fix: decode zstd responses while restoring claude encoding

src/server/routes/proxy/chat.count-tokens.test.ts

@@ -145,7 +145,7 @@ describe('claude count_tokens proxy route', () => {
     expect(targetUrl).toBe('https://api.anthropic.com/v1/messages/count_tokens?beta=true');
     expect(options.headers['anthropic-version']).toBe('2023-06-01');
     expect(options.headers['anthropic-beta']).toContain('claude-code-20250219');
-    expect(options.headers['Accept-Encoding']).toBe('identity');
+    expect(options.headers['Accept-Encoding']).toBe('gzip, deflate, br, zstd');
 
     const forwardedBody = JSON.parse(String(options.body));
     expect(forwardedBody.model).toBe('claude-opus-4-6');

src/server/routes/proxy/endpointFlow.ts

@@ -1,4 +1,5 @@
 import { fetch } from 'undici';
+import { readRuntimeResponseText } from '../../proxy-core/executors/types.js';
 import { withSiteProxyRequestInit } from '../../services/siteProxy.js';
 import { summarizeUpstreamError } from './upstreamError.js';
 import type { UpstreamEndpoint } from './upstreamEndpoint.js';
@@ -114,7 +115,7 @@ export async function executeEndpointFlow(input: ExecuteEndpointFlowInput): Prom
       };
     }
 
-    let rawErrText = await response.text().catch(() => 'unknown error');
+    let rawErrText = await readRuntimeResponseText(response).catch(() => 'unknown error');
     const baseContext: EndpointAttemptContext = {
       endpointIndex,
       endpointCount,

src/server/routes/proxy/upstreamEndpoint.test.ts

@@ -864,7 +864,7 @@ describe('buildUpstreamEndpointRequest', () => {
     expect(request.headers['User-Agent']).toBe('claude-cli/2.1.63 (external, cli)');
     expect(request.headers.Connection).toBe('keep-alive');
     expect(request.headers.Accept).toBe('text/event-stream');
-    expect(request.headers['Accept-Encoding']).toBe('identity');
+    expect(request.headers['Accept-Encoding']).toBe('gzip, deflate, br, zstd');
   });
 
   it('uses claude-code beta headers and uncompressed non-stream responses for claude upstream requests', () => {
@@ -887,7 +887,7 @@ describe('buildUpstreamEndpointRequest', () => {
     expect(request.headers['anthropic-beta']).toContain('oauth-2025-04-20');
     expect(request.headers['anthropic-beta']).toContain('context-management-2025-06-27');
     expect(request.headers.Accept).toBe('application/json');
-    expect(request.headers['Accept-Encoding']).toBe('identity');
+    expect(request.headers['Accept-Encoding']).toBe('gzip, deflate, br, zstd');
   });
 
   it('converts system roles to developer in native codex responses bodies', () => {

src/server/routes/proxy/upstreamEndpoint.ts

@@ -443,7 +443,7 @@ function buildClaudeRuntimeHeaders(input: {
     'User-Agent': getInputHeader(input.claudeHeaders, 'user-agent') || CLAUDE_DEFAULT_USER_AGENT,
     Connection: 'keep-alive',
     Accept: input.stream ? 'text/event-stream' : 'application/json',
-    'Accept-Encoding': 'identity',
+    'Accept-Encoding': 'gzip, deflate, br, zstd',
   };
   if (input.isClaudeOauthUpstream) {
     headers.Authorization = `Bearer ${input.tokenValue}`;