feat(claude): merge client anthropic-beta flags and forward rate-limit headers

open-sse/handlers/chatCore/streamingHandler.js

@@ -9,6 +9,7 @@ import { buildStreamErrorBytes } from "../../utils/streamHelpers.js";
 import { buildRequestDetail, extractRequestConfig, saveUsageStats, formatDoneLine } from "./requestDetail.js";
 import { saveRequestDetail } from "@/lib/usageDb.js";
 import { SSE_HEADERS_CORS as SSE_HEADERS } from "../../utils/sseConstants.js";
+import { upstreamResponseHeaders } from "../../utils/upstreamHeaders.js";
 
 // Codex returns Responses API SSE → which client format to translate INTO, by request sourceFormat.
 // Gemini-family all map to ANTIGRAVITY decoder; unknown sources fall back to OPENAI.
@@ -109,7 +110,7 @@ export async function handleStreamingResponse({ providerResponse, provider, mode
 
   return {
     success: true,
-    response: new Response(transformedBody, { headers: SSE_HEADERS })
+    response: new Response(transformedBody, { headers: { ...SSE_HEADERS, ...upstreamResponseHeaders(providerResponse.headers) } })
   };
 }