Emit SessionInfoUpdate after rename so clients can repaint inline

Previously the title was persisted to session_index.jsonl but the
connected client (Zed) only saw the change on the next session/list
refresh — usually after restart. Send a SessionUpdate::SessionInfoUpdate
carrying the new title so the client can update its session list
in place, no restart needed.

Covers both rename surfaces: the session/setTitle JSON-RPC and the
/rename builtin slash command both flow through handle_set_title.

Author: daniel-agentee

src/thread.rs

@@ -17,8 +17,9 @@ use agent_client_protocol::{
         PlanEntryStatus, PromptRequest, RequestPermissionOutcome, RequestPermissionRequest,
         RequestPermissionResponse, ResourceLink, SelectedPermissionOutcome, SessionConfigId,
         SessionConfigOption, SessionConfigOptionCategory, SessionConfigOptionValue,
-        SessionConfigSelectOption, SessionConfigValueId, SessionId, SessionMode, SessionModeId,
-        SessionModeState, SessionModelState, SessionNotification, SessionUpdate, StopReason,
+        SessionConfigSelectOption, SessionConfigValueId, SessionId, SessionInfoUpdate,
+        SessionMode, SessionModeId, SessionModeState, SessionModelState, SessionNotification,
+        SessionUpdate, StopReason,
         Terminal, TextContent, TextResourceContents, ToolCall, ToolCallContent, ToolCallId,
         ToolCallLocation, ToolCallStatus, ToolCallUpdate, ToolCallUpdateFields, ToolKind,
         UnstructuredCommandInput, UsageUpdate,
@@ -3427,6 +3428,13 @@ impl<A: Auth> ThreadActor<A> {
                 Error::internal_error().data(format!("failed to index thread title: {err}"))
             })?;
 
+        // Tell the connected client the title changed so it can repaint the
+        // session list without waiting for the next session/list call.
+        self.client
+            .send_notification(SessionUpdate::SessionInfoUpdate(
+                SessionInfoUpdate::new().title(title),
+            ));
+
         Ok(())
     }
 
@@ -4865,6 +4873,17 @@ mod tests {
             Some("Renamed from ACP".to_string())
         );
 
+        let notifications = client.notifications.lock().unwrap();
+        assert!(
+            notifications.iter().any(|n| matches!(
+                &n.update,
+                SessionUpdate::SessionInfoUpdate(update)
+                    if matches!(&update.title, agent_client_protocol::schema::MaybeUndefined::Value(t) if t == "Renamed from ACP")
+            )),
+            "expected a SessionInfoUpdate carrying the new title; got: {notifications:#?}"
+        );
+        drop(notifications);
+
         thread.shutdown().await?;
         std::fs::remove_dir_all(codex_home).ok();