core: split message part updates into delta events for smoother streaming

Streaming text and reasoning content now uses incremental delta events instead of sending full message parts on each update. This reduces bandwidth and improves real-time response smoothness in the TUI.

packages/sdk/js/src/v2/gen/types.gen.ts

@@ -480,7 +480,17 @@ export type EventMessagePartUpdated = {
   type: "message.part.updated"
   properties: {
     part: Part
-    delta?: string
+  }
+}
+
+export type EventMessagePartDelta = {
+  type: "message.part.delta"
+  properties: {
+    sessionID: string
+    messageID: string
+    partID: string
+    field: string
+    delta: string
   }
 }
 
@@ -650,10 +660,6 @@ export type Todo = {
    * Priority level of the task: high, medium, low
    */
   priority: string
-  /**
-   * Unique identifier for the todo item
-   */
-  id: string
 }
 
 export type EventTodoUpdated = {
@@ -896,6 +902,7 @@ export type Event =
   | EventMessageUpdated
   | EventMessageRemoved
   | EventMessagePartUpdated
+  | EventMessagePartDelta
   | EventMessagePartRemoved
   | EventPermissionAsked
   | EventPermissionReplied