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.
LOCK(cs_wallet);
    auto it = mapWallet.find(ptx->GetHash());
    if (it != mapWallet.end()) {
        it->second.fInMempool = false;
    }
}
void CWallet::BlockConnected(const CBlock& block, const std::vector<CTransactionRef>& vtxConflicted) {
    const uint256& block_hash = block.GetHash();
    auto locked_chain = chain().lock();
    LOCK(cs_wallet);
    
    
    
    
    
    
    
    for (const CTransactionRef& ptx : vtxConflicted) {
        SyncTransaction(ptx, {} , 0 );
        TransactionRemovedFromMempool(ptx);
    }
    for (size_t i = 0; i < block.vtx.size(); i++) {
        SyncTransaction(block.vtx[i], block_hash, i);
        TransactionRemovedFromMempool(block.vtx[i]);
    }
    m_last_block_processed = block_hash;
}
void CWallet::BlockDisconnected(const CBlock& block) {