AFAICT, as of commit a0a422c,  we have 2 different logics to evict outbound peers : lagging-chain (`ConsiderEviction`) and (`CheckForStaleTipAndEvictPeers`). The former to sanitize out lazy/buggy peers who have never sent us a valid header and are always staying behind our tip, the latter triggered in case of stale tip due to block variance to seek a better chain by rotating our outbound peers if we already reach an outbound limit (`EvictExtraOutboundPeers`).

Block-relay-only peers were introduced by #15719. Contrary to outbound full-relay peers who provided us at least a useful header, they're not protected by lagging-chain eviction.

We actually have a comment inside `ProcessHeadersMessage` indicating the contrary behavior. We should either document cleanly that block-relay-only aren't protected or effectively extend the scope of protection to them.

Hinted during #19724 review, see https://github.com/bitcoin/bitcoin/pull/19724#discussion_r475144532
* peers announce compact blocks.
 */
void PeerManager::BlockChecked(const CBlock& block, const BlockValidationState& state) {
    LOCK(cs_main);
    const uint256 hash(block.GetHash());
    std::map<uint256, std::pair<NodeId, bool>>::iterator it = mapBlockSource.find(hash);
    
    
    if (state.IsInvalid() &&
        it != mapBlockSource.end() &&
        State(it->second.first)) {
            MaybePunishNodeForBlock( it->second.first, state,  !it->second.second);
    }
    
    
    
    
    
    
    else if (state.IsValid() &&
             !::ChainstateActive().IsInitialBlockDownload() &&
             mapBlocksInFlight.count(hash) == mapBlocksInFlight.size()) {
        if (it != mapBlockSource.end()) {
            MaybeSetPeerAsAnnouncingHeaderAndIDs(it->second.first, m_connman);
        }
    }
    if (it != mapBlockSource.end())
        mapBlockSource.erase(it);
}
bool static AlreadyHaveTx(const GenTxid& gtxid, const CTxMemPool& mempool) EXCLUSIVE_LOCKS_REQUIRED(cs_main)