fix(tools): improve web search provider fallback (#2629)

- centralize web search provider readiness and resolution logic
- fall back when the configured provider is unavailable or invalid
- allow native-search-capable models to use built-in search without the client tool
- simplify the tools page and add direct access to web search settings
- add backend, agent, and integration tests for the new selection behavior

web/backend/api/tools_test.go

@@ -198,6 +198,66 @@ func TestHandleUpdateToolState(t *testing.T) {
 	}
 }
 
+func TestHandleListTools_ReportsWebSearchEnabledWhenToolIsOn(t *testing.T) {
+	tests := []struct {
+		name         string
+		preferNative bool
+	}{
+		{name: "without prefer_native", preferNative: false},
+		{name: "with prefer_native", preferNative: true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			configPath, cleanup := setupOAuthTestEnv(t)
+			defer cleanup()
+
+			cfg, err := config.LoadConfig(configPath)
+			if err != nil {
+				t.Fatalf("LoadConfig() error = %v", err)
+			}
+			cfg.Tools.Web.PreferNative = tt.preferNative
+			cfg.Tools.Web.Provider = "brave"
+			cfg.Tools.Web.Sogou.Enabled = false
+			cfg.Tools.Web.DuckDuckGo.Enabled = false
+			cfg.Tools.Web.Brave.Enabled = true
+			cfg.Tools.Web.Brave.SetAPIKeys(nil)
+			if err := config.SaveConfig(configPath, cfg); err != nil {
+				t.Fatalf("SaveConfig() error = %v", err)
+			}
+
+			h := NewHandler(configPath)
+			mux := http.NewServeMux()
+			h.RegisterRoutes(mux)
+
+			rec := httptest.NewRecorder()
+			req := httptest.NewRequest(http.MethodGet, "/api/tools", nil)
+			mux.ServeHTTP(rec, req)
+
+			if rec.Code != http.StatusOK {
+				t.Fatalf("status = %d, want %d, body=%s", rec.Code, http.StatusOK, rec.Body.String())
+			}
+
+			var resp toolSupportResponse
+			if err := json.Unmarshal(rec.Body.Bytes(), &resp); err != nil {
+				t.Fatalf("Unmarshal() error = %v", err)
+			}
+
+			for _, tool := range resp.Tools {
+				if tool.Name != "web_search" {
+					continue
+				}
+				if tool.Status != "enabled" || tool.ReasonCode != "" {
+					t.Fatalf("web_search = %#v, want enabled with no reason code", tool)
+				}
+				return
+			}
+
+			t.Fatal("expected web_search in response")
+		})
+	}
+}
+
 func TestHandleGetWebSearchConfig(t *testing.T) {
 	configPath, cleanup := setupOAuthTestEnv(t)
 	defer cleanup()
@@ -206,6 +266,7 @@ func TestHandleGetWebSearchConfig(t *testing.T) {
 	if err != nil {
 		t.Fatalf("LoadConfig() error = %v", err)
 	}
+	cfg.Tools.Web.PreferNative = false
 	cfg.Tools.Web.Provider = "sogou"
 	cfg.Tools.Web.Sogou.Enabled = true
 	cfg.Tools.Web.Sogou.MaxResults = 6
@@ -242,6 +303,48 @@ func TestHandleGetWebSearchConfig(t *testing.T) {
 	}
 }
 
+func TestHandleGetWebSearchConfig_DoesNotExposeNativeAsCurrentService(t *testing.T) {
+	configPath, cleanup := setupOAuthTestEnv(t)
+	defer cleanup()
+
+	cfg, err := config.LoadConfig(configPath)
+	if err != nil {
+		t.Fatalf("LoadConfig() error = %v", err)
+	}
+	cfg.Tools.Web.PreferNative = true
+	cfg.Tools.Web.Provider = "brave"
+	cfg.Tools.Web.Sogou.Enabled = false
+	cfg.Tools.Web.DuckDuckGo.Enabled = false
+	cfg.Tools.Web.Brave.Enabled = true
+	cfg.Tools.Web.Brave.SetAPIKeys(nil)
+	if err := config.SaveConfig(configPath, cfg); err != nil {
+		t.Fatalf("SaveConfig() error = %v", err)
+	}
+
+	h := NewHandler(configPath)
+	mux := http.NewServeMux()
+	h.RegisterRoutes(mux)
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequest(http.MethodGet, "/api/tools/web-search-config", nil)
+	mux.ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("status = %d, want %d, body=%s", rec.Code, http.StatusOK, rec.Body.String())
+	}
+
+	var resp webSearchConfigResponse
+	if err := json.Unmarshal(rec.Body.Bytes(), &resp); err != nil {
+		t.Fatalf("Unmarshal() error = %v", err)
+	}
+	if !resp.PreferNative {
+		t.Fatal("prefer_native should remain true in response")
+	}
+	if resp.CurrentService != "" {
+		t.Fatalf("current_service = %q, want empty when no external provider is ready", resp.CurrentService)
+	}
+}
+
 func TestHandleUpdateWebSearchConfig(t *testing.T) {
 	configPath, cleanup := setupOAuthTestEnv(t)
 	defer cleanup()
@@ -393,6 +496,27 @@ func TestResolveCurrentWebSearchProvider_PrefersConfiguredProvidersBeforeSogou(t
 	}
 }
 
+func TestResolveCurrentWebSearchProvider_FallsBackWhenExplicitProviderUnavailable(t *testing.T) {
+	cfg := config.DefaultConfig()
+	cfg.Tools.Web.Provider = "brave"
+	cfg.Tools.Web.Brave.Enabled = true
+	cfg.Tools.Web.Sogou.Enabled = true
+
+	if got := resolveCurrentWebSearchProvider(cfg); got != "sogou" {
+		t.Fatalf("resolveCurrentWebSearchProvider() = %q, want sogou", got)
+	}
+}
+
+func TestResolveCurrentWebSearchProvider_FallsBackWhenProviderIsUnknown(t *testing.T) {
+	cfg := config.DefaultConfig()
+	cfg.Tools.Web.Provider = "totally_unknown"
+	cfg.Tools.Web.Sogou.Enabled = true
+
+	if got := resolveCurrentWebSearchProvider(cfg); got != "sogou" {
+		t.Fatalf("resolveCurrentWebSearchProvider() = %q, want sogou", got)
+	}
+}
+
 func TestResolveCurrentWebSearchProvider_UsesPreferredLanguageForSogouAndDuckDuckGo(t *testing.T) {
 	cfg := config.DefaultConfig()
 	cfg.Tools.Web.Provider = "auto"
@@ -413,3 +537,22 @@ func TestResolveCurrentWebSearchProvider_UsesPreferredLanguageForSogouAndDuckDuc
 		t.Fatalf("resolveCurrentWebSearchProvider() = %q, want sogou", got)
 	}
 }
+
+func TestResolveCurrentWebSearchProvider_IgnoresPreferNativeInConfigView(t *testing.T) {
+	cfg := config.DefaultConfig()
+	cfg.ModelList = []*config.ModelConfig{{
+		ModelName: "custom-default",
+		Model:     "openai/gpt-4o",
+		APIKeys:   config.SimpleSecureStrings("sk-default"),
+	}}
+	cfg.Agents.Defaults.ModelName = "custom-default"
+	cfg.Tools.Web.PreferNative = true
+	cfg.Tools.Web.Provider = "brave"
+	cfg.Tools.Web.Sogou.Enabled = false
+	cfg.Tools.Web.DuckDuckGo.Enabled = false
+	cfg.Tools.Web.Brave.Enabled = true
+
+	if got := resolveCurrentWebSearchProvider(cfg); got != "" {
+		t.Fatalf("resolveCurrentWebSearchProvider() = %q, want empty when only native search would be available", got)
+	}
+}