support openai response format through config

pkg/config/config.go

@@ -188,6 +188,7 @@ type ProviderConfig struct {
 	Proxy       string `json:"proxy,omitempty" env:"PICOCLAW_PROVIDERS_{{.Name}}_PROXY"`
 	AuthMethod  string `json:"auth_method,omitempty" env:"PICOCLAW_PROVIDERS_{{.Name}}_AUTH_METHOD"`
 	ConnectMode string `json:"connect_mode,omitempty" env:"PICOCLAW_PROVIDERS_{{.Name}}_CONNECT_MODE"` //only for Github Copilot, `stdio` or `grpc`
+	APIFormat   string `json:"api_format,omitempty" env:"PICOCLAW_PROVIDERS_{{.Name}}_API_FORMAT"`     // "responses" to use OpenAI Responses API
 }
 
 type GatewayConfig struct {

pkg/providers/codex_provider.go

@@ -26,8 +26,15 @@ type CodexProvider struct {
 const defaultCodexInstructions = "You are Codex, a coding assistant."
 
 func NewCodexProvider(token, accountID string) *CodexProvider {
+	return NewCodexProviderWithBase(token, accountID, "https://chatgpt.com/backend-api/codex")
+}
+
+func NewCodexProviderWithBase(token, accountID, baseURL string) *CodexProvider {
+	if baseURL == "" {
+		baseURL = "https://chatgpt.com/backend-api/codex"
+	}
 	opts := []option.RequestOption{
-		option.WithBaseURL("https://chatgpt.com/backend-api/codex"),
+		option.WithBaseURL(baseURL),
 		option.WithAPIKey(token),
 		option.WithHeader("originator", "codex_cli_rs"),
 		option.WithHeader("OpenAI-Beta", "responses=experimental"),

pkg/providers/http_provider.go

@@ -246,6 +246,13 @@ func CreateProvider(cfg *config.Config) (LLMProvider, error) {
 				if cfg.Providers.OpenAI.AuthMethod == "oauth" || cfg.Providers.OpenAI.AuthMethod == "token" {
 					return createCodexAuthProvider()
 				}
+				if cfg.Providers.OpenAI.APIFormat == "responses" {
+					base := cfg.Providers.OpenAI.APIBase
+					if base == "" {
+						base = "https://api.openai.com/v1"
+					}
+					return NewCodexProviderWithBase(cfg.Providers.OpenAI.APIKey, "", base), nil
+				}
 				apiKey = cfg.Providers.OpenAI.APIKey
 				apiBase = cfg.Providers.OpenAI.APIBase
 				if apiBase == "" {