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.
fUpdateConnectionTime = false;
    LOCK(cs_main);
    CNodeState *state = State(nodeid);
    assert(state != nullptr);
    if (state->fSyncStarted)
        nSyncStarted--;
    if (state->nMisbehavior == 0 && state->fCurrentlyConnected) {
        fUpdateConnectionTime = true;
    }
    for (const QueuedBlock& entry : state->vBlocksInFlight) {
        mapBlocksInFlight.erase(entry.hash);
    }
    EraseOrphansFor(nodeid);
    nPreferredDownload -= state->fPreferredDownload;
    nPeersWithValidatedDownloads -= (state->nBlocksInFlightValidHeaders != 0);
    assert(nPeersWithValidatedDownloads >= 0);
    g_outbound_peers_with_protect_from_disconnect -= state->m_chain_sync.m_protect;
    assert(g_outbound_peers_with_protect_from_disconnect >= 0);
    mapNodeState.erase(nodeid);
    if (mapNodeState.empty()) {
        
        assert(mapBlocksInFlight.empty());
        assert(nPreferredDownload == 0);
        assert(nPeersWithValidatedDownloads == 0);
        assert(g_outbound_peers_with_protect_from_disconnect == 0);
    }
    LogPrint(BCLog::NET, "Cleared nodestate for peer=%d\n", nodeid);
}
bool GetNodeStateStats(NodeId nodeid, CNodeStateStats &stats) {