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
};
using PeerRef = std::shared_ptr<Peer>;
/**
 * Map of all Peer objects, keyed by peer id. This map is protected
 * by the global g_peer_mutex. Once a shared pointer reference is
 * taken, the lock may be released. Individual fields are protected by
 * their own locks.
 */
Mutex g_peer_mutex;
static std::map<NodeId, PeerRef> g_peer_map GUARDED_BY(g_peer_mutex);
/** Get a shared pointer to the Peer object.
 *  May return nullptr if the Peer object can't be found. */
static PeerRef GetPeerRef(NodeId id)
{
    LOCK(g_peer_mutex);
    auto it = g_peer_map.find(id);
    return it != g_peer_map.end() ? it->second : nullptr;
}
static void UpdatePreferredDownload(const CNode& node, CNodeState* state) EXCLUSIVE_LOCKS_REQUIRED(cs_main)