fix(protocol): harden gateway contract validation

tools/native_conformance.rs

@@ -56,12 +56,18 @@ fn evaluate(kind: &str, input: &str) -> &'static str {
         "gateway_input" => classify_gateway_input(values.get("hex").map(String::as_str).unwrap_or_default()),
         "gateway_feedback" => classify_gateway_feedback(values.get("hex").map(String::as_str).unwrap_or_default()),
         "gateway_clipboard" if values.contains_key("file") => "invalid:forbidden",
-        "gateway_clipboard"
-            if matches!(values.get("direction").map(String::as_str), Some("client_to_provider") | Some("provider_to_client"))
-                && values.get("encoding").map(String::as_str) == Some("utf-8")
-                && values.get("loop_token").map_or(false, |value| (16..=128).contains(&value.len()))
-                && values.get("text").map_or(false, |value| value.len() <= 65536) => "valid",
-        "gateway_clipboard" => "invalid:clipboard",
+        "gateway_clipboard" => match (
+            values.get("direction"),
+            values.get("text"),
+            values.get("encoding"),
+            values.get("loop_token"),
+        ) {
+            (Some(direction), Some(text), Some(encoding), Some(token))
+                if GatewayClipboardText::new(
+                    direction.clone(), text.clone(), encoding.clone(), token.clone(),
+                ).is_ok() => "valid",
+            _ => "invalid:clipboard",
+        },
         "gateway_clipboard_audit" if values.contains_key("text") => "invalid:forbidden",
         "gateway_clipboard_audit"
             if matches!(values.get("direction").map(String::as_str), Some("client_to_provider") | Some("provider_to_client"))