Several issues

[razaqq]

There is a whole range of bugs and missing things, ill try to summarize them here in one

• BININT2 (opcode 77) is missing, should be uint16_t
• you should be using wstring often times, because torrent names/files can contain unicode characters
• here you should be adding

        if (i >= box.Files.size())
            break;

for me it was the case that filePriorities.size() > box.Files.size() for multiple torrents, causing an array out of range access and thus crash

• Files renamed in deluge dont transfer their name into transmission
• File priorities (including skip) dont transfer from deluge into transmission
• Various string_view and constexpr missing, not that important
• this is not going to work on windows, because it includes the character : from the timestamp in the filename, which is not allowed. You could replace it with some other character like this

static std::string ReplaceAll(std::string_view str, std::string_view before, std::string_view after)
{
    std::string newString;
    newString.reserve(str.length());

    size_t i = 0, j = 0;

    while ((i = str.find(before, j)) != std::string_view::npos)
    {
        newString.append(str, j, i - j);
        newString.append(after);
        j = i + before.length();
    }

    newString.append(str.substr(j));

    return newString;
}

fs::path MigrationTransaction::GetTemporaryPath(fs::path const& path) const
{
    fs::path result = path;
    result += ".tmp." + ReplaceAll(m_transactionId, ":", "-");
    return result;
}

fs::path MigrationTransaction::GetBackupPath(fs::path const& path) const
{
    fs::path result = path;
    result += ".bak." + ReplaceAll(m_transactionId, ":", "-");
    return result;
}

[mikedld]

I appreciate your interest in the project, but as before please prefer multiple targeted PRs instead of a single big one with all the changes ;)