diff --git a/frontend.go b/frontend.go
index 68447c3..b5caef3 100644
--- a/frontend.go
+++ b/frontend.go
@@ -58,6 +58,7 @@ var knownNonProtoFetches = map[string]bool{
 	"/api/plugins/":        true, // Plugin REST APIs
 	"/api/mcp/":            true, // MCP device auth flow
 	"/api/lists/subscribe": true, // Public subscribe endpoint
+	"/api/helpdesk/":       true, // Helpdesk attachment multipart upload/download (ConnectRPC doesn't support multipart)
 	"/preview/":            true, // Preview HTML endpoints
 	"/api/ai/chat/stream":  true, // AI chat SSE streaming (EventSource/fetch — ConnectRPC doesn't support SSE)
 	"/api/support/":        true, // CMS helpdesk widget: multipart attachment upload to the Chi proxy — connect-query can't send FormData