providers: implement native web search for OpenAI and Codex

pkg/providers/codex_provider.go

@@ -157,6 +157,10 @@ func (p *CodexProvider) GetDefaultModel() string {
 	return codexDefaultModel
 }
 
+func (p *CodexProvider) SupportsNativeSearch() bool {
+	return p.enableWebSearch
+}
+
 func resolveCodexModel(model string) (string, string) {
 	m := strings.ToLower(strings.TrimSpace(model))
 	if m == "" {

pkg/providers/http_provider.go

@@ -55,3 +55,7 @@ func (p *HTTPProvider) Chat(
 func (p *HTTPProvider) GetDefaultModel() string {
 	return ""
 }
+
+func (p *HTTPProvider) SupportsNativeSearch() bool {
+	return p.delegate.SupportsNativeSearch()
+}

pkg/providers/openai_compat/provider.go

@@ -103,8 +103,11 @@ func (p *Provider) Chat(
 		"messages": common.SerializeMessages(messages),
 	}
 
-	if len(tools) > 0 {
-		requestBody["tools"] = tools
+	// When fallback uses a different provider (e.g. DeepSeek), that provider must not inject web_search_preview.
+	nativeSearch, _ := options["native_search"].(bool)
+	nativeSearch = nativeSearch && isNativeSearchHost(p.apiBase)
+	if len(tools) > 0 || nativeSearch {
+		requestBody["tools"] = buildToolsList(tools, nativeSearch)
 		requestBody["tool_choice"] = "auto"
 	}
 
@@ -195,6 +198,33 @@ func normalizeModel(model, apiBase string) string {
 	}
 }
 
+func buildToolsList(tools []ToolDefinition, nativeSearch bool) []any {
+	result := make([]any, 0, len(tools)+1)
+	for _, t := range tools {
+		if nativeSearch && strings.EqualFold(t.Function.Name, "web_search") {
+			continue
+		}
+		result = append(result, t)
+	}
+	if nativeSearch {
+		result = append(result, map[string]any{"type": "web_search_preview"})
+	}
+	return result
+}
+
+func (p *Provider) SupportsNativeSearch() bool {
+	return isNativeSearchHost(p.apiBase)
+}
+
+func isNativeSearchHost(apiBase string) bool {
+	u, err := url.Parse(apiBase)
+	if err != nil {
+		return false
+	}
+	host := u.Hostname()
+	return host == "api.openai.com" || strings.HasSuffix(host, ".openai.azure.com")
+}
+
 // supportsPromptCacheKey reports whether the given API base is known to
 // support the prompt_cache_key request field. Currently only OpenAI's own
 // API and Azure OpenAI support this. All other OpenAI-compatible providers