Add model-native search (prefer_native) for OpenAI/Codex (#1618)

* config: add prefer_native and NativeSearchCapable for model-native search

* providers: implement native web search for OpenAI and Codex

* agent: use provider-native search when prefer_native and supported

* tests: add coverage for model-native search

* fix: Golang lint errors

* fix: update the code based on the review

* fix: update codex_provider_test

pkg/config/config.go

@@ -693,6 +693,12 @@ type WebToolsConfig struct {
 	Perplexity PerplexityConfig `                                json:"perplexity"`
 	SearXNG    SearXNGConfig    `                                json:"searxng"`
 	GLMSearch  GLMSearchConfig  `                                json:"glm_search"`
+	// PreferNative controls whether to use provider-native web search when
+	// the active LLM supports it (e.g. OpenAI web_search_preview). When true,
+	// the client-side web_search tool is hidden to avoid duplicate search surfaces,
+	// and the provider's built-in search is used instead. Falls back to client-side
+	// search when the provider does not support native search.
+	PreferNative bool `json:"prefer_native" env:"PICOCLAW_TOOLS_WEB_PREFER_NATIVE"`
 	// Proxy is an optional proxy URL for web tools (http/https/socks5/socks5h).
 	// For authenticated proxies, prefer HTTP_PROXY/HTTPS_PROXY env vars instead of embedding credentials in config.
 	Proxy                string              `json:"proxy,omitempty"                  env:"PICOCLAW_TOOLS_WEB_PROXY"`

pkg/config/config_test.go

@@ -401,6 +401,45 @@ func TestDefaultConfig_OpenAIWebSearchEnabled(t *testing.T) {
 	}
 }
 
+func TestDefaultConfig_WebPreferNativeEnabled(t *testing.T) {
+	cfg := DefaultConfig()
+	if !cfg.Tools.Web.PreferNative {
+		t.Fatal("DefaultConfig().Tools.Web.PreferNative should be true")
+	}
+}
+
+func TestLoadConfig_WebPreferNativeDefaultsTrueWhenUnset(t *testing.T) {
+	dir := t.TempDir()
+	configPath := filepath.Join(dir, "config.json")
+	if err := os.WriteFile(configPath, []byte(`{"tools":{"web":{"enabled":true}}}`), 0o600); err != nil {
+		t.Fatalf("WriteFile() error: %v", err)
+	}
+
+	cfg, err := LoadConfig(configPath)
+	if err != nil {
+		t.Fatalf("LoadConfig() error: %v", err)
+	}
+	if !cfg.Tools.Web.PreferNative {
+		t.Fatal("PreferNative should remain true when unset in config file")
+	}
+}
+
+func TestLoadConfig_WebPreferNativeCanBeDisabled(t *testing.T) {
+	dir := t.TempDir()
+	configPath := filepath.Join(dir, "config.json")
+	if err := os.WriteFile(configPath, []byte(`{"tools":{"web":{"prefer_native":false}}}`), 0o600); err != nil {
+		t.Fatalf("WriteFile() error: %v", err)
+	}
+
+	cfg, err := LoadConfig(configPath)
+	if err != nil {
+		t.Fatalf("LoadConfig() error: %v", err)
+	}
+	if cfg.Tools.Web.PreferNative {
+		t.Fatal("PreferNative should be false when disabled in config file")
+	}
+}
+
 func TestDefaultConfig_ExecAllowRemoteEnabled(t *testing.T) {
 	cfg := DefaultConfig()
 	if !cfg.Tools.Exec.AllowRemote {

pkg/config/defaults.go

@@ -411,6 +411,7 @@ func DefaultConfig() *Config {
 				ToolConfig: ToolConfig{
 					Enabled: true,
 				},
+				PreferNative:    true,
 				Proxy:           "",
 				FetchLimitBytes: 10 * 1024 * 1024, // 10MB by default
 				Format:          "plaintext",