Keep launcher locale changes from mutating shared web-search routing (#2573)

The launcher wired UI language changes into a process-global backend
switch that changed auto web-search provider selection and the
reported current service for every handler in the same process.

This narrows the fix to the validated leak: remove backend sync from
frontend locale changes, drop the now-unused UI endpoint, and make
auto selection fall back to a stable default when the query itself
does not contain a script hint.

Constraint: Keep the patch small and mergeable without redesigning per-user preference storage
Rejected: Add per-user backend language state | larger scope than the validated bug and unclear maintainer preference
Rejected: Persist preferred language in config | still shares mutable state across clients of the same instance
Confidence: high
Scope-risk: narrow
Reversibility: clean
Directive: If locale-aware provider routing is reintroduced later, scope it to explicit config or request context instead of package-global state
Tested: go test ./web/backend/api ./pkg/tools -count=1; pnpm lint; pnpm build
Not-tested: Full make check; live multi-browser manual launcher run after the backend endpoint removal

pkg/tools/integration/web.go

@@ -58,8 +58,6 @@ var (
 	reSogouRealURL = regexp.MustCompile(`url=([^&]+)`)
 )
 
-var preferredWebSearchLanguage atomic.Value
-
 type APIKeyPool struct {
 	keys    []string
 	current uint32
@@ -250,27 +248,6 @@ func mapBaiduRecencyFilter(rangeCode string) string {
 	}
 }
 
-func normalizePreferredWebSearchLanguage(lang string) string {
-	lang = strings.ToLower(strings.TrimSpace(lang))
-	switch {
-	case strings.HasPrefix(lang, "zh"), lang == "chinese":
-		return "zh"
-	case strings.HasPrefix(lang, "en"), lang == "english":
-		return "en"
-	default:
-		return ""
-	}
-}
-
-func SetPreferredWebSearchLanguage(lang string) {
-	preferredWebSearchLanguage.Store(normalizePreferredWebSearchLanguage(lang))
-}
-
-func GetPreferredWebSearchLanguage() string {
-	lang, _ := preferredWebSearchLanguage.Load().(string)
-	return lang
-}
-
 type BraveSearchProvider struct {
 	keyPool *APIKeyPool
 	proxy   string
@@ -1420,7 +1397,7 @@ func containsLatinLetter(text string) bool {
 func prefersDuckDuckGoQuery(text string) bool {
 	trimmed := strings.TrimSpace(text)
 	if trimmed == "" {
-		return GetPreferredWebSearchLanguage() == "en"
+		return false
 	}
 	if containsHan(trimmed) {
 		return false
@@ -1428,7 +1405,7 @@ func prefersDuckDuckGoQuery(text string) bool {
 	if containsLatinLetter(trimmed) {
 		return true
 	}
-	return GetPreferredWebSearchLanguage() == "en"
+	return false
 }
 
 func (opts WebSearchToolOptions) buildProviderResolver() (func(query string) (SearchProvider, int), error) {

pkg/tools/integration/web_test.go

@@ -1778,11 +1778,6 @@ func TestApplySogouRangeHint(t *testing.T) {
 }
 
 func TestPrefersDuckDuckGoQuery(t *testing.T) {
-	SetPreferredWebSearchLanguage("")
-	t.Cleanup(func() {
-		SetPreferredWebSearchLanguage("")
-	})
-
 	tests := []struct {
 		name  string
 		query string
@@ -1805,19 +1800,9 @@ func TestPrefersDuckDuckGoQuery(t *testing.T) {
 	}
 }
 
-func TestPrefersDuckDuckGoQuery_FallsBackToPreferredLanguage(t *testing.T) {
-	SetPreferredWebSearchLanguage("en")
-	t.Cleanup(func() {
-		SetPreferredWebSearchLanguage("")
-	})
-
-	if !prefersDuckDuckGoQuery("2026 04 15") {
-		t.Fatal("numeric query should prefer DuckDuckGo when preferred language is English")
-	}
-
-	SetPreferredWebSearchLanguage("zh")
+func TestPrefersDuckDuckGoQuery_DoesNotUseGlobalLanguageFallback(t *testing.T) {
 	if prefersDuckDuckGoQuery("2026 04 15") {
-		t.Fatal("numeric query should prefer Sogou when preferred language is Chinese")
+		t.Fatal("numeric query should default to Sogou when no script-specific hint is present")
 	}
 }
 

pkg/tools/integration_facade.go

@@ -65,14 +65,6 @@ func NewAPIKeyPool(keys []string) *APIKeyPool {
 	return integrationtools.NewAPIKeyPool(keys)
 }
 
-func SetPreferredWebSearchLanguage(lang string) {
-	integrationtools.SetPreferredWebSearchLanguage(lang)
-}
-
-func GetPreferredWebSearchLanguage() string {
-	return integrationtools.GetPreferredWebSearchLanguage()
-}
-
 func WebSearchToolOptionsFromConfig(cfg *config.Config) WebSearchToolOptions {
 	return integrationtools.WebSearchToolOptionsFromConfig(cfg)
 }