fix(gateway): streamed chat text stalls mid-answer until the next agent event (#119566)

* fix(gateway): flush trailing chat deltas

Keep the fixed-deadline wake-up on the existing chat run record so terminal, abort, and shutdown cleanup cancel it at the lifecycle owner. Normalize voice runs onto their unique per-turn ID instead of compensating for a stale client alias downstream.

Fixes #119557

Co-authored-by: Serghei <43180231+xyrolle@users.noreply.github.com>

* test(gateway): drop obsolete delta length assertions

Remove stale fixtures and assertions for the write-only chat delta length field deleted by the owner-boundary repair.

Co-authored-by: Serghei <43180231+xyrolle@users.noreply.github.com>

* fix(gateway): preserve chat run state type contract

Keep the optional delta length field and its cleanup semantics in the exported ChatRunState closure without restoring runtime writes.

Co-authored-by: Serghei <43180231+xyrolle@users.noreply.github.com>

* refactor(gateway): hide chat delta timer from SDK shape

Keep the trailing wake physically on each run record while exposing it only through internal state-module accessors, preserving the public ChatRunState closure.

Co-authored-by: Serghei <43180231+xyrolle@users.noreply.github.com>

* refactor(gateway): narrow chat delta timer access

Use one Gateway-internal record accessor so the run-owned timer remains outside the public ChatRunState shape without extra state maps.

Co-authored-by: Serghei <43180231+xyrolle@users.noreply.github.com>

* refactor(gateway): keep chat timer casts private

Keep the run-owned timer invisible to the generated Plugin SDK closure by using module-private casts in each owning Gateway module.

Co-authored-by: Serghei <43180231+xyrolle@users.noreply.github.com>

---------

Co-authored-by: Peter Steinberger <steipete@gmail.com>

src/gateway/server-chat-state.test.ts

@@ -17,7 +17,6 @@ describe("createChatRunState", () => {
       planSnapshot: { steps: [{ step: "Inspect", status: "in_progress" }] },
       bufferUpdatedAt: 1,
       deltaSentAt: 2,
-      deltaLastBroadcastLen: 9,
       deltaLastBroadcastText: "projected",
       agentText: { assistant: { lastSentAt: 3 } },
       abortMarker: createChatAbortMarker(4),

src/gateway/server-chat-state.ts

@@ -104,6 +104,11 @@ type ChatRunToolRecipientState = {
   finalizedAt?: number;
 };
 
+type PendingChatDeltaFlush = {
+  timer: NodeJS.Timeout;
+  flush: () => void;
+};
+
 type ChatRunRecord = {
   registrations?: ChatRunEntry[];
   rawBuffer?: string;
@@ -126,6 +131,11 @@ type ChatRunRecord = {
   toolRecipient?: ChatRunToolRecipientState;
 };
 
+type InternalChatRunRecord = ChatRunRecord & {
+  /** Fixed-deadline trailing wake-up owned by this run's buffered state. */
+  pendingDeltaFlush?: PendingChatDeltaFlush;
+};
+
 type ChatRunRecordStore = {
   runs: Map<string, ChatRunRecord>;
   getOrCreate: (runId: string) => ChatRunRecord;
@@ -153,6 +163,19 @@ function createChatRunRecordStore(): ChatRunRecordStore {
   return { runs, getOrCreate, releaseIfEmpty };
 }
 
+function internalChatRunRecord(record: ChatRunRecord): InternalChatRunRecord {
+  return record;
+}
+
+function clearPendingChatDeltaFlush(record: ChatRunRecord): void {
+  const internal = internalChatRunRecord(record);
+  if (!internal.pendingDeltaFlush) {
+    return;
+  }
+  clearTimeout(internal.pendingDeltaFlush.timer);
+  delete internal.pendingDeltaFlush;
+}
+
 export type ChatRunRegistry = {
   add: (sessionId: string, entry: ChatRunRegistration) => void;
   peek: (sessionId: string) => ChatRunEntry | undefined;
@@ -274,11 +297,15 @@ export function createChatRunState(): ChatRunState {
     delete record.deltaSentAt;
     delete record.deltaLastBroadcastLen;
     delete record.deltaLastBroadcastText;
+    clearPendingChatDeltaFlush(record);
     delete record.agentText;
     store.releaseIfEmpty(runId);
   };
 
   const clear = () => {
+    for (const record of store.runs.values()) {
+      clearPendingChatDeltaFlush(record);
+    }
     store.runs.clear();
   };
 

src/gateway/server-chat.agent-events.test.ts

@@ -239,6 +239,13 @@ describe("agent event handler", () => {
     return broadcast.mock.calls.filter(([event]) => event === "chat");
   }
 
+  function chatDeltaTexts(broadcast: ReturnType<typeof vi.fn>) {
+    return chatBroadcastCalls(broadcast)
+      .map(([, payload]) => payload as { state?: string; deltaText?: string })
+      .filter((payload) => payload.state === "delta")
+      .map((payload) => payload.deltaText);
+  }
+
   function agentBroadcastCalls(broadcast: ReturnType<typeof vi.fn>) {
     return broadcast.mock.calls.filter(([event]) => event === "agent");
   }
@@ -1440,6 +1447,73 @@ describe("agent event handler", () => {
     nowSpy.mockRestore();
   });
 
+  it("delivers a throttled delta when the window expires without another event", () => {
+    vi.useFakeTimers();
+    let now = 12_000;
+    const nowSpy = vi.spyOn(Date, "now").mockImplementation(() => now);
+    const { broadcast, chatRunState, handler } = createHarness();
+    registerNamedChatRun(chatRunState, "trailing");
+
+    emitAgentEvent(handler, "run-trailing", "assistant", { text: "Hello" });
+    now = 12_020;
+    emitAgentEvent(handler, "run-trailing", "assistant", { text: "Hello world" });
+
+    expect(chatDeltaTexts(broadcast)).toEqual(["Hello"]);
+    now = 12_150;
+    vi.advanceTimersByTime(130);
+
+    expect(chatDeltaTexts(broadcast)).toEqual(["Hello", " world"]);
+    expect(vi.getTimerCount()).toBe(0);
+    nowSpy.mockRestore();
+  });
+
+  it("cancels the trailing delta before the terminal frame", () => {
+    vi.useFakeTimers();
+    let now = 13_000;
+    const nowSpy = vi.spyOn(Date, "now").mockImplementation(() => now);
+    const { broadcast, chatRunState, handler } = createHarness();
+    registerNamedChatRun(chatRunState, "terminal-trailing");
+
+    emitAgentEvent(handler, "run-terminal-trailing", "assistant", { text: "Hello" });
+    now = 13_020;
+    emitAgentEvent(handler, "run-terminal-trailing", "assistant", { text: "Hello world" });
+    expect(vi.getTimerCount()).toBe(1);
+
+    emitLifecycleEnd(handler, "run-terminal-trailing");
+    expect(vi.getTimerCount()).toBe(0);
+    const statesAtTerminal = chatBroadcastCalls(broadcast).map(
+      ([, payload]) => (payload as { state?: string }).state,
+    );
+    expect(statesAtTerminal).toEqual(["delta", "delta", "final"]);
+
+    now = 13_500;
+    vi.advanceTimersByTime(1_000);
+    expect(
+      chatBroadcastCalls(broadcast).map(([, payload]) => (payload as { state?: string }).state),
+    ).toEqual(statesAtTerminal);
+    nowSpy.mockRestore();
+  });
+
+  it("cancels trailing deltas when gateway chat state is cleared", () => {
+    vi.useFakeTimers();
+    let now = 14_000;
+    const nowSpy = vi.spyOn(Date, "now").mockImplementation(() => now);
+    const { broadcast, chatRunState, handler } = createHarness();
+    registerNamedChatRun(chatRunState, "shutdown-trailing");
+
+    emitAgentEvent(handler, "run-shutdown-trailing", "assistant", { text: "Hello" });
+    now = 14_020;
+    emitAgentEvent(handler, "run-shutdown-trailing", "assistant", { text: "Hello world" });
+    expect(vi.getTimerCount()).toBe(1);
+
+    chatRunState.clear();
+    expect(vi.getTimerCount()).toBe(0);
+    now = 14_500;
+    vi.advanceTimersByTime(1_000);
+    expect(chatDeltaTexts(broadcast)).toEqual(["Hello"]);
+    nowSpy.mockRestore();
+  });
+
   it("does not emit a delta when a repeated assistant snapshot is unchanged", () => {
     let now = 11_250;
     const nowSpy = vi.spyOn(Date, "now").mockImplementation(() => now);

src/gateway/server-chat.ts

@@ -221,6 +221,7 @@ function normalizeHeartbeatChatFinalText(params: {
  * do not finalize a run before fallback or retry reuses the same runId.
  */
 const AGENT_LIFECYCLE_ERROR_RETRY_GRACE_MS = 15_000;
+const CHAT_DELTA_THROTTLE_MS = 150;
 
 export type ChatEventBroadcast = GatewayBroadcastFn;
 
@@ -359,6 +360,16 @@ type AgentEventHandler = ((event: AgentEventPayload) => void) & {
   dispose: () => void;
 };
 
+type InternalChatRunRecord = ReturnType<ChatRunState["getOrCreate"]> & {
+  pendingDeltaFlush?: { timer: NodeJS.Timeout; flush: () => void };
+};
+
+function internalChatRunRecord(
+  record: ReturnType<ChatRunState["getOrCreate"]>,
+): InternalChatRunRecord {
+  return record;
+}
+
 function roundedChatSendTimingMs(value: number): number {
   return Math.max(0, Math.round(value * 1000) / 1000);
 }
@@ -421,6 +432,16 @@ export function createAgentEventHandler({
 
   const agentTextThrottleStreams = ["assistant", "thinking"] as const;
 
+  const cancelPendingChatDeltaFlush = (clientRunId: string) => {
+    const record = chatRunState.runs.get(clientRunId);
+    const pending = record ? internalChatRunRecord(record).pendingDeltaFlush : undefined;
+    if (!pending || !record) {
+      return;
+    }
+    clearTimeout(pending.timer);
+    delete internalChatRunRecord(record).pendingDeltaFlush;
+  };
+
   const clearBufferedChatState = (clientRunId: string) => {
     chatRunState.clearRun(clientRunId);
   };
@@ -887,6 +908,89 @@ export function createAgentEventHandler({
     pendingTerminalLifecycleErrors.set(evt.runId, { timer, event: evt, opts });
   };
 
+  const broadcastChatDelta = (
+    sessionKey: string,
+    agentId: string | undefined,
+    clientRunId: string,
+    sourceRunId: string,
+    seq: number,
+    text: string,
+    opts?: { controlUiVisible?: boolean; firstAssistantTimingEntry?: ChatRunEntry },
+  ) => {
+    cancelPendingChatDeltaFlush(clientRunId);
+    const run = chatRunState.getOrCreate(clientRunId);
+    const broadcastDelta = resolveBroadcastDelta({
+      text,
+      previousBroadcastText: run.deltaLastBroadcastText,
+    });
+    if (!broadcastDelta) {
+      return;
+    }
+    const now = Date.now();
+    run.deltaSentAt = now;
+    run.deltaLastBroadcastText = text;
+    const spawnedBy = resolveSpawnedBy(sessionKey);
+    const payload = {
+      runId: clientRunId,
+      sessionKey,
+      ...(agentId ? { agentId } : {}),
+      ...(spawnedBy && { spawnedBy }),
+      seq,
+      state: "delta" as const,
+      deltaText: broadcastDelta.deltaText,
+      ...(broadcastDelta.replace ? { replace: true as const } : {}),
+      message: {
+        role: "assistant",
+        content: [{ type: "text", text }],
+        timestamp: now,
+      },
+    };
+    emitFirstAssistantChatSendTiming(
+      opts?.firstAssistantTimingEntry ?? chatRunState.registry.peek(sourceRunId),
+    );
+    sendChatPayload(sessionKey, payload, {
+      agentId,
+      controlUiVisible: opts?.controlUiVisible ?? true,
+      dropIfSlow: true,
+    });
+  };
+
+  const scheduleChatDeltaFlush = (
+    sessionKey: string,
+    agentId: string | undefined,
+    clientRunId: string,
+    sourceRunId: string,
+    seq: number,
+    delayMs: number,
+    controlUiVisible: boolean | undefined,
+  ) => {
+    const run = internalChatRunRecord(chatRunState.getOrCreate(clientRunId));
+    const flush = () => {
+      const projected = chatRunState.resolveBuffer(clientRunId);
+      if (projected.suppress || shouldHideHeartbeatChatOutput(clientRunId, sourceRunId)) {
+        return;
+      }
+      broadcastChatDelta(sessionKey, agentId, clientRunId, sourceRunId, seq, projected.text, {
+        controlUiVisible,
+      });
+    };
+    const existing = run.pendingDeltaFlush;
+    if (existing) {
+      existing.flush = flush;
+      return;
+    }
+    const timer = setSafeTimeout(() => {
+      const pending = run.pendingDeltaFlush;
+      if (!pending || pending.timer !== timer) {
+        return;
+      }
+      cancelPendingChatDeltaFlush(clientRunId);
+      pending.flush();
+    }, delayMs);
+    timer.unref?.();
+    run.pendingDeltaFlush = { timer, flush };
+  };
+
   const emitChatDelta = (
     sessionKey: string,
     agentId: string | undefined,
@@ -910,8 +1014,17 @@ export function createAgentEventHandler({
     const now = Date.now();
     run.rawBuffer = mergedRawText;
     run.bufferUpdatedAt = now;
-    const last = run.deltaSentAt ?? 0;
-    if (now - last < 150) {
+    const waitedMs = now - (run.deltaSentAt ?? 0);
+    if (waitedMs < CHAT_DELTA_THROTTLE_MS) {
+      scheduleChatDeltaFlush(
+        sessionKey,
+        agentId,
+        clientRunId,
+        sourceRunId,
+        seq,
+        CHAT_DELTA_THROTTLE_MS - waitedMs,
+        opts?.controlUiVisible,
+      );
       return;
     }
     const projected = chatRunState.resolveBuffer(clientRunId);
@@ -919,38 +1032,7 @@ export function createAgentEventHandler({
     if (projected.suppress || shouldHideHeartbeatChatOutput(clientRunId, sourceRunId)) {
       return;
     }
-    const broadcastDelta = resolveBroadcastDelta({
-      text: mergedText,
-      previousBroadcastText: run.deltaLastBroadcastText,
-    });
-    if (!broadcastDelta) {
-      return;
-    }
-    run.deltaSentAt = now;
-    run.deltaLastBroadcastLen = mergedText.length;
-    run.deltaLastBroadcastText = mergedText;
-    const spawnedBy = resolveSpawnedBy(sessionKey);
-    const payload = {
-      runId: clientRunId,
-      sessionKey,
-      ...(agentId ? { agentId } : {}),
-      ...(spawnedBy && { spawnedBy }),
-      seq,
-      state: "delta" as const,
-      deltaText: broadcastDelta.deltaText,
-      ...(broadcastDelta.replace ? { replace: true as const } : {}),
-      message: {
-        role: "assistant",
-        content: [{ type: "text", text: mergedText }],
-        timestamp: now,
-      },
-    };
-    emitFirstAssistantChatSendTiming(chatRunState.registry.peek(sourceRunId));
-    sendChatPayload(sessionKey, payload, {
-      agentId,
-      controlUiVisible: opts?.controlUiVisible ?? true,
-      dropIfSlow: true,
-    });
+    broadcastChatDelta(sessionKey, agentId, clientRunId, sourceRunId, seq, mergedText, opts);
   };
 
   const resolveBufferedChatTextState = (
@@ -981,6 +1063,7 @@ export function createAgentEventHandler({
     seq: number,
     opts?: { controlUiVisible?: boolean; firstAssistantTimingEntry?: ChatRunEntry },
   ) => {
+    cancelPendingChatDeltaFlush(clientRunId);
     const { text, shouldSuppressSilent } = resolveBufferedChatTextState(clientRunId, sourceRunId, {
       suppressLeadFragments: true,
     });
@@ -992,42 +1075,7 @@ export function createAgentEventHandler({
       return;
     }
 
-    const now = Date.now();
-    const run = chatRunState.getOrCreate(clientRunId);
-    const delta = resolveBroadcastDelta({
-      text,
-      previousBroadcastText: run.deltaLastBroadcastText,
-    });
-    if (!delta) {
-      return;
-    }
-    const spawnedBy = resolveSpawnedBy(sessionKey);
-    const flushPayload = {
-      runId: clientRunId,
-      sessionKey,
-      ...(agentId ? { agentId } : {}),
-      ...(spawnedBy && { spawnedBy }),
-      seq,
-      state: "delta" as const,
-      deltaText: delta.deltaText,
-      ...(delta.replace ? { replace: true as const } : {}),
-      message: {
-        role: "assistant",
-        content: [{ type: "text", text }],
-        timestamp: now,
-      },
-    };
-    emitFirstAssistantChatSendTiming(
-      opts?.firstAssistantTimingEntry ?? chatRunState.registry.peek(sourceRunId),
-    );
-    sendChatPayload(sessionKey, flushPayload, {
-      agentId,
-      controlUiVisible: opts?.controlUiVisible ?? true,
-      dropIfSlow: true,
-    });
-    run.deltaLastBroadcastLen = text.length;
-    run.deltaLastBroadcastText = text;
-    run.deltaSentAt = now;
+    broadcastChatDelta(sessionKey, agentId, clientRunId, sourceRunId, seq, text, opts);
   };
 
   const sendChatPayload = (

src/gateway/server-node-events.test.ts

@@ -1324,8 +1324,7 @@ describe("voice transcript events", () => {
     const [runId, runMetadata] = mockCall(addChatRun) ?? [];
     expect(runId).toBe(optsRecord.runId);
     const clientRunId = (runMetadata as { clientRunId?: unknown } | undefined)?.clientRunId;
-    expect(typeof clientRunId).toBe("string");
-    expect(clientRunId).toMatch(/^voice-/);
+    expect(clientRunId).toBe(runId);
   });
 
   it("does not block agent dispatch when session-store touch fails", async () => {

src/gateway/server-node-events.ts

@@ -607,11 +607,11 @@ export const handleNodeEvent = async (
             isConnectionCurrent: opts?.isConnectionCurrent,
           });
 
-          // Ensure chat UI clients refresh when this run completes (even though it wasn't started via chat.send).
-          // This maps agent bus events (keyed by per-turn runId) to chat events (keyed by clientRunId).
+          // Voice now has a unique per-turn run id, so it is also the stable
+          // client identity for chat streaming and abort lifecycle ownership.
           ctx.addChatRun(runId, {
             sessionKey: canonicalKey,
-            clientRunId: `voice-${randomUUID()}`,
+            clientRunId: runId,
           });
         },
       });

test/e2e/qa-lab/runtime/agent-session-streaming.e2e.test.ts

@@ -10,7 +10,7 @@ import {
 
 const TEST_TIMEOUT_MS = 120_000;
 const REQUEST_TIMEOUT_MS = 20_000;
-const STREAM_INTERVAL_MS = 225;
+const STREAM_INTERVAL_MS = 20;
 const MODEL_REF = "mock-openai/gpt-5.6-luna";
 const SESSION_KEY = "agent:qa:qa:session-streaming";
 const IDEMPOTENCY_KEY = "qa-session-streaming";
@@ -27,6 +27,12 @@ type GatewayEvent = {
   event: string;
   payload?: unknown;
 };
+type ChatEventPayload = {
+  runId?: string;
+  sessionKey?: string;
+  state?: string;
+  deltaText?: string;
+};
 type AgentEvent = {
   runId?: string;
   sessionKey?: string;
@@ -41,6 +47,14 @@ type AgentEvent = {
 
 const cleanups: Array<() => Promise<void>> = [];
 
+function createDeferred() {
+  let resolve = () => {};
+  const promise = new Promise<void>((settle) => {
+    resolve = settle;
+  });
+  return { promise, resolve };
+}
+
 afterEach(async () => {
   const errors: unknown[] = [];
   for (const cleanup of cleanups.splice(0).toReversed()) {
@@ -62,7 +76,11 @@ function writeEvent(response: ServerResponse, event: unknown): void {
   response.write(`data: ${JSON.stringify(event)}\n\n`);
 }
 
-async function writeStreamingResponse(response: ServerResponse): Promise<void> {
+async function writeStreamingResponse(
+  response: ServerResponse,
+  deltasSent: ReturnType<typeof createDeferred>,
+  terminalRelease: ReturnType<typeof createDeferred>,
+): Promise<void> {
   const message = {
     type: "message",
     id: "qa-session-streaming-message",
@@ -91,6 +109,8 @@ async function writeStreamingResponse(response: ServerResponse): Promise<void> {
     });
     await delay(STREAM_INTERVAL_MS);
   }
+  deltasSent.resolve();
+  await terminalRelease.promise;
   writeEvent(response, {
     type: "response.output_text.done",
     item_id: message.id,
@@ -114,6 +134,13 @@ async function writeStreamingResponse(response: ServerResponse): Promise<void> {
 async function startStreamingProvider() {
   const providerRequests: Array<Record<string, unknown>> = [];
   const transportRequests: string[] = [];
+  const deltasSent = createDeferred();
+  const terminalRelease = createDeferred();
+  let terminalReleased = false;
+  const releaseTerminal = () => {
+    terminalReleased = true;
+    terminalRelease.resolve();
+  };
   const server = createServer((request, response) => {
     void (async () => {
       if (request.method === "GET" && request.url === "/v1/models") {
@@ -133,7 +160,7 @@ async function startStreamingProvider() {
         providerRequests.push(
           JSON.parse(Buffer.concat(chunks).toString("utf8")) as Record<string, unknown>,
         );
-        await writeStreamingResponse(response);
+        await writeStreamingResponse(response, deltasSent, terminalRelease);
         return;
       }
       transportRequests.push(`${request.method ?? "UNKNOWN"} ${request.url ?? ""}`);
@@ -153,9 +180,13 @@ async function startStreamingProvider() {
   }
   return {
     baseUrl: `http://127.0.0.1:${address.port}`,
+    deltasSent: deltasSent.promise,
+    isTerminalReleased: () => terminalReleased,
+    releaseTerminal,
     providerRequests,
     transportRequests,
     stop: async () => {
+      releaseTerminal();
       server.closeAllConnections();
       await new Promise<void>((resolve, reject) => {
         server.close((error) => (error ? reject(error) : resolve()));
@@ -216,6 +247,12 @@ function asAgentEvent(event: GatewayEvent): AgentEvent | undefined {
     : undefined;
 }
 
+function asChatEvent(event: GatewayEvent): ChatEventPayload | undefined {
+  return event.event === "chat" && event.payload && typeof event.payload === "object"
+    ? (event.payload as ChatEventPayload)
+    : undefined;
+}
+
 function messageRole(message: unknown): string | undefined {
   const role = message && typeof message === "object" ? (message as { role?: unknown }).role : null;
   return typeof role === "string" ? role : undefined;
@@ -275,6 +312,7 @@ describe("agent session streaming", () => {
       const gatewayEvents: GatewayEvent[] = [];
       const client = await connectOperator(gateway, gatewayEvents);
       cleanups.push(() => client.stopAndWait({ timeoutMs: 1_000 }));
+      await client.request("sessions.messages.subscribe", { key: SESSION_KEY });
       const accepted = await client.request<AgentResult>("agent", {
         sessionKey: SESSION_KEY,
         message: REQUEST_MESSAGE,
@@ -286,6 +324,21 @@ describe("agent session streaming", () => {
         runId: IDEMPOTENCY_KEY,
       });
 
+      await provider.deltasSent;
+      await vi.waitFor(
+        () => {
+          expect(provider.isTerminalReleased()).toBe(false);
+          const streamedChatText = gatewayEvents
+            .map(asChatEvent)
+            .filter((event) => event?.runId === IDEMPOTENCY_KEY && event.state === "delta")
+            .map((event) => event?.deltaText ?? "")
+            .join("");
+          expect(streamedChatText).toBe(TERMINAL_TEXT);
+        },
+        { interval: 20, timeout: REQUEST_TIMEOUT_MS },
+      );
+      provider.releaseTerminal();
+
       const terminal = await client.request<AgentResult>(
         "agent.wait",
         { runId: IDEMPOTENCY_KEY, timeoutMs: 30_000 },
@@ -345,6 +398,32 @@ describe("agent session streaming", () => {
       });
       expect(terminalEvents[0]?.seq).toBeGreaterThan(deltaSeqs.at(-1) ?? 0);
 
+      await vi.waitFor(
+        () => {
+          const runChatEvents = gatewayEvents
+            .map(asChatEvent)
+            .filter((event) => event?.runId === IDEMPOTENCY_KEY);
+          expect(runChatEvents.filter((event) => event?.state === "final")).toHaveLength(1);
+        },
+        { interval: 20, timeout: REQUEST_TIMEOUT_MS },
+      );
+      const runChatEventsAtTerminal = gatewayEvents
+        .map(asChatEvent)
+        .filter((event) => event?.runId === IDEMPOTENCY_KEY);
+      const finalIndex = runChatEventsAtTerminal.findIndex((event) => event?.state === "final");
+      expect(finalIndex).toBeGreaterThan(-1);
+      expect(
+        runChatEventsAtTerminal.slice(finalIndex + 1).some((event) => event?.state === "delta"),
+      ).toBe(false);
+      await delay(250);
+      expect(
+        gatewayEvents
+          .map(asChatEvent)
+          .filter((event) => event?.runId === IDEMPOTENCY_KEY)
+          .slice(finalIndex + 1)
+          .some((event) => event?.state === "delta"),
+      ).toBe(false);
+
       const streamedText = assistantDeltas.map((event) => event.data?.delta ?? "").join("");
       expect(streamedText).toBe(TERMINAL_TEXT);