"System.arraycopy should throw for insufficient destination space");
    }

    @Test
    @DisplayName("encode() throws when dstIndex causes overflow")
    void encodeThrowsWhenDstIndexCausesOverflow() {
        byte[] src = makeSeq(5);
        Encodable enc = new ByteEncodable(src, 0, 5);
        byte[] dst = new byte[6]; // size is 6, but index 2 + len 5 -> overflow