add comment addressing reasoning for hex encoding

x/ibc/core/02-client/keeper/client.go

@@ -100,6 +100,9 @@ func (k Keeper) UpdateClient(ctx sdk.Context, clientID string, header exported.H
 	// emit the full header in events
 	var headerStr string
 	if header != nil {
+		// Marshal the Header as an Any and encode the resulting bytes to hex.
+		// This prevents the event value from containing invalid UTF-8 characters
+		// which may cause data to be lost when JSON encoding/decoding.
 		headerStr = hex.EncodeToString(types.MustMarshalHeader(k.cdc, header))
 
 	}