fix: route fun codex through responses api (#815)

tests/shared/provider-presets.test.ts

@@ -6,6 +6,7 @@ import {
 } from '../../packages/server/src/shared/providers'
 
 const OPENAI_CODEX_PROVIDER = 'openai-codex'
+const FUN_CODEX_PROVIDER = 'fun-codex'
 const GPT_5_5_MODEL = 'gpt-5.5'
 
 function modelsForProvider(providerPresets: Array<{ value: string; models: string[] }>, provider: string): string[] {
@@ -15,6 +16,11 @@ function modelsForProvider(providerPresets: Array<{ value: string; models: strin
 }
 
 describe('provider presets', () => {
+  it('routes apikey.fun Codex through the Responses transport', () => {
+    const preset = SERVER_PROVIDER_PRESETS.find((candidate) => candidate.value === FUN_CODEX_PROVIDER)
+    expect(preset?.api_mode).toBe('codex_responses')
+  })
+
   it('lists GPT-5.5 for OpenAI Codex', () => {
     expect(modelsForProvider(SERVER_PROVIDER_PRESETS, OPENAI_CODEX_PROVIDER)).toContain(GPT_5_5_MODEL)
   })