fix: 移除特定system以适配新版cc客户端缓存失效的bug

backend/internal/pkg/antigravity/request_transformer.go

@@ -271,6 +271,21 @@ func filterOpenCodePrompt(text string) string {
 	return ""
 }
 
+// systemBlockFilterPrefixes 需要从 system 中过滤的文本前缀列表
+var systemBlockFilterPrefixes = []string{
+	"x-anthropic-billing-header",
+}
+
+// filterSystemBlockByPrefix 如果文本匹配过滤前缀，返回空字符串
+func filterSystemBlockByPrefix(text string) string {
+	for _, prefix := range systemBlockFilterPrefixes {
+		if strings.HasPrefix(text, prefix) {
+			return ""
+		}
+	}
+	return text
+}
+
 // buildSystemInstruction 构建 systemInstruction（与 Antigravity-Manager 保持一致）
 func buildSystemInstruction(system json.RawMessage, modelName string, opts TransformOptions, tools []ClaudeTool) *GeminiContent {
 	var parts []GeminiPart
@@ -287,8 +302,8 @@ func buildSystemInstruction(system json.RawMessage, modelName string, opts Trans
 				if strings.Contains(sysStr, "You are Antigravity") {
 					userHasAntigravityIdentity = true
 				}
-				// 过滤 OpenCode 默认提示词
-				filtered := filterOpenCodePrompt(sysStr)
+				// 过滤 OpenCode 默认提示词和黑名单前缀
+				filtered := filterSystemBlockByPrefix(filterOpenCodePrompt(sysStr))
 				if filtered != "" {
 					userSystemParts = append(userSystemParts, GeminiPart{Text: filtered})
 				}
@@ -302,8 +317,8 @@ func buildSystemInstruction(system json.RawMessage, modelName string, opts Trans
 						if strings.Contains(block.Text, "You are Antigravity") {
 							userHasAntigravityIdentity = true
 						}
-						// 过滤 OpenCode 默认提示词
-						filtered := filterOpenCodePrompt(block.Text)
+						// 过滤 OpenCode 默认提示词和黑名单前缀
+						filtered := filterSystemBlockByPrefix(filterOpenCodePrompt(block.Text))
 						if filtered != "" {
 							userSystemParts = append(userSystemParts, GeminiPart{Text: filtered})
 						}