Emit final snapshot before run finished event

sdks/typescript/packages/client/src/apply/__tests__/default.text-message.test.ts

@@ -1,6 +1,6 @@
 import { Subject } from "rxjs";
 import { toArray } from "rxjs/operators";
-import { firstValueFrom } from "rxjs";
+import { firstValueFrom, of } from "rxjs";
 import {
   BaseEvent,
   EventType,
@@ -9,6 +9,7 @@ import {
   TextMessageContentEvent,
   TextMessageEndEvent,
   RunAgentInput,
+  RunFinishedEvent,
 } from "@ag-ui/core";
 import { defaultApplyEvents } from "../default";
 import { AbstractAgent } from "@/agent";
@@ -188,4 +189,59 @@ describe("defaultApplyEvents with text messages", () => {
     // Verify no additional updates after either TEXT_MESSAGE_END
     expect(stateUpdates.length).toBe(4);
   });
+
+  it("should emit a messages snapshot when the run finishes", async () => {
+    const initialState: RunAgentInput = {
+      messages: [],
+      state: {},
+      threadId: "test-thread",
+      runId: "test-run",
+      tools: [],
+      context: [],
+    };
+
+    const subscriber = {
+      onMessagesSnapshotEvent: jest.fn(),
+      onEvent: jest.fn(),
+    };
+
+    const events: BaseEvent[] = [
+      {
+        type: EventType.TEXT_MESSAGE_START,
+        messageId: "msg-1",
+        role: "assistant",
+      } as TextMessageStartEvent,
+      {
+        type: EventType.TEXT_MESSAGE_CONTENT,
+        messageId: "msg-1",
+        delta: "Hello world!",
+      } as TextMessageContentEvent,
+      {
+        type: EventType.TEXT_MESSAGE_END,
+        messageId: "msg-1",
+      } as TextMessageEndEvent,
+      {
+        type: EventType.RUN_FINISHED,
+        threadId: "test-thread",
+        runId: "test-run",
+      } as RunFinishedEvent,
+    ];
+
+    const result$ = defaultApplyEvents(initialState, of(...events), FAKE_AGENT, [subscriber as any]);
+    const mutations = await firstValueFrom(result$.pipe(toArray()));
+
+    expect(subscriber.onMessagesSnapshotEvent).toHaveBeenCalledTimes(1);
+    const snapshotArgs = subscriber.onMessagesSnapshotEvent.mock.calls[0][0];
+    expect(snapshotArgs.event.type).toBe(EventType.MESSAGES_SNAPSHOT);
+    expect(snapshotArgs.event.messages).toHaveLength(1);
+    expect(snapshotArgs.event.messages?.[0]?.content).toBe("Hello world!");
+
+    const eventTypes = subscriber.onEvent.mock.calls.map((call) => call[0].event.type);
+    expect(eventTypes[eventTypes.length - 2]).toBe(EventType.MESSAGES_SNAPSHOT);
+    expect(eventTypes[eventTypes.length - 1]).toBe(EventType.RUN_FINISHED);
+
+    const finalMutation = mutations[mutations.length - 1];
+    expect(finalMutation.messages).toHaveLength(1);
+    expect(finalMutation.messages?.[0]?.content).toBe("Hello world!");
+  });
 });

sdks/typescript/packages/client/src/apply/default.ts

@@ -69,8 +69,59 @@ export const defaultApplyEvents = (
     return EMPTY;
   };
 
+  const emitMessagesSnapshot = async () => {
+    const snapshotEvent: MessagesSnapshotEvent = {
+      type: EventType.MESSAGES_SNAPSHOT,
+      messages: structuredClone_(messages),
+    };
+
+    const snapshotOnEventMutation = await runSubscribersWithMutation(
+      subscribers,
+      messages,
+      state,
+      (subscriber, messages, state) =>
+        subscriber.onEvent?.({
+          event: snapshotEvent,
+          agent,
+          input,
+          messages,
+          state,
+        }),
+    );
+    applyMutation(snapshotOnEventMutation);
+
+    if (snapshotOnEventMutation.stopPropagation === true) {
+      return;
+    }
+
+    snapshotEvent.messages = structuredClone_(messages);
+
+    const snapshotMutation = await runSubscribersWithMutation(
+      subscribers,
+      messages,
+      state,
+      (subscriber, messages, state) =>
+        subscriber.onMessagesSnapshotEvent?.({
+          event: snapshotEvent,
+          messages,
+          state,
+          agent,
+          input,
+        }),
+    );
+    applyMutation(snapshotMutation);
+
+    if (snapshotMutation.stopPropagation !== true && snapshotMutation.messages === undefined) {
+      applyMutation({ messages: structuredClone_(messages) });
+    }
+  };
+
   return events$.pipe(
     concatMap(async (event) => {
+      if (event.type === EventType.RUN_FINISHED) {
+        await emitMessagesSnapshot();
+      }
+
       const mutation = await runSubscribersWithMutation(
         subscribers,
         messages,