add agent_message_clear

impls agentclientprotocol/agent-client-protocol#465

Author: steve02081504

examples/client.rs

@@ -90,7 +90,12 @@ impl acp::Client for ExampleClient {
                 };
                 println!("| Agent: {text}");
             }
-            _ => {} // Handle future variants gracefully
+            acp::SessionUpdate::AgentMessageClear => {
+                // Clear accumulated streamed content for the current agent message.
+                // Subsequent agent_message_chunk will append from empty.
+                println!("| Agent: (message cleared)");
+            }
+            _ => {} // Handle other variants gracefully
         }
         Ok(())
     }

src/agent-client-protocol/CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## [Unreleased]
+
+### Added
+
+- Support for `agent_message_clear` session update (RFD [agent_message_clear](https://github.com/agentclientprotocol/agent-client-protocol/blob/main/docs/rfds/agent_message_clear.md)): clients can clear accumulated streamed content for the current agent message; example client and tests updated.
+
 ## [0.9.4](https://github.com/agentclientprotocol/rust-sdk/compare/v0.9.3...v0.9.4) - 2026-02-04
 
 ### Added

src/agent-client-protocol/src/rpc_tests.rs

@@ -627,6 +627,9 @@ async fn test_full_conversation_flow() {
                             found_final_message = true;
                         }
                     }
+                    SessionUpdate::AgentMessageClear => {
+                        // Client would clear accumulated message; test just verifies we receive it.
+                    }
                     SessionUpdate::ToolCall(_) => {
                         found_tool_call = true;
                     }
@@ -647,6 +650,71 @@ async fn test_full_conversation_flow() {
         .await;
 }
 
+#[tokio::test]
+async fn test_agent_message_clear_sequence() {
+    let local_set = tokio::task::LocalSet::new();
+    local_set
+        .run_until(async {
+            let client = TestClient::new();
+            let agent = TestAgent::new();
+            let (agent_conn, client_conn) = create_connection_pair(&client, &agent);
+
+            let session_id = SessionId::new("clear-test-session");
+            agent_conn
+                .prompt(PromptRequest::new(
+                    session_id.clone(),
+                    vec!["Say hello then replace with goodbye".into()],
+                ))
+                .await
+                .expect("prompt failed");
+
+            // Agent sends draft, then clear, then final (RFD agent_message_clear usage pattern)
+            client_conn
+                .session_notification(SessionNotification::new(
+                    session_id.clone(),
+                    SessionUpdate::AgentMessageChunk(ContentChunk::new("Drafting...".into())),
+                ))
+                .await
+                .expect("session_notification failed");
+            client_conn
+                .session_notification(SessionNotification::new(
+                    session_id.clone(),
+                    SessionUpdate::AgentMessageClear,
+                ))
+                .await
+                .expect("session_notification failed");
+            client_conn
+                .session_notification(SessionNotification::new(
+                    session_id.clone(),
+                    SessionUpdate::AgentMessageChunk(ContentChunk::new("Here is the final result.".into())),
+                ))
+                .await
+                .expect("session_notification failed");
+
+            for _ in 0..10 {
+                tokio::task::yield_now().await;
+            }
+
+            let updates = client.session_notifications.lock().unwrap();
+            let mut clear_seen = false;
+            let mut final_chunk_seen = false;
+            for n in updates.iter() {
+                match &n.update {
+                    SessionUpdate::AgentMessageClear => clear_seen = true,
+                    SessionUpdate::AgentMessageChunk(ContentChunk { content: ContentBlock::Text(t), .. }) => {
+                        if t.text.contains("final result") {
+                            final_chunk_seen = true;
+                        }
+                    }
+                    _ => {}
+                }
+            }
+            assert!(clear_seen, "Client should receive agent_message_clear");
+            assert!(final_chunk_seen, "Client should receive final chunk after clear");
+        })
+        .await;
+}
+
 #[tokio::test]
 async fn test_extension_methods_and_notifications() {
     let local_set = tokio::task::LocalSet::new();

src/sacp-test/src/test_client.rs

@@ -42,11 +42,17 @@ where
     JrHandlerChain::new()
         .name("test-client")
         .on_receive_notification(async |notif: SessionNotification, _cx| {
-            // Collect text from AgentMessageChunk updates
-            if let SessionUpdate::AgentMessageChunk(chunk) = &notif.update
-                && let ContentBlock::Text(text_content) = &chunk.content
-            {
-                collected_text.push_str(&text_content.text);
+            // Collect text from AgentMessageChunk updates; clear on AgentMessageClear
+            match &notif.update {
+                SessionUpdate::AgentMessageChunk(chunk) => {
+                    if let ContentBlock::Text(text_content) = &chunk.content {
+                        collected_text.push_str(&text_content.text);
+                    }
+                }
+                SessionUpdate::AgentMessageClear => {
+                    collected_text.clear();
+                }
+                _ => {}
             }
             Ok(())
         })