fix(gateway): stop default redact thinking beta injection

backend/internal/pkg/claude/constants.go

@@ -75,6 +75,7 @@ const CLICurrentVersion = "2.1.92"
 //   - OAuth 账号 + 非 haiku：追加这整份列表，再按需保留 client 带来的 beta。
 //   - OAuth 账号 + haiku：Anthropic 对 haiku 不做 third-party 判定，使用 HaikuBetaHeader 即可。
 //   - API-key 账号：不要使用本函数，参见 APIKeyBetaHeader。
+//   - 不默认加入 redact-thinking，避免上游抹除 thinking 内容；客户端显式传入时由合并逻辑保留。
 func FullClaudeCodeMimicryBetas() []string {
 	return []string{
 		BetaClaudeCode,
@@ -82,7 +83,6 @@ func FullClaudeCodeMimicryBetas() []string {
 		BetaInterleavedThinking,
 		BetaPromptCachingScope,
 		BetaEffort,
-		BetaRedactThinking,
 		BetaContextManagement,
 		BetaExtendedCacheTTL,
 	}

backend/internal/service/gateway_beta_test.go

@@ -124,6 +124,24 @@ func TestMergeAnthropicBetaDropping_DroppedBetas(t *testing.T) {
 	require.Contains(t, got, "fast-mode-2026-02-01")
 }
 
+func TestFullClaudeCodeMimicryBetas_DoesNotDefaultRedactThinking(t *testing.T) {
+	required := claude.FullClaudeCodeMimicryBetas()
+
+	require.NotContains(t, required, claude.BetaRedactThinking)
+	require.Contains(t, required, claude.BetaClaudeCode)
+	require.Contains(t, required, claude.BetaOAuth)
+	require.Contains(t, required, claude.BetaInterleavedThinking)
+}
+
+func TestMergeAnthropicBetaDropping_PreservesIncomingRedactThinking(t *testing.T) {
+	required := claude.FullClaudeCodeMimicryBetas()
+	incoming := claude.BetaRedactThinking
+
+	got := mergeAnthropicBetaDropping(required, incoming, droppedBetaSet())
+
+	require.Contains(t, got, claude.BetaRedactThinking)
+}
+
 func TestDroppedBetaSet(t *testing.T) {
 	// Base set contains DroppedBetas (now empty — filtering moved to configurable beta policy)
 	base := droppedBetaSet()