The `Broadcast`/`ResendWalletTransactions` interface is strange:

- it's the node saying to the wallet "Try to submit your unconfirmed transactions to the mempool again"
- it's called in one place by the node, in `SendMessages()` here: https://github.com/bitcoin/bitcoin/blob/c033c4b5cef89a654e4d9d5c5f9bd823871b068b/src/net_processing.cpp#L3515. `SendMessages()` is called on the message handling thread on a loop.
- the actual scheduling of when the wallet sends messages is handled in the `ResendWalletTransactions()` function itself, using the `nNextResend` and `nLastResend` wallet globals (which could as easily be static variables in `ResendWalletTransactions()`).

Therefore the only use of `Broadcast()` is to periodically prod the wallet. The wallet itself decides whether it's time to resend transactions. This could be done by scheduling regular calls to `ResendWalletTransactions()`, in the same way that we schedule regular wallet flushes here: https://github.com/bitcoin/bitcoin/blob/c033c4b5cef89a654e4d9d5c5f9bd823871b068b/src/wallet/init.cpp#L215.

A couple of minor implementation details:

- the call to `Broadcast()` in `SendMessages()` is protected by an if statement `if (!fReindex && !fImporting && !IsInitialBlockDownload()) {`. Those tests could be moved into `ResendWalletTransactions()` (through the `Chain` interface).
- The `Broadcast` notification passes in the `nTimeBestReceived` time of the best block. That could be fetched by `ResendWalletTransactions()` through the `Chain` interface.
"or (for backwards compatibility) the name of an existing data file in -walletdir (%s)",
              location.GetName(), GetWalletDir());
        return false;
    }
    
    if (IsWalletLoaded(wallet_path)) {
        error_string = strprintf("Error loading wallet %s. Duplicate -wallet filename specified.", location.GetName());
        return false;
    }
    
    std::unique_ptr<WalletDatabase> database = WalletDatabase::Create(wallet_path);
    try {
        if (!WalletBatch::VerifyEnvironment(wallet_path, error_string)) {
            return false;
        }
    } catch (const fs::filesystem_error& e) {
        error_string = strprintf("Error loading wallet %s. %s", location.GetName(), fsbridge::get_filesystem_error_message(e));
        return false;
    }
    if (salvage_wallet) {
        
        CWallet dummyWallet(chain, WalletLocation(), WalletDatabase::CreateDummy());
        std::string backup_filename;
        if (!WalletBatch::Recover(wallet_path, (void *)&dummyWallet, WalletBatch::RecoverKeysOnlyFilter, backup_filename)) {
            return false;
        }
    }
    return WalletBatch::VerifyDatabaseFile(wallet_path, warning_string, error_string);
}
std::shared_ptr<CWallet> CWallet::CreateWalletFromFile(interfaces::Chain& chain, const WalletLocation& location, uint64_t wallet_creation_flags)