = CustomBlock.class, name = "custom")
 })
 public sealed class ContentBlock implements State
         permits TextBlock,
@@ -58,4 +60,5 @@ public sealed class ContentBlock implements State
                 VideoBlock,
                 ThinkingBlock,
                 ToolUseBlock,
-                ToolResultBlock {}
+                ToolResultBlock,
+                CustomBlock {}

agentscope-core/src/main/java/io/agentscope/core/message/CustomBlock.java

@@ -0,0 +1,114 @@
+/*
+ * Copyright 2024-2026 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package io.agentscope.core.message;
+
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+/**
+ * Represents a custom extension block specifically designed to trigger AG-UI Custom events.
+ *
+ * <p>This block allows for the transmission of arbitrary JSON-serializable payloads
+ * to the frontend. It is commonly used for real-time progress pushes, workflow
+ * state changes, and any other customized interactive behaviors within the AG-UI protocol.
+ *
+ * <p>The name identifies the custom event type, and the value can be a Map, String,
+ * Number, or any JSON-serializable object containing the event payload.
+ */
+public final class CustomBlock extends ContentBlock {
+
+    private final String name;
+    private final Object value;
+
+    /**
+     * Creates a new custom block for JSON deserialization.
+     *
+     * @param name The name of the custom event (null will be converted to empty string)
+     * @param value The arbitrary payload value associated with the event
+     */
+    @JsonCreator
+    public CustomBlock(@JsonProperty("name") String name, @JsonProperty("value") Object value) {
+        this.name = name != null ? name : "";
+        this.value = value;
+    }
+
+    /**
+     * Gets the name of this custom block.
+     *
+     * @return The event name
+     */
+    public String getName() {
+        return name;
+    }
+
+    /**
+     * Gets the payload value of this custom block.
+     *
+     * @return The payload object
+     */
+    public Object getValue() {
+        return value;
+    }
+
+    /**
+     * Creates a new builder for constructing CustomBlock instances.
+     *
+     * @return A new builder instance
+     */
+    public static Builder builder() {
+        return new Builder();
+    }
+
+    /**
+     * Builder for constructing CustomBlock instances.
+     */
+    public static class Builder {
+
+        private String name;
+        private Object value;
+
+        /**
+         * Sets the name for the custom block event.
+         *
+         * @param name The custom event name
+         * @return This builder for chaining
+         */
+        public Builder name(String name) {
+            this.name = name;
+            return this;
+        }
+
+        /**
+         * Sets the arbitrary payload value for the block.
+         *
+         * @param value payload object
+         * @return This builder for chaining
+         */
+        public Builder value(Object value) {
+            this.value = value;
+            return this;
+        }
+
+        /**
+         * Builds a new CustomBlock with the configured properties.
+         *
+         * @return A new CustomBlock instance (null name will be converted to empty string)
+         */
+        public CustomBlock build() {
+            return new CustomBlock(name != null ? name : "", value);
+        }
+    }
+}