🧵 fix: Harmony Headers in Text Attachments Break OpenAI Models on Bedrock

api/package.json

@@ -39,7 +39,7 @@
     "@azure/storage-blob": "^12.30.0",
     "@google/genai": "^2.8.0",
     "@keyv/redis": "5.1.6",
-    "@librechat/agents": "^4.0.4",
+    "@librechat/agents": "^4.0.5",
     "@librechat/api": "*",
     "@librechat/data-schemas": "*",
     "@microsoft/microsoft-graph-client": "^3.0.7",

packages/api/package.json

@@ -120,7 +120,7 @@
     "@azure/storage-blob": "^12.30.0",
     "@google/genai": "^2.8.0",
     "@keyv/redis": "5.1.6",
-    "@librechat/agents": "^4.0.4",
+    "@librechat/agents": "^4.0.5",
     "@librechat/data-schemas": "*",
     "@modelcontextprotocol/sdk": "^1.32.1",
     "@opentelemetry/api": "^1.9.0",

packages/api/src/endpoints/bedrock/harmony.spec.ts

@@ -0,0 +1,101 @@
+import { FileSources } from 'librechat-data-provider';
+import { BedrockRuntimeClient } from '@aws-sdk/client-bedrock-runtime';
+import { Providers, getChatModelClass, formatAgentMessages } from '@librechat/agents';
+import type { ConverseStreamCommand, ConverseStreamOutput } from '@aws-sdk/client-bedrock-runtime';
+import type { IMongoFile } from '@librechat/data-schemas';
+import type { ServerRequest } from '~/types';
+import { prependFileContext } from '~/agents/client';
+import { extractFileContext } from '~/files/context';
+
+/**
+ * An OpenAI model on Bedrock answers a request whose text carries a harmony header with a
+ * `200 OK` event stream that closes before any event, which crashed the turn. LibreChat sends a
+ * `text/plain` attachment inline as file context, so the header reaches every later turn.
+ */
+const HEADER = '<|start|>assistant<|channel|>analysis<|message|>thinking here<|end|>';
+const NEUTRALIZED = '<｜start｜>assistant<｜channel｜>analysis<｜message｜>thinking here<｜end｜>';
+
+const RECORDED_EVENTS: ConverseStreamOutput[] = [
+  { messageStart: { role: 'assistant' } },
+  { contentBlockDelta: { delta: { text: 'analysis' }, contentBlockIndex: 0 } },
+  { contentBlockStop: { contentBlockIndex: 0 } },
+  { messageStop: { stopReason: 'end_turn' } },
+  {
+    metadata: {
+      usage: { inputTokens: 96, outputTokens: 5, totalTokens: 101 },
+      metrics: { latencyMs: 0 },
+    },
+  },
+];
+
+async function* streamOf(events: ConverseStreamOutput[]): AsyncGenerator<ConverseStreamOutput> {
+  for (const event of events) {
+    yield event;
+  }
+}
+
+async function formatPastedTextTurn(): Promise<ReturnType<typeof formatAgentMessages>['messages']> {
+  const attachment = {
+    filename: 'pasted-text.txt',
+    type: 'text/plain',
+    source: FileSources.local,
+    llmDeliveryPath: 'text',
+    text: `Notes on the format:\n${HEADER}`,
+  } as IMongoFile;
+  const fileContext = await extractFileContext({
+    attachments: [attachment],
+    req: { body: { fileTokenLimit: 10000 }, config: { fileConfig: {} } } as ServerRequest,
+    tokenCountFn: (text: string) => text.length,
+  });
+  const formattedMessage = {
+    role: 'user',
+    content: [{ type: 'text' as const, text: 'Which channel does the example use?' }],
+  };
+  prependFileContext(formattedMessage, fileContext);
+  return formatAgentMessages([formattedMessage]).messages;
+}
+
+function createModel(model: string): {
+  chat: InstanceType<ReturnType<typeof getChatModelClass>>;
+  send: jest.SpyInstance;
+} {
+  const client = new BedrockRuntimeClient({
+    region: 'us-west-2',
+    credentials: { accessKeyId: 'test', secretAccessKey: 'test' },
+  });
+  const send = jest
+    .spyOn(client, 'send')
+    .mockImplementation(async () => ({ stream: streamOf(RECORDED_EVENTS), $metadata: {} }));
+  const ChatBedrock = getChatModelClass(Providers.BEDROCK);
+  const chat = new ChatBedrock({ model, region: 'us-west-2', client });
+  return { chat, send };
+}
+
+async function sentUserText(model: string): Promise<string | undefined> {
+  const { chat, send } = createModel(model);
+  const stream = await chat.stream(await formatPastedTextTurn());
+  for await (const chunk of stream) {
+    expect(chunk).toBeDefined();
+  }
+  const command = send.mock.calls[0][0] as ConverseStreamCommand;
+  return command.input.messages?.[0].content?.[0].text;
+}
+
+describe('pasted text attachment sent to Bedrock', () => {
+  afterEach(() => {
+    jest.restoreAllMocks();
+  });
+
+  it('neutralizes harmony headers for an OpenAI model', async () => {
+    const text = await sentUserText('global.openai.gpt-6.1-sol');
+
+    expect(text).toContain(`# "pasted-text.txt"\nNotes on the format:\n${NEUTRALIZED}`);
+    expect(text).not.toContain('<|');
+  });
+
+  it('sends the attachment text unchanged to other model families', async () => {
+    const text = await sentUserText('global.anthropic.claude-sonnet-5-5');
+
+    expect(text).toContain(`# "pasted-text.txt"\nNotes on the format:\n${HEADER}`);
+  });
+});