feat: Add support for OpenAI Responses endpoint and enhance proxy retry logic

- Updated proxyRetryPolicy to retry on all 4xx and 5xx status codes.
- Introduced 'responses' target format in TestChatRequestPayload.
- Implemented extractResponsesContent function to handle responses format in ModelTester.
- Enhanced ModelTester to support responses target format and display appropriate labels.
- Updated ProxyLogs to extract and display upstream paths from error messages.
- Added tests to ensure responses target format is preserved during payload sync.
- Created responses proxy route to handle requests to the new OpenAI Responses endpoint.
- Updated upstreamEndpoint logic to include responses endpoint handling.
- Added modelService tests to validate token route rebuilding logic.

src/web/pages/helpers/modelTesterSession.test.ts

@@ -199,6 +199,17 @@ describe('modelTesterSession', () => {
     expect(syncedJson.messages).toEqual([{ role: 'user', content: 'new' }]);
   });
 
+  it('keeps responses target format in custom payload sync', () => {
+    const synced = syncMessagesToCustomRequestBody(
+      '{"model":"gpt-5.2","targetFormat":"responses"}',
+      [{ id: '1', role: 'user', content: 'hello', createAt: 1 }],
+      { ...DEFAULT_INPUTS, model: 'gpt-5.2', targetFormat: 'openai' },
+    );
+
+    const syncedJson = JSON.parse(synced);
+    expect(syncedJson.targetFormat).toBe('responses');
+  });
+
   it('merges marketplace models with exact enabled route models for tester options', () => {
     const modelNames = collectModelTesterModelNames(
       {

src/web/pages/helpers/modelTesterSession.ts

@@ -14,7 +14,7 @@ export const DEBUG_TABS = {
 type MessageStatus = typeof MESSAGE_STATUS[keyof typeof MESSAGE_STATUS];
 export type DebugTab = typeof DEBUG_TABS[keyof typeof DEBUG_TABS];
 type ChatRole = 'user' | 'assistant' | 'system';
-export type TestTargetFormat = 'openai' | 'claude';
+export type TestTargetFormat = 'openai' | 'claude' | 'responses';
 
 export type ChatMessage = {
   id: string;
@@ -256,7 +256,11 @@ const parseInputs = (value: unknown, fallbackModel = ''): ModelTesterInputs => {
 
   return {
     model,
-    targetFormat: value.targetFormat === 'claude' ? 'claude' : DEFAULT_INPUTS.targetFormat,
+    targetFormat: value.targetFormat === 'claude'
+      ? 'claude'
+      : value.targetFormat === 'responses'
+        ? 'responses'
+        : DEFAULT_INPUTS.targetFormat,
     temperature: toFiniteNumber(value.temperature, DEFAULT_INPUTS.temperature),
     top_p: toFiniteNumber(value.top_p, DEFAULT_INPUTS.top_p),
     max_tokens: toFiniteNumber(value.max_tokens, DEFAULT_INPUTS.max_tokens),
@@ -298,7 +302,7 @@ const parsePendingPayload = (value: unknown): TestChatPayload | null => {
     messages: payloadMessages,
   };
 
-  if (value.targetFormat === 'claude' || value.targetFormat === 'openai') {
+  if (value.targetFormat === 'claude' || value.targetFormat === 'openai' || value.targetFormat === 'responses') {
     payload.targetFormat = value.targetFormat;
   }
   if (typeof value.stream === 'boolean') payload.stream = value.stream;
@@ -385,7 +389,11 @@ const buildFallbackInputsFromLegacy = (value: Record<string, unknown>): ModelTes
   const inputs = parseInputs(value.inputs, legacyModel);
 
   if (!value.inputs) {
-    inputs.targetFormat = value.targetFormat === 'claude' ? 'claude' : inputs.targetFormat;
+    inputs.targetFormat = value.targetFormat === 'claude'
+      ? 'claude'
+      : value.targetFormat === 'responses'
+        ? 'responses'
+        : inputs.targetFormat;
     inputs.temperature = toFiniteNumber(value.temperature, inputs.temperature);
   }
 
@@ -511,7 +519,11 @@ export const syncMessagesToCustomRequestBody = (
   payload.model = typeof payload.model === 'string' && payload.model.trim().length > 0
     ? payload.model
     : inputs.model;
-  payload.targetFormat = payload.targetFormat === 'claude' ? 'claude' : inputs.targetFormat;
+  payload.targetFormat = payload.targetFormat === 'claude'
+    ? 'claude'
+    : payload.targetFormat === 'responses'
+      ? 'responses'
+      : inputs.targetFormat;
   payload.stream = payload.stream !== undefined ? payload.stream : inputs.stream;
   payload.messages = toApiMessages(messages);