From 13a871bdbac9b3ef96e05afefd5bb613c7ad6af8 Mon Sep 17 00:00:00 2001
From: Hayden <hayden@openai.com>
Date: Mon, 6 Jul 2026 11:43:48 -0700
Subject: [PATCH 1/2] emit stream finalization errors

Resolves #553
---
 src/lib/EventStream.ts                 | 11 ++++---
 tests/lib/ChatCompletionStream.test.ts | 45 ++++++++++++++++++++++++++
 2 files changed, 52 insertions(+), 4 deletions(-)

diff --git a/src/lib/EventStream.ts b/src/lib/EventStream.ts
index db45ab348..40878d2ce 100644
--- a/src/lib/EventStream.ts
+++ b/src/lib/EventStream.ts
@@ -44,10 +44,13 @@ export class EventStream<EventTypes extends BaseEvents> {
     // Unfortunately if we call `executor()` immediately we get runtime errors about
     // references to `this` before the `super()` constructor call returns.
     setTimeout(() => {
-      executor().then(() => {
-        this._emitFinal();
-        this._emit('end');
-      }, this.#handleError.bind(this));
+      Promise.resolve()
+        .then(executor)
+        .then(() => {
+          this._emitFinal();
+          this._emit('end');
+        })
+        .catch(this.#handleError.bind(this));
     }, 0);
   }
 
diff --git a/tests/lib/ChatCompletionStream.test.ts b/tests/lib/ChatCompletionStream.test.ts
index a7236903b..758c7f296 100644
--- a/tests/lib/ChatCompletionStream.test.ts
+++ b/tests/lib/ChatCompletionStream.test.ts
@@ -8,6 +8,51 @@ import { makeStreamSnapshotRequest } from '../utils/mock-snapshots';
 jest.setTimeout(1000 * 30);
 
 describe('.stream()', () => {
+  it('emits finalization failures as errors', async () => {
+    const chunk: OpenAI.Chat.ChatCompletionChunk = {
+      id: 'chatcmpl-test',
+      object: 'chat.completion.chunk',
+      created: 1,
+      model: 'gpt-test',
+      choices: [
+        {
+          index: 0,
+          delta: { role: 'user', content: 'hello' },
+          finish_reason: 'stop',
+          logprobs: null,
+        },
+      ],
+    };
+
+    const client = {
+      chat: {
+        completions: {
+          create: jest.fn(async () => ({
+            controller: new AbortController(),
+            async *[Symbol.asyncIterator]() {
+              yield chunk;
+            },
+          })),
+        },
+      },
+    } as unknown as OpenAI;
+
+    const stream = ChatCompletionStream.createChatCompletion(client, {
+      model: 'gpt-test',
+      messages: [{ role: 'user', content: 'Say hello' }],
+    });
+    const errors: Error[] = [];
+    stream.on('error', (error) => errors.push(error));
+
+    await expect(stream.done()).rejects.toThrow(
+      'stream ended without producing a ChatCompletionMessage with role=assistant',
+    );
+    expect(errors).toHaveLength(1);
+    expect(errors[0]?.message).toBe(
+      'stream ended without producing a ChatCompletionMessage with role=assistant',
+    );
+  });
+
   it('removes the caller abort listener after the stream finishes', async () => {
     const callerController = new AbortController();
     const addEventListenerSpy = jest.spyOn(callerController.signal, 'addEventListener');

From 1e9094e8c3d6707d825f8b2b16b2ad552bee0c12 Mon Sep 17 00:00:00 2001
From: Hayden <hayden@openai.com>
Date: Mon, 6 Jul 2026 12:19:07 -0700
Subject: [PATCH 2/2] fix: preserve end listener failures

---
 src/lib/EventStream.ts | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/src/lib/EventStream.ts b/src/lib/EventStream.ts
index 40878d2ce..2bc07f2cd 100644
--- a/src/lib/EventStream.ts
+++ b/src/lib/EventStream.ts
@@ -47,10 +47,14 @@ export class EventStream<EventTypes extends BaseEvents> {
       Promise.resolve()
         .then(executor)
         .then(() => {
-          this._emitFinal();
+          try {
+            this._emitFinal();
+          } catch (error) {
+            this.#handleError(error);
+            return;
+          }
           this._emit('end');
-        })
-        .catch(this.#handleError.bind(this));
+        }, this.#handleError.bind(this));
     }, 0);
   }