fix(openai): strip unsupported ChatGPT prompt cache retention options while preserving prompt cache keys

test/test.openai-auth.node.ts

@@ -203,6 +203,12 @@ tap.test('getModel uses ChatGPT Codex backend for OpenAI ChatGPT auth', async ()
       model,
       system: 'system prompt',
       prompt: 'hello',
+      providerOptions: {
+        openai: {
+          promptCacheKey: 'session-1',
+          promptCacheRetention: 'in_memory',
+        },
+      },
     });
 
     expect(capturedRequest?.url).toEqual('https://chatgpt.com/backend-api/codex/responses');
@@ -214,6 +220,8 @@ tap.test('getModel uses ChatGPT Codex backend for OpenAI ChatGPT auth', async ()
     expect(capturedBody.input).toEqual([
       { role: 'user', content: [{ type: 'input_text', text: 'hello' }] },
     ]);
+    expect(capturedBody.prompt_cache_key).toEqual('session-1');
+    expect(capturedBody.prompt_cache_retention).toEqual(undefined);
   } finally {
     globalThis.fetch = originalFetch;
   }