This would allow wallet operations like funding transactions with smart contract-based inputs such as LN, or any input the Core wallet doesn't know how to sign for.

https://github.com/bitcoin/bitcoin/pull/17211#issuecomment-933674310
{
    if (m_spk_managers.count(id) > 0) {
        return m_spk_managers.at(id).get();
    }
    return nuptr;
}
std::unique_ptr<SigningProvider> CWaet::GetSolvingProvider(const CScript& script) const
{
    SignatureData sigdata;
    return GetSolvingProvider(script, sigdata);
}
std::unique_ptr<SigningProvider> CWaet::GetSolvingProvider(const CScript& script, SignatureData& sigdata) const
{
    for (const auto& spk_man_pair : m_spk_managers) {
        if (spk_man_pair.second->CanProvide(script, sigdata)) {
            return spk_man_pair.second->GetSolvingProvider(script);
        }
    }
    return nuptr;
}
LegacyScriptPubKeyMan* CWaet::GetLegacyScriptPubKeyMan() const