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backend/internal/util/claude_attribution.go

@@ -0,0 +1,69 @@
+package util
+
+import (
+	"strings"
+	"unicode"
+
+	"github.com/tidwall/gjson"
+	"github.com/tidwall/sjson"
+)
+
+const claudeCodeAttributionSystemPrefix = "x-anthropic-billing-header:"
+
+// IsClaudeCodeAttributionSystemText reports whether text is the Claude Code
+// attribution block that carries per-request billing and prompt fingerprint data.
+func IsClaudeCodeAttributionSystemText(text string) bool {
+	text = strings.TrimLeftFunc(text, unicode.IsSpace)
+	return strings.HasPrefix(text, claudeCodeAttributionSystemPrefix)
+}
+
+// StripClaudeCodeAttributionSystem removes Claude Code billing/CCH attribution
+// blocks from a Messages body. Other system content is kept. Providers such as
+// Kimi and Antigravity may treat this block as prompt text, so callers use this
+// helper when the active policy has not explicitly opted into a full CLI profile.
+func StripClaudeCodeAttributionSystem(payload []byte) []byte {
+	system := gjson.GetBytes(payload, "system")
+	if !system.Exists() {
+		return payload
+	}
+	if system.Type == gjson.String {
+		if !IsClaudeCodeAttributionSystemText(system.String()) {
+			return payload
+		}
+		updated, errDelete := sjson.DeleteBytes(payload, "system")
+		if errDelete != nil {
+			return payload
+		}
+		return updated
+	}
+	if !system.IsArray() {
+		return payload
+	}
+	kept := make([]string, 0, len(system.Array()))
+	removed := false
+	system.ForEach(func(_, block gjson.Result) bool {
+		if block.Get("type").String() == "text" && IsClaudeCodeAttributionSystemText(block.Get("text").String()) {
+			removed = true
+			return true
+		}
+		if block.Raw != "" {
+			kept = append(kept, block.Raw)
+		}
+		return true
+	})
+	if !removed {
+		return payload
+	}
+	if len(kept) == 0 {
+		updated, errDelete := sjson.DeleteBytes(payload, "system")
+		if errDelete != nil {
+			return payload
+		}
+		return updated
+	}
+	updated, errSet := sjson.SetRawBytes(payload, "system", []byte("["+strings.Join(kept, ",")+"]"))
+	if errSet != nil {
+		return payload
+	}
+	return updated
+}