fips_core/node/

lifecycle.rs

//! Node lifecycle management: start, stop, and peer connection initiation.

use super::{Node, NodeError, NodeState};
use crate::config::{ConnectPolicy, NostrDiscoveryPolicy, PeerAddress, PeerConfig};
use crate::discovery::nostr::{
    ADVERT_IDENTIFIER, ADVERT_VERSION, BootstrapEvent, MeshTraversalSignal, NostrDiscovery,
    OverlayAdvert, OverlayEndpointAdvert, OverlayTransportKind,
};
use crate::discovery::{BootstrapHandoffResult, EstablishedTraversal};
use crate::node::acl::PeerAclContext;
use crate::node::wire::build_msg1;
use crate::peer::PeerConnection;
use crate::protocol::{Disconnect, DisconnectReason, SessionMessageType};
use crate::transport::{Link, LinkDirection, LinkId, TransportAddr, TransportId, packet_channel};
use crate::upper::tun::{TunDevice, TunState, run_tun_reader, shutdown_tun_interface};
use crate::{NodeAddr, PeerIdentity};
use secp256k1::PublicKey;
use std::collections::{HashMap, HashSet};
use std::net::{IpAddr, SocketAddr};
use std::thread;
use std::time::Duration;
use tracing::{debug, info, warn};

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum MeshSignalSessionAction {
    Send,
    Defer,
    Drop,
}

#[cfg(debug_assertions)]
fn node_start_debug_log(message: impl AsRef<str>) {
    use std::io::Write as _;

    if let Ok(mut file) = std::fs::OpenOptions::new()
        .create(true)
        .append(true)
        .open(std::env::temp_dir().join("nvpn-fips-endpoint-debug.log"))
    {
        let _ = writeln!(
            file,
            "{:?} {}",
            std::time::SystemTime::now(),
            message.as_ref()
        );
    }
}

#[cfg(not(debug_assertions))]
fn node_start_debug_log(_message: impl AsRef<str>) {}

/// True if `ip` is not a viable canonical advert endpoint for peers off
/// the publisher's own LAN. Covers RFC1918, loopback, link-local, IPv4
/// CGNAT (100.64/10), unspecified, multicast/benchmark, and IPv6
/// unique-local/loopback/unspecified. We never publish these as the
/// peer's primary `runtime_endpoint`; an off-LAN consumer can't route
/// to them, and latching one in onto a slow overlay-relay fallback is
/// the original bug this guard exists to prevent.
fn is_unroutable_advert_ip(ip: IpAddr) -> bool {
    match ip {
        IpAddr::V4(v4) => {
            v4.is_private()
                || v4.is_loopback()
                || v4.is_link_local()
                || v4.is_unspecified()
                || v4.is_multicast()
                || v4.is_broadcast()
                || v4.is_documentation()
                // 100.64.0.0/10 — CGNAT, RFC 6598. Not routable on the
                // public internet; behaves like an extra NAT layer.
                || (v4.octets()[0] == 100 && (v4.octets()[1] & 0xc0) == 64)
        }
        IpAddr::V6(v6) => {
            v6.is_loopback()
                || v6.is_unspecified()
                || v6.is_unique_local()
                || v6.is_multicast()
                // IPv6 link-local: fe80::/10
                || (v6.segments()[0] & 0xffc0) == 0xfe80
        }
    }
}

fn socket_addr_families_compatible(local: SocketAddr, remote: SocketAddr) -> bool {
    matches!(
        (local, remote),
        (SocketAddr::V4(_), SocketAddr::V4(_)) | (SocketAddr::V6(_), SocketAddr::V6(_))
    )
}

const OPEN_DISCOVERY_RETRY_LIFETIME_MULTIPLIER: u64 = 2;
const MAX_PARALLEL_PATH_CANDIDATES_PER_PEER: usize = 4;
const MAX_AUTO_CONNECT_GRAPH_WARMUPS_PER_TICK: usize = 16;
const MAX_DISCOVERY_CONNECTS_PER_TICK: usize = 16;

impl Node {
    /// Initiate connections to configured static peers.
    ///
    /// For each peer configured with AutoConnect policy, creates a link and
    /// peer entry, then starts the Noise handshake by sending the first message.
    /// Replace the runtime peer list. Newly added auto-connect peers get
    /// `initiate_peer_connection` immediately; removed peers are dropped from
    /// the retry queue (the regular liveness timeout reaps any active session
    /// — we don't proactively disconnect, since the same npub might be on its
    /// way back via a fresh advert). Existing auto-connect entries with new
    /// direct addresses are dialed immediately, and retry state is refreshed
    /// so later attempts also use the latest hints.
    pub(super) async fn update_peers(
        &mut self,
        new_peers: Vec<crate::config::PeerConfig>,
    ) -> Result<crate::node::UpdatePeersOutcome, crate::node::NodeError> {
        use std::collections::{HashMap, HashSet};

        let mut new_by_addr: HashMap<crate::identity::NodeAddr, crate::config::PeerConfig> =
            HashMap::with_capacity(new_peers.len());
        let mut new_order = Vec::with_capacity(new_peers.len());
        for peer in new_peers {
            let identity = match PeerIdentity::from_npub(&peer.npub) {
                Ok(id) => id,
                Err(e) => {
                    return Err(crate::node::NodeError::InvalidPeerNpub {
                        npub: peer.npub.clone(),
                        reason: e.to_string(),
                    });
                }
            };
            // Last-write-wins on duplicates so callers passing a multi-source
            // candidate list (e.g. operator hints + recent-peers cache for
            // the same npub) get the merge they meant.
            let node_addr = *identity.node_addr();
            if !new_by_addr.contains_key(&node_addr) {
                new_order.push(node_addr);
            }
            new_by_addr.insert(node_addr, peer);
        }

        let current_by_addr: HashMap<crate::identity::NodeAddr, crate::config::PeerConfig> = self
            .config
            .peers()
            .iter()
            .filter_map(|pc| {
                PeerIdentity::from_npub(&pc.npub)
                    .ok()
                    .map(|id| (*id.node_addr(), pc.clone()))
            })
            .collect();

        let new_addrs: HashSet<_> = new_by_addr.keys().copied().collect();
        let current_addrs: HashSet<_> = current_by_addr.keys().copied().collect();

        let removed: Vec<_> = current_addrs.difference(&new_addrs).copied().collect();
        let added: Vec<_> = new_addrs.difference(&current_addrs).copied().collect();
        let kept: Vec<_> = new_addrs.intersection(&current_addrs).copied().collect();

        let mut outcome = crate::node::UpdatePeersOutcome::default();

        for node_addr in &removed {
            if self.retry_pending.remove(node_addr).is_some() {
                debug!(
                    peer = %self.peer_display_name(node_addr),
                    "Dropping retry entry for peer removed from runtime peer list"
                );
            }
            self.peer_aliases.remove(node_addr);
            self.set_discovery_fallback_transit_allowed(*node_addr, false);
            outcome.removed += 1;
        }

        let mut auto_connect_refresh_configs = Vec::new();
        for node_addr in &kept {
            let new_pc = &new_by_addr[node_addr];
            let current_pc = &current_by_addr[node_addr];
            if new_pc.addresses != current_pc.addresses
                || new_pc.alias != current_pc.alias
                || new_pc.connect_policy != current_pc.connect_policy
                || new_pc.auto_reconnect != current_pc.auto_reconnect
                || new_pc.discovery_fallback_transit != current_pc.discovery_fallback_transit
            {
                outcome.updated += 1;
                self.set_discovery_fallback_transit_allowed(
                    *node_addr,
                    new_pc.discovery_fallback_transit,
                );
                if let Some(state) = self.retry_pending.get_mut(node_addr) {
                    state.peer_config = new_pc.clone();
                    state.retry_after_ms = Self::now_ms();
                }
                if let Some(alias) = new_pc.alias.clone() {
                    self.peer_aliases.insert(*node_addr, alias);
                }
                if new_pc.is_auto_connect() && !new_pc.addresses.is_empty() {
                    auto_connect_refresh_configs.push(new_pc.clone());
                }
            } else {
                outcome.unchanged += 1;
                self.set_discovery_fallback_transit_allowed(
                    *node_addr,
                    new_pc.discovery_fallback_transit,
                );
                if let Some(state) = self.retry_pending.get_mut(node_addr) {
                    state.peer_config = new_pc.clone();
                }
                if new_pc.is_auto_connect() && !new_pc.addresses.is_empty() {
                    auto_connect_refresh_configs.push(new_pc.clone());
                }
            }
        }

        let added_configs: Vec<crate::config::PeerConfig> = new_order
            .iter()
            .filter(|addr| added.contains(addr))
            .map(|addr| new_by_addr[addr].clone())
            .collect();

        // Replace the live config peer list before initiating connections so
        // any helper that consults `self.config.peers()` during the dial
        // (alias lookup, retry-state seeding) sees the new entries.
        self.config.peers = new_order
            .iter()
            .filter_map(|addr| new_by_addr.get(addr).cloned())
            .collect();
        self.configured_peer_send_weights = Self::configured_peer_send_weights(&self.config);

        for peer_config in added_configs {
            outcome.added += 1;
            let Ok(identity) = PeerIdentity::from_npub(&peer_config.npub) else {
                continue;
            };
            let name = peer_config
                .alias
                .clone()
                .unwrap_or_else(|| identity.short_npub());
            self.peer_aliases.insert(*identity.node_addr(), name);
            self.set_discovery_fallback_transit_allowed(
                *identity.node_addr(),
                peer_config.discovery_fallback_transit,
            );
            self.register_identity(*identity.node_addr(), identity.pubkey_full());

            if !peer_config.is_auto_connect() {
                continue;
            }

            match self
                .try_auto_connect_graph_session(&peer_config, identity)
                .await
            {
                Ok(true) => continue,
                Ok(false) => {}
                Err(err) => {
                    debug!(
                        npub = %peer_config.npub,
                        error = %err,
                        "Existing FIPS graph did not warm newly added peer"
                    );
                }
            }

            if let Err(e) = self.initiate_peer_connection(&peer_config).await {
                warn!(
                    npub = %peer_config.npub,
                    error = %e,
                    "Failed to initiate connection for newly added peer"
                );
                if let Ok(peer_identity) = PeerIdentity::from_npub(&peer_config.npub) {
                    self.schedule_retry_after_error(*peer_identity.node_addr(), Self::now_ms(), &e);
                }
                if matches!(e, crate::node::NodeError::NoTransportForType(_))
                    && let Some(bootstrap) = self.nostr_discovery.clone()
                {
                    bootstrap
                        .request_advert_stale_check(peer_config.npub.clone())
                        .await;
                }
            }
        }

        for peer_config in auto_connect_refresh_configs {
            let Ok(peer_identity) = PeerIdentity::from_npub(&peer_config.npub) else {
                continue;
            };
            let node_addr = *peer_identity.node_addr();

            if self.peers.contains_key(&node_addr) {
                match self
                    .initiate_active_peer_alternative_connection(&peer_config)
                    .await
                {
                    Ok(attempted) => {
                        if attempted {
                            debug!(
                                peer = %self.peer_display_name(&node_addr),
                                "Started non-disruptive alternate-path handshake for active peer"
                            );
                        }
                    }
                    Err(e) => {
                        debug!(
                            npub = %peer_config.npub,
                            error = %e,
                            "Active peer alternate-path refresh did not start"
                        );
                    }
                }
                continue;
            }

            match self
                .try_auto_connect_graph_session(&peer_config, peer_identity)
                .await
            {
                Ok(true) => continue,
                Ok(false) => {}
                Err(err) => {
                    debug!(
                        npub = %peer_config.npub,
                        error = %err,
                        "Existing FIPS graph did not warm refreshed peer"
                    );
                }
            }

            match self.initiate_peer_connection(&peer_config).await {
                Ok(()) => {
                    let hs_timeout_ms = self.config.node.rate_limit.handshake_timeout_secs * 1000;
                    if let Some(state) = self.retry_pending.get_mut(&node_addr) {
                        state.peer_config = peer_config;
                        state.retry_after_ms = Self::now_ms().saturating_add(hs_timeout_ms);
                    }
                }
                Err(e) => {
                    debug!(
                        npub = %peer_config.npub,
                        error = %e,
                        "Refreshed peer addresses did not initiate a direct connection"
                    );
                    self.schedule_retry_after_error(node_addr, Self::now_ms(), &e);
                }
            }
        }

        self.warm_auto_connect_graph_sessions().await;

        Ok(outcome)
    }

    pub(super) async fn initiate_peer_connections(&mut self) {
        // Build display name map from all configured peers (alias or short npub),
        // and pre-seed the identity cache from each peer's npub so that TUN packets
        // addressed to a configured peer can be dispatched (and trigger session
        // initiation) immediately on startup — without waiting for the link-layer
        // handshake to complete first.
        let peer_identities: Vec<(PeerIdentity, Option<String>)> = self
            .config
            .peers()
            .iter()
            .filter_map(|pc| {
                PeerIdentity::from_npub(&pc.npub)
                    .ok()
                    .map(|id| (id, pc.alias.clone()))
            })
            .collect();

        for (identity, alias) in peer_identities {
            let name = alias.unwrap_or_else(|| identity.short_npub());
            self.peer_aliases.insert(*identity.node_addr(), name);
            // Pre-seed identity cache. The parity may be wrong (npub is x-only)
            // but will be corrected to the real value when the peer is promoted
            // after a successful Noise handshake.
            self.register_identity(*identity.node_addr(), identity.pubkey_full());
        }

        // Collect peer configs to avoid borrow conflicts
        let peer_configs: Vec<_> = self.config.auto_connect_peers().cloned().collect();

        if peer_configs.is_empty() {
            debug!("No static peers configured");
            return;
        }

        debug!(
            count = peer_configs.len(),
            "Initiating static peer connections"
        );

        for peer_config in peer_configs {
            let peer_identity = match PeerIdentity::from_npub(&peer_config.npub) {
                Ok(identity) => identity,
                Err(_) => continue,
            };
            match self
                .try_auto_connect_graph_session(&peer_config, peer_identity)
                .await
            {
                Ok(true) => continue,
                Ok(false) => {}
                Err(err) => {
                    debug!(
                        npub = %peer_config.npub,
                        error = %err,
                        "Existing FIPS graph did not warm auto-connect peer"
                    );
                }
            }
            if let Err(e) = self.initiate_peer_connection(&peer_config).await {
                warn!(
                    npub = %peer_config.npub,
                    alias = ?peer_config.alias,
                    error = %e,
                    "Failed to initiate peer connection"
                );
                // Schedule a retry so transient address-resolution failures
                // (e.g. cached endpoints stale, NAT rebinds, all addresses
                // currently unreachable) recover without a daemon restart.
                if let Ok(peer_identity) = PeerIdentity::from_npub(&peer_config.npub) {
                    self.schedule_retry_after_error(*peer_identity.node_addr(), Self::now_ms(), &e);
                }
                // No-transport failures most often mean the cached overlay
                // advert is pointing at a dead post-NAT-rebind address. The
                // advert cache is read-only inside fetch_advert, so retries
                // would loop on the same dead address until expiry. Force a
                // re-fetch so the next retry tick picks up fresh endpoints.
                if matches!(e, crate::node::NodeError::NoTransportForType(_))
                    && let Some(bootstrap) = self.nostr_discovery.clone()
                {
                    bootstrap
                        .request_advert_stale_check(peer_config.npub.clone())
                        .await;
                }
            }
        }

        self.warm_auto_connect_graph_sessions().await;
    }

    pub(in crate::node) async fn try_auto_connect_graph_session(
        &mut self,
        peer_config: &PeerConfig,
        peer_identity: PeerIdentity,
    ) -> Result<bool, NodeError> {
        if !peer_config.is_auto_connect() {
            return Ok(false);
        }

        let peer_node_addr = *peer_identity.node_addr();
        if self
            .peers
            .get(&peer_node_addr)
            .is_some_and(|peer| peer.can_send())
        {
            return Ok(false);
        }
        if self.auto_connect_should_race_direct_path(peer_config) {
            return Ok(false);
        }
        if self
            .sessions
            .get(&peer_node_addr)
            .is_some_and(|entry| entry.is_established() || entry.is_initiating())
        {
            return Ok(true);
        }
        if self.find_next_hop(&peer_node_addr).is_none() {
            return Ok(false);
        }

        self.register_identity(peer_node_addr, peer_identity.pubkey_full());
        match self
            .initiate_session(peer_node_addr, peer_identity.pubkey_full())
            .await
        {
            Ok(()) => {
                debug!(
                    peer = %self.peer_display_name(&peer_node_addr),
                    "Warmed auto-connect peer session over existing FIPS graph"
                );
                Ok(true)
            }
            Err(NodeError::SendFailed { node_addr, reason })
                if node_addr == peer_node_addr && reason == "no route to destination" =>
            {
                self.maybe_initiate_lookup(&peer_node_addr).await;
                Ok(false)
            }
            Err(err) => Err(err),
        }
    }

    fn auto_connect_should_race_direct_path(&self, peer_config: &PeerConfig) -> bool {
        !peer_config.addresses.is_empty() || self.config.node.discovery.nostr.enabled
    }

    /// Initiate a connection to a single peer.
    ///
    /// Creates a link, starts the Noise handshake, and sends the first message.
    pub(super) async fn initiate_peer_connection(
        &mut self,
        peer_config: &crate::config::PeerConfig,
    ) -> Result<(), NodeError> {
        self.initiate_peer_connection_inner(peer_config).await
    }

    /// Initiate a connection from the retry path. Identical to
    /// [`initiate_peer_connection`] today — both paths fan out across every
    /// known address (explicit priority first, then freshness) in a single
    /// pass. The two entry points stay separate so callers can be distinguished
    /// in tracing.
    pub(super) async fn initiate_peer_retry_connection(
        &mut self,
        peer_config: &crate::config::PeerConfig,
    ) -> Result<(), NodeError> {
        self.initiate_peer_connection_inner(peer_config).await
    }

    pub(in crate::node) async fn initiate_active_peer_alternative_connection(
        &mut self,
        peer_config: &crate::config::PeerConfig,
    ) -> Result<bool, NodeError> {
        self.initiate_active_peer_alternative_connection_inner(peer_config, false)
            .await
    }

    pub(in crate::node) async fn initiate_active_peer_direct_refresh_connection(
        &mut self,
        peer_config: &crate::config::PeerConfig,
    ) -> Result<bool, NodeError> {
        self.initiate_active_peer_alternative_connection_inner(peer_config, true)
            .await
    }

    async fn initiate_active_peer_alternative_connection_inner(
        &mut self,
        peer_config: &crate::config::PeerConfig,
        allow_same_path_refresh: bool,
    ) -> Result<bool, NodeError> {
        let peer_identity =
            PeerIdentity::from_npub(&peer_config.npub).map_err(|e| NodeError::InvalidPeerNpub {
                npub: peer_config.npub.clone(),
                reason: e.to_string(),
            })?;
        let peer_node_addr = *peer_identity.node_addr();

        if !self.peers.contains_key(&peer_node_addr) {
            self.initiate_peer_connection(peer_config).await?;
            return Ok(true);
        }

        // Keep the current link live and race fresh concrete candidates.
        // Cross-connection resolution still decides which replacement link
        // wins if both peers try the same upgrade; the important part here is
        // that a stale path does not depend on the remote peer receiving our
        // hint first before either side attempts the better address.
        self.try_active_peer_alternative_addresses(
            peer_config,
            peer_identity,
            allow_same_path_refresh,
        )
        .await
    }

    async fn initiate_peer_connection_inner(
        &mut self,
        peer_config: &crate::config::PeerConfig,
    ) -> Result<(), NodeError> {
        // Parse the peer's npub to get their identity
        let peer_identity =
            PeerIdentity::from_npub(&peer_config.npub).map_err(|e| NodeError::InvalidPeerNpub {
                npub: peer_config.npub.clone(),
                reason: e.to_string(),
            })?;

        let peer_node_addr = *peer_identity.node_addr();

        // Check if peer already exists (fully authenticated)
        if self.peers.contains_key(&peer_node_addr) {
            debug!(
                npub = %peer_config.npub,
                "Peer already exists, skipping"
            );
            return Ok(());
        }

        self.try_peer_addresses(peer_config, peer_identity, true)
            .await
    }

    fn is_connecting_to_peer(&self, peer_node_addr: &NodeAddr) -> bool {
        self.connections.values().any(|conn| {
            conn.expected_identity()
                .map(|id| id.node_addr() == peer_node_addr)
                .unwrap_or(false)
        })
    }

    fn is_connecting_to_peer_on_path(
        &self,
        peer_node_addr: &NodeAddr,
        transport_id: TransportId,
        remote_addr: &TransportAddr,
    ) -> bool {
        self.connections.values().any(|conn| {
            conn.expected_identity()
                .map(|id| id.node_addr() == peer_node_addr)
                .unwrap_or(false)
                && conn.transport_id() == Some(transport_id)
                && conn.source_addr() == Some(remote_addr)
        }) || self.pending_connects.iter().any(|pending| {
            pending.peer_identity.node_addr() == peer_node_addr
                && pending.transport_id == transport_id
                && &pending.remote_addr == remote_addr
        })
    }

    pub(in crate::node) fn should_warm_auto_connect_session(
        &self,
        peer_node_addr: &NodeAddr,
    ) -> bool {
        if self
            .peers
            .get(peer_node_addr)
            .is_some_and(|peer| peer.can_send())
            || self
                .sessions
                .get(peer_node_addr)
                .is_some_and(|entry| entry.is_established())
        {
            return false;
        }

        self.config.peers().iter().any(|peer| {
            peer.is_auto_connect()
                && PeerIdentity::from_npub(&peer.npub)
                    .map(|identity| identity.node_addr() == peer_node_addr)
                    .unwrap_or(false)
        })
    }

    pub(in crate::node) async fn warm_auto_connect_graph_sessions(&mut self) -> usize {
        if !self.peers.values().any(|peer| peer.can_send()) {
            return 0;
        }

        let mut budget = self.graph_session_warmup_budget();
        if budget == 0 {
            return 0;
        }

        let peer_identities: Vec<_> = self
            .config
            .auto_connect_peers()
            .filter_map(|peer| PeerIdentity::from_npub(&peer.npub).ok())
            .collect();

        let mut warmed = 0;
        for identity in peer_identities {
            if budget == 0 {
                break;
            }

            let peer_node_addr = *identity.node_addr();
            if peer_node_addr == *self.identity.node_addr()
                || !self.should_warm_auto_connect_session(&peer_node_addr)
                || self
                    .sessions
                    .get(&peer_node_addr)
                    .is_some_and(|entry| entry.is_initiating())
            {
                continue;
            }

            self.register_identity(peer_node_addr, identity.pubkey_full());

            if self.find_next_hop(&peer_node_addr).is_some() {
                match self
                    .initiate_session(peer_node_addr, identity.pubkey_full())
                    .await
                {
                    Ok(()) => {
                        warmed += 1;
                        budget = budget.saturating_sub(1);
                        debug!(
                            peer = %self.peer_display_name(&peer_node_addr),
                            "Warmed auto-connect peer session over existing FIPS graph"
                        );
                    }
                    Err(NodeError::SendFailed { node_addr, reason })
                        if node_addr == peer_node_addr && reason == "no route to destination" =>
                    {
                        self.maybe_initiate_lookup(&peer_node_addr).await;
                        warmed += 1;
                        budget = budget.saturating_sub(1);
                    }
                    Err(err) => {
                        debug!(
                            peer = %self.peer_display_name(&peer_node_addr),
                            error = %err,
                            "Failed to warm auto-connect peer session"
                        );
                    }
                }
            } else {
                self.maybe_initiate_lookup(&peer_node_addr).await;
                warmed += 1;
                budget = budget.saturating_sub(1);
            }
        }

        warmed
    }

    pub(in crate::node) fn graph_session_warmup_budget(&self) -> usize {
        let max_destinations = self.config.node.session.pending_max_destinations;
        if max_destinations == 0 {
            return 0;
        }

        let pending_sessions = self
            .sessions
            .values()
            .filter(|entry| !entry.is_established())
            .count();
        let pending_total = pending_sessions.saturating_add(self.pending_lookups.len());
        max_destinations
            .saturating_sub(pending_total)
            .min(MAX_AUTO_CONNECT_GRAPH_WARMUPS_PER_TICK)
    }

    fn outbound_handshake_slots(&self) -> usize {
        let used = self
            .connections
            .len()
            .saturating_add(self.pending_connects.len());
        if self.max_connections == 0 {
            usize::MAX
        } else {
            self.max_connections.saturating_sub(used)
        }
    }

    fn outbound_link_slots(&self) -> usize {
        if self.max_links == 0 {
            usize::MAX
        } else {
            self.max_links.saturating_sub(self.links.len())
        }
    }

    fn path_candidate_attempt_budget(&self, peer_node_addr: &NodeAddr) -> usize {
        if !self.peers.contains_key(peer_node_addr)
            && self.max_peers > 0
            && self.peers.len() >= self.max_peers
        {
            return 0;
        }

        let in_flight_for_peer = self
            .connections
            .values()
            .filter(|conn| {
                conn.expected_identity()
                    .map(|id| id.node_addr() == peer_node_addr)
                    .unwrap_or(false)
            })
            .count()
            .saturating_add(
                self.pending_connects
                    .iter()
                    .filter(|pending| pending.peer_identity.node_addr() == peer_node_addr)
                    .count(),
            );

        self.outbound_handshake_slots()
            .min(self.outbound_link_slots())
            .min(MAX_PARALLEL_PATH_CANDIDATES_PER_PEER.saturating_sub(in_flight_for_peer))
    }

    fn reclaim_lower_priority_inflight_candidate_for_peer(
        &mut self,
        peer_node_addr: &NodeAddr,
        candidate: &PeerAddress,
    ) -> bool {
        const UNKNOWN_PATH_PRIORITY: u16 = u8::MAX as u16 + 1;

        let Some((candidate_transport_id, candidate_addr)) =
            self.resolve_peer_address_for_match(candidate)
        else {
            return false;
        };
        let Some(candidate_priority) =
            self.configured_path_priority(peer_node_addr, candidate_transport_id, &candidate_addr)
        else {
            return false;
        };
        let candidate_priority = u16::from(candidate_priority);

        let victim = self
            .connections
            .iter()
            .filter_map(|(link_id, conn)| {
                let identity = conn.expected_identity()?;
                if identity.node_addr() != peer_node_addr {
                    return None;
                }
                let transport_id = conn.transport_id()?;
                let remote_addr = conn.source_addr()?;
                if transport_id == candidate_transport_id && remote_addr == &candidate_addr {
                    return None;
                }
                let priority = self
                    .configured_path_priority(peer_node_addr, transport_id, remote_addr)
                    .map(u16::from)
                    .unwrap_or(UNKNOWN_PATH_PRIORITY);
                (priority > candidate_priority).then_some((
                    *link_id,
                    priority,
                    conn.started_at(),
                    transport_id,
                    remote_addr.clone(),
                ))
            })
            .max_by_key(|(_, priority, started_at, _, _)| {
                (*priority, std::cmp::Reverse(*started_at))
            });

        let Some((link_id, victim_priority, _, victim_transport_id, victim_addr)) = victim else {
            return false;
        };

        let Some(conn) = self.connections.remove(&link_id) else {
            return false;
        };
        if let Some(idx) = conn.our_index()
            && let Some(transport_id) = conn.transport_id()
        {
            self.pending_outbound.remove(&(transport_id, idx.as_u32()));
            let _ = self.index_allocator.free(idx);
        }
        self.remove_link(&link_id);
        self.cleanup_bootstrap_transport_if_unused(victim_transport_id);

        debug!(
            peer = %self.peer_display_name(peer_node_addr),
            candidate_transport_id = %candidate_transport_id,
            candidate_addr = %candidate_addr,
            candidate_priority,
            victim_link_id = %link_id,
            victim_transport_id = %victim_transport_id,
            victim_addr = %victim_addr,
            victim_priority,
            "Reclaimed lower-priority in-flight candidate slot for configured direct path"
        );

        true
    }

    fn discovery_connect_budget(&self) -> usize {
        self.outbound_handshake_slots()
            .min(self.outbound_link_slots())
            .min(MAX_DISCOVERY_CONNECTS_PER_TICK)
    }

    /// Find a UDP transport whose bound socket can send to `remote_addr`.
    ///
    /// LAN discovery can surface both IPv4 and IPv6 addresses for the same
    /// service. A wildcard IPv4 socket cannot send to an IPv6 link-local
    /// target, and vice versa, so callers must choose by socket family rather
    /// than by transport type alone.
    fn find_udp_transport_for_remote_addr(
        &self,
        remote_addr: SocketAddr,
    ) -> Option<(TransportId, SocketAddr)> {
        self.transports
            .iter()
            .filter(|(id, handle)| {
                handle.transport_type().name == "udp"
                    && handle.is_operational()
                    && !self.bootstrap_transports.contains(id)
            })
            .filter_map(|(id, handle)| {
                let local_addr = handle.local_addr()?;
                socket_addr_families_compatible(local_addr, remote_addr)
                    .then_some((*id, local_addr))
            })
            .min_by_key(|(id, _)| id.as_u32())
    }

    pub(super) fn transport_discovery_candidate(
        &self,
        discovered_transport_id: TransportId,
        discovered_addr: TransportAddr,
    ) -> Option<(TransportId, TransportAddr, &'static str)> {
        let transport = self.transports.get(&discovered_transport_id)?;
        let transport_name = transport.transport_type().name;

        if transport_name != "udp" {
            return Some((discovered_transport_id, discovered_addr, transport_name));
        }

        let Some(remote_socket_addr) = discovered_addr
            .as_str()
            .and_then(|addr| addr.parse::<SocketAddr>().ok())
        else {
            if self.bootstrap_transports.contains(&discovered_transport_id) {
                debug!(
                    transport_id = %discovered_transport_id,
                    remote_addr = %discovered_addr,
                    "transport discovery: skip non-numeric UDP address from bootstrap transport"
                );
                return None;
            }
            return Some((discovered_transport_id, discovered_addr, transport_name));
        };

        let Some((transport_id, local_addr)) =
            self.find_udp_transport_for_remote_addr(remote_socket_addr)
        else {
            debug!(
                transport_id = %discovered_transport_id,
                remote_addr = %discovered_addr,
                "transport discovery: skip UDP peer with no compatible local socket"
            );
            return None;
        };

        if transport_id != discovered_transport_id {
            debug!(
                discovered_transport_id = %discovered_transport_id,
                selected_transport_id = %transport_id,
                local_addr = %local_addr,
                remote_addr = %remote_socket_addr,
                "transport discovery: selected compatible UDP transport"
            );
        }

        Some((
            transport_id,
            TransportAddr::from_socket_addr(remote_socket_addr),
            transport_name,
        ))
    }

    fn peer_address_string_for_transport_candidate(
        &self,
        transport_id: TransportId,
        transport_name: &str,
        remote_addr: &TransportAddr,
    ) -> String {
        #[cfg(not(any(target_os = "linux", target_os = "macos")))]
        let _ = (transport_id, transport_name);

        #[cfg(any(target_os = "linux", target_os = "macos"))]
        if transport_name == "ethernet"
            && remote_addr.as_bytes().len() == 6
            && let Some(interface) = self
                .transports
                .get(&transport_id)
                .and_then(|transport| transport.interface_name())
        {
            let mut mac = [0u8; 6];
            mac.copy_from_slice(remote_addr.as_bytes());
            return format!(
                "{interface}/{}",
                crate::transport::ethernet::format_mac(&mac)
            );
        }

        remote_addr.to_string()
    }

    fn resolve_peer_address_for_match(
        &self,
        candidate: &PeerAddress,
    ) -> Option<(TransportId, TransportAddr)> {
        if candidate.transport == "udp" && candidate.addr.eq_ignore_ascii_case("nat") {
            return None;
        }

        if candidate.transport == "ethernet" {
            return self.resolve_ethernet_addr(&candidate.addr).ok();
        }

        if candidate.transport == "ble" {
            #[cfg(bluer_available)]
            {
                return self.resolve_ble_addr(&candidate.addr).ok();
            }
            #[cfg(not(bluer_available))]
            {
                return None;
            }
        }

        let transport_id = if candidate.transport == "udp"
            && let Ok(remote_socket_addr) = candidate.addr.parse::<SocketAddr>()
        {
            self.find_udp_transport_for_remote_addr(remote_socket_addr)
                .map(|(id, _)| id)?
        } else {
            self.find_transport_for_type(&candidate.transport)?
        };

        Some((transport_id, TransportAddr::from_string(&candidate.addr)))
    }

    /// Initiate a connection to a peer on a specific transport and address.
    ///
    /// For connectionless transports (UDP, Ethernet): allocates a link, starts
    /// the Noise IK handshake, sends msg1, and registers the connection for
    /// msg2 dispatch.
    ///
    /// For connection-oriented transports (TCP, Tor): allocates a link and
    /// starts a non-blocking transport connect. The handshake is deferred
    /// until the transport connection is established — the tick handler
    /// polls `connection_state()` and initiates the handshake when ready.
    pub(super) async fn initiate_connection(
        &mut self,
        transport_id: TransportId,
        remote_addr: TransportAddr,
        peer_identity: PeerIdentity,
    ) -> Result<(), NodeError> {
        let peer_node_addr = *peer_identity.node_addr();

        if self.is_connecting_to_peer_on_path(&peer_node_addr, transport_id, &remote_addr) {
            debug!(
                peer = %self.peer_display_name(&peer_node_addr),
                transport_id = %transport_id,
                remote_addr = %remote_addr,
                "Connection already in progress for candidate path"
            );
            return Ok(());
        }

        if self.outbound_handshake_slots() == 0 {
            return Err(NodeError::MaxConnectionsExceeded {
                max: self.max_connections,
            });
        }

        if self.outbound_link_slots() == 0 {
            return Err(NodeError::MaxLinksExceeded {
                max: self.max_links,
            });
        }

        if !self.peers.contains_key(&peer_node_addr)
            && self.max_peers > 0
            && self.peers.len() >= self.max_peers
        {
            return Err(NodeError::MaxPeersExceeded {
                max: self.max_peers,
            });
        }

        self.authorize_peer(
            &peer_identity,
            PeerAclContext::OutboundConnect,
            transport_id,
            &remote_addr,
        )?;

        let is_connection_oriented = self
            .transports
            .get(&transport_id)
            .map(|t| t.transport_type().connection_oriented)
            .unwrap_or(false);

        // Allocate link ID and create link
        let link_id = self.allocate_link_id();

        let link = if is_connection_oriented {
            Link::new(
                link_id,
                transport_id,
                remote_addr.clone(),
                LinkDirection::Outbound,
                Duration::from_millis(self.config.node.base_rtt_ms),
            )
        } else {
            Link::connectionless(
                link_id,
                transport_id,
                remote_addr.clone(),
                LinkDirection::Outbound,
                Duration::from_millis(self.config.node.base_rtt_ms),
            )
        };

        self.links.insert(link_id, link);

        // Add reverse lookup for packet dispatch
        self.addr_to_link
            .insert((transport_id, remote_addr.clone()), link_id);

        if is_connection_oriented {
            // Connection-oriented: start non-blocking connect, defer handshake
            if let Some(transport) = self.transports.get(&transport_id) {
                match transport.connect(&remote_addr).await {
                    Ok(()) => {
                        debug!(
                            peer = %self.peer_display_name(&peer_node_addr),
                            transport_id = %transport_id,
                            remote_addr = %remote_addr,
                            link_id = %link_id,
                            "Transport connect initiated (non-blocking)"
                        );
                        self.pending_connects.push(super::PendingConnect {
                            link_id,
                            transport_id,
                            remote_addr,
                            peer_identity,
                        });
                    }
                    Err(e) => {
                        // Clean up link
                        self.links.remove(&link_id);
                        self.addr_to_link.remove(&(transport_id, remote_addr));
                        return Err(NodeError::from_transport_error(e));
                    }
                }
            }
            Ok(())
        } else {
            // Connectionless: proceed with immediate handshake
            self.start_handshake(link_id, transport_id, remote_addr, peer_identity)
                .await
        }
    }

    /// Start the Noise handshake on a link and send msg1.
    ///
    /// Called immediately for connectionless transports, or after the
    /// transport connection is established for connection-oriented transports.
    pub(super) async fn start_handshake(
        &mut self,
        link_id: LinkId,
        transport_id: TransportId,
        remote_addr: TransportAddr,
        peer_identity: PeerIdentity,
    ) -> Result<(), NodeError> {
        let peer_node_addr = *peer_identity.node_addr();

        // Create connection in handshake phase (outbound knows expected identity)
        let current_time_ms = Self::now_ms();
        let mut connection = PeerConnection::outbound(link_id, peer_identity, current_time_ms);

        // Allocate a session index for this handshake
        let our_index = match self.index_allocator.allocate() {
            Ok(idx) => idx,
            Err(e) => {
                // Clean up the link we just created
                self.links.remove(&link_id);
                self.addr_to_link.remove(&(transport_id, remote_addr));
                return Err(NodeError::IndexAllocationFailed(e.to_string()));
            }
        };

        // Start the Noise handshake and get message 1
        let our_keypair = self.identity.keypair();
        let noise_msg1 =
            match connection.start_handshake(our_keypair, self.startup_epoch, current_time_ms) {
                Ok(msg) => msg,
                Err(e) => {
                    // Clean up the index and link
                    let _ = self.index_allocator.free(our_index);
                    self.links.remove(&link_id);
                    self.addr_to_link.remove(&(transport_id, remote_addr));
                    return Err(NodeError::HandshakeFailed(e.to_string()));
                }
            };

        // Set index and transport info on the connection
        connection.set_our_index(our_index);
        connection.set_transport_id(transport_id);
        connection.set_source_addr(remote_addr.clone());

        // Build wire format msg1: [0x01][sender_idx:4 LE][noise_msg1:82]
        let wire_msg1 = build_msg1(our_index, &noise_msg1);

        debug!(
            peer = %self.peer_display_name(&peer_node_addr),
            transport_id = %transport_id,
            remote_addr = %remote_addr,
            link_id = %link_id,
            our_index = %our_index,
            "Connection initiated"
        );

        // Store msg1 for resend and schedule first resend
        let resend_interval = self.config.node.rate_limit.handshake_resend_interval_ms;
        connection.set_handshake_msg1(wire_msg1.clone(), current_time_ms + resend_interval);

        // Track in pending_outbound for msg2 dispatch
        self.pending_outbound
            .insert((transport_id, our_index.as_u32()), link_id);
        self.connections.insert(link_id, connection);

        // Send the wire format handshake message. If the very first send fails
        // synchronously (for example an IPv6 candidate on an IPv4-only UDP
        // socket), undo this candidate so the caller can try the next address
        // in the same dial pass.
        let send_result = match self.transports.get(&transport_id) {
            Some(transport) => Some(transport.send(&remote_addr, &wire_msg1).await),
            None => None,
        };
        match send_result {
            Some(send_result) => {
                self.note_local_send_outcome(&peer_node_addr, &send_result);
                match send_result {
                    Ok(bytes) => {
                        debug!(
                            link_id = %link_id,
                            our_index = %our_index,
                            bytes,
                            "Sent Noise handshake message 1 (wire format)"
                        );
                    }
                    Err(e) => {
                        warn!(
                            link_id = %link_id,
                            transport_id = %transport_id,
                            remote_addr = %remote_addr,
                            our_index = %our_index,
                            error = %e,
                            "Failed to send handshake message"
                        );
                        self.pending_outbound
                            .remove(&(transport_id, our_index.as_u32()));
                        self.connections.remove(&link_id);
                        self.links.remove(&link_id);
                        self.addr_to_link
                            .remove(&(transport_id, remote_addr.clone()));
                        let _ = self.index_allocator.free(our_index);
                        return Err(NodeError::from_transport_error(e));
                    }
                }
            }
            None => {
                self.pending_outbound
                    .remove(&(transport_id, our_index.as_u32()));
                self.connections.remove(&link_id);
                self.links.remove(&link_id);
                self.addr_to_link
                    .remove(&(transport_id, remote_addr.clone()));
                let _ = self.index_allocator.free(our_index);
                return Err(NodeError::TransportError(format!(
                    "transport {transport_id} disappeared before first handshake send"
                )));
            }
        }

        Ok(())
    }

    /// Poll all transports for discovered peers and auto-connect.
    ///
    /// Called from the tick handler. Iterates operational transports,
    /// drains their discovery buffers, and initiates connections to
    /// newly discovered peers (if auto_connect is enabled).
    pub(super) async fn poll_transport_discovery(&mut self) {
        // Collect discoveries first to avoid borrow conflict with self
        let mut to_connect = Vec::new();
        let mut queued_per_peer: HashMap<NodeAddr, usize> = HashMap::new();
        let mut connect_budget = self.discovery_connect_budget();
        let mut skipped_budget = 0usize;

        for transport in self.transports.values() {
            if !transport.is_operational() {
                continue;
            }
            if !transport.auto_connect() {
                // Still drain the buffer so it doesn't grow unbounded
                let _ = transport.discover();
                continue;
            }
            let discovered = match transport.discover() {
                Ok(peers) => peers,
                Err(_) => continue,
            };
            for peer in discovered {
                let discovered_transport_id = peer.transport_id;
                let pubkey = match peer.pubkey_hint {
                    Some(pk) => pk,
                    None => continue,
                };
                let identity = PeerIdentity::from_pubkey(pubkey);
                let node_addr = *identity.node_addr();

                // Skip self
                if node_addr == *self.identity.node_addr() {
                    continue;
                }

                let Some((candidate_transport_id, remote_addr, transport_name)) =
                    self.transport_discovery_candidate(discovered_transport_id, peer.addr)
                else {
                    continue;
                };

                if self.peers.contains_key(&node_addr) {
                    let candidate = PeerAddress::new(
                        transport_name,
                        self.peer_address_string_for_transport_candidate(
                            candidate_transport_id,
                            transport_name,
                            &remote_addr,
                        ),
                    );
                    if self.active_peer_candidate_is_fresh_enough_to_skip(
                        &node_addr,
                        std::slice::from_ref(&candidate),
                    ) {
                        continue;
                    }
                    if self.is_connecting_to_peer_on_path(
                        &node_addr,
                        candidate_transport_id,
                        &remote_addr,
                    ) {
                        continue;
                    }
                    let queued_for_peer = queued_per_peer.get(&node_addr).copied().unwrap_or(0);
                    if connect_budget == 0
                        || self
                            .path_candidate_attempt_budget(&node_addr)
                            .saturating_sub(queued_for_peer)
                            == 0
                    {
                        skipped_budget = skipped_budget.saturating_add(1);
                        continue;
                    }
                    to_connect.push((candidate_transport_id, remote_addr, identity, true));
                    *queued_per_peer.entry(node_addr).or_default() += 1;
                    connect_budget = connect_budget.saturating_sub(1);
                    continue;
                }

                if self.is_connecting_to_peer_on_path(
                    &node_addr,
                    candidate_transport_id,
                    &remote_addr,
                ) {
                    continue;
                }

                let queued_for_peer = queued_per_peer.get(&node_addr).copied().unwrap_or(0);
                if connect_budget == 0
                    || self
                        .path_candidate_attempt_budget(&node_addr)
                        .saturating_sub(queued_for_peer)
                        == 0
                {
                    skipped_budget = skipped_budget.saturating_add(1);
                    continue;
                }
                to_connect.push((candidate_transport_id, remote_addr, identity, false));
                *queued_per_peer.entry(node_addr).or_default() += 1;
                connect_budget = connect_budget.saturating_sub(1);
            }
        }

        if skipped_budget > 0 {
            debug!(
                skipped = skipped_budget,
                queued = to_connect.len(),
                "Transport discovery connect budget exhausted"
            );
        }

        for (transport_id, remote_addr, identity, active_refresh) in to_connect {
            info!(
                peer = %self.peer_display_name(identity.node_addr()),
                transport_id = %transport_id,
                remote_addr = %remote_addr,
                active_refresh,
                "Auto-connecting to discovered peer"
            );
            if let Err(e) = self
                .initiate_connection(transport_id, remote_addr, identity)
                .await
            {
                warn!(error = %e, "Failed to auto-connect to discovered peer");
            }
        }
    }

    pub(super) async fn poll_nostr_discovery(&mut self) {
        let Some(bootstrap) = self.nostr_discovery.clone() else {
            return;
        };

        bootstrap.set_outbound_admission(self.open_discovery_outbound_admission_check());
        bootstrap.set_direct_refresh_admission(self.outbound_direct_refresh_admission_check());

        self.drain_nostr_mesh_signals(&bootstrap).await;

        for event in bootstrap.drain_events().await {
            match event {
                BootstrapEvent::Established { traversal } => {
                    let active_refresh = PeerIdentity::from_npub(&traversal.peer_npub)
                        .ok()
                        .is_some_and(|identity| self.peers.contains_key(identity.node_addr()));
                    let admission_allowed = if active_refresh {
                        self.outbound_direct_refresh_admission_check()
                    } else {
                        self.outbound_admission_check()
                    };
                    if !admission_allowed {
                        debug!(
                            peer_npub = %traversal.peer_npub,
                            peers = self.peers.len(),
                            max_peers = self.max_peers,
                            active_refresh,
                            "Dropping established NAT traversal: at capacity"
                        );
                        continue;
                    }
                    let peer_npub = traversal.peer_npub.clone();
                    match self.adopt_established_traversal(traversal).await {
                        Ok(_) => {
                            info!(peer_npub = %peer_npub, "Adopted NAT traversal socket");
                        }
                        Err(err) => {
                            warn!(peer_npub = %peer_npub, error = %err, "Failed to adopt NAT traversal");
                            if let Ok(peer_identity) = PeerIdentity::from_npub(&peer_npub) {
                                self.schedule_retry(*peer_identity.node_addr(), Self::now_ms());
                            }
                        }
                    }
                }
                BootstrapEvent::Failed {
                    peer_config,
                    reason,
                } => {
                    let peer_identity = match PeerIdentity::from_npub(&peer_config.npub) {
                        Ok(identity) => identity,
                        Err(_) => continue,
                    };
                    let node_addr = *peer_identity.node_addr();
                    let now_ms = Self::now_ms();
                    if self.peers.contains_key(&node_addr) {
                        if self.active_peer_should_keep_direct_retry(&node_addr, &peer_config) {
                            let decision =
                                bootstrap.record_traversal_failure(&peer_config.npub, now_ms);
                            if decision.should_warn {
                                warn!(
                                    npub = %peer_config.npub,
                                    error = %reason,
                                    consecutive_failures = decision.consecutive_failures,
                                    cooldown_secs = decision
                                        .cooldown_until_ms
                                        .map(|t| t.saturating_sub(now_ms) / 1000),
                                    "Direct-path NAT traversal upgrade failed"
                                );
                            } else {
                                debug!(
                                    npub = %peer_config.npub,
                                    error = %reason,
                                    consecutive_failures = decision.consecutive_failures,
                                    "Direct-path NAT traversal upgrade failed (suppressed by warn-rate-limit)"
                                );
                            }
                            if decision.crossed_threshold {
                                bootstrap
                                    .request_advert_stale_check(peer_config.npub.clone())
                                    .await;
                            }
                            self.schedule_link_dead_reprobe(node_addr, now_ms);
                        } else {
                            debug!(
                                npub = %peer_config.npub,
                                error = %reason,
                                "Ignoring failed NAT traversal for already-connected peer on fresh direct path"
                            );
                        }
                        continue;
                    }
                    if self.is_connecting_to_peer(&node_addr) {
                        debug!(
                            npub = %peer_config.npub,
                            error = %reason,
                            "Ignoring failed NAT traversal while peer handshake is already in progress"
                        );
                        continue;
                    }

                    let decision = bootstrap.record_traversal_failure(&peer_config.npub, now_ms);
                    if decision.should_warn {
                        warn!(
                            npub = %peer_config.npub,
                            error = %reason,
                            consecutive_failures = decision.consecutive_failures,
                            cooldown_secs = decision
                                .cooldown_until_ms
                                .map(|t| t.saturating_sub(now_ms) / 1000),
                            "NAT traversal failed"
                        );
                    } else {
                        debug!(
                            npub = %peer_config.npub,
                            error = %reason,
                            consecutive_failures = decision.consecutive_failures,
                            "NAT traversal failed (suppressed by warn-rate-limit)"
                        );
                    }

                    // B6: stale-advert eviction on the streak-threshold
                    // crossing. Fire-and-forget; the outcome is logged so
                    // operators can see when peers get cleaned up.
                    if decision.crossed_threshold {
                        bootstrap
                            .request_advert_stale_check(peer_config.npub.clone())
                            .await;
                    }

                    if self
                        .try_peer_addresses(&peer_config, peer_identity, false)
                        .await
                        .is_ok()
                    {
                        continue;
                    }

                    self.schedule_retry(node_addr, now_ms);
                    if self.nostr_cooldown_applies_to_peer_config(&peer_config)
                        && let Some(cooldown_until_ms) = decision.cooldown_until_ms
                        && let Some(state) = self.retry_pending.get_mut(&node_addr)
                    {
                        // Push the next retry past the cooldown so the
                        // open-discovery sweep doesn't re-enqueue and the
                        // per-attempt backoff doesn't fire sooner.
                        state.retry_after_ms = state.retry_after_ms.max(cooldown_until_ms);
                    }
                }
            }
        }

        self.maybe_run_startup_open_discovery_sweep(&bootstrap)
            .await;
        self.queue_open_discovery_retries(&bootstrap).await;
        self.queue_active_fallback_direct_retries(&bootstrap);

        // Advert refresh can touch STUN/public-endpoint discovery on some
        // configs. Drain traversal events and queue direct retries first so a
        // slow refresh cannot delay path recovery work already waiting on us.
        if let Err(err) = self.refresh_overlay_advert(&bootstrap).await {
            debug!(error = %err, "Failed to refresh local Nostr overlay advert");
        }
    }

    async fn drain_nostr_mesh_signals(&mut self, bootstrap: &std::sync::Arc<NostrDiscovery>) {
        let mut deferred = Vec::new();

        for signal in bootstrap.drain_mesh_signals().await {
            let (peer_npub, msg_type, payload) = match &signal {
                MeshTraversalSignal::Offer { peer_npub, offer } => {
                    let payload = match serde_json::to_vec(&offer) {
                        Ok(payload) => payload,
                        Err(error) => {
                            debug!(
                                peer = %peer_npub,
                                error = %error,
                                "Failed to encode mesh traversal offer"
                            );
                            continue;
                        }
                    };
                    (
                        peer_npub.clone(),
                        SessionMessageType::TraversalOffer.to_byte(),
                        payload,
                    )
                }
                MeshTraversalSignal::Answer { peer_npub, answer } => {
                    let payload = match serde_json::to_vec(&answer) {
                        Ok(payload) => payload,
                        Err(error) => {
                            debug!(
                                peer = %peer_npub,
                                error = %error,
                                "Failed to encode mesh traversal answer"
                            );
                            continue;
                        }
                    };
                    (
                        peer_npub.clone(),
                        SessionMessageType::TraversalAnswer.to_byte(),
                        payload,
                    )
                }
            };

            let peer_identity = match PeerIdentity::from_npub(&peer_npub) {
                Ok(identity) => identity,
                Err(error) => {
                    debug!(
                        peer = %peer_npub,
                        error = %error,
                        "Cannot send mesh traversal signal to invalid peer npub"
                    );
                    continue;
                }
            };
            let peer_addr = *peer_identity.node_addr();
            match self
                .mesh_signal_session_action(peer_addr, peer_identity.pubkey_full())
                .await
            {
                MeshSignalSessionAction::Send => {}
                MeshSignalSessionAction::Defer => {
                    deferred.push(signal);
                    continue;
                }
                MeshSignalSessionAction::Drop => continue,
            }

            if let Err(error) = self.send_session_msg(&peer_addr, msg_type, &payload).await {
                debug!(
                    peer = %self.peer_display_name(&peer_addr),
                    error = %error,
                    "Failed to send mesh traversal signal"
                );
            }
        }

        for signal in deferred {
            bootstrap.requeue_mesh_signal(signal);
        }
    }

    async fn mesh_signal_session_action(
        &mut self,
        peer_addr: NodeAddr,
        peer_pubkey: PublicKey,
    ) -> MeshSignalSessionAction {
        if let Some(entry) = self.sessions.get(&peer_addr) {
            if entry.is_established() {
                return MeshSignalSessionAction::Send;
            }
            if entry.is_initiating() || entry.is_awaiting_msg3() {
                debug!(
                    peer = %self.peer_display_name(&peer_addr),
                    "Deferring mesh traversal signal until end-to-end session is established"
                );
                return MeshSignalSessionAction::Defer;
            }
        }

        if self.find_next_hop(&peer_addr).is_none() {
            debug!(
                peer = %self.peer_display_name(&peer_addr),
                "Cannot warm mesh traversal signal session without a FIPS route"
            );
            self.maybe_initiate_lookup(&peer_addr).await;
            return MeshSignalSessionAction::Drop;
        }

        self.register_identity(peer_addr, peer_pubkey);
        match self.initiate_session(peer_addr, peer_pubkey).await {
            Ok(()) => {
                debug!(
                    peer = %self.peer_display_name(&peer_addr),
                    "Warming end-to-end session for mesh traversal signal"
                );
                MeshSignalSessionAction::Defer
            }
            Err(NodeError::SendFailed { node_addr, reason })
                if node_addr == peer_addr && reason == "no route to destination" =>
            {
                debug!(
                    peer = %self.peer_display_name(&peer_addr),
                    "Cannot warm mesh traversal signal session without a FIPS route"
                );
                self.maybe_initiate_lookup(&peer_addr).await;
                MeshSignalSessionAction::Drop
            }
            Err(error) => {
                debug!(
                    peer = %self.peer_display_name(&peer_addr),
                    error = %error,
                    "Failed to warm end-to-end session for mesh traversal signal"
                );
                MeshSignalSessionAction::Drop
            }
        }
    }

    /// Resolve the LAN-only discovery scope. Applications with explicit
    /// connectivity config can set `node.discovery.lan.scope` without
    /// changing the public Nostr discovery `app` tag. The older fallback
    /// extracts a scope from the Nostr app tag used by default scoped
    /// discovery.
    pub(super) fn lan_discovery_scope(&self) -> Option<String> {
        if let Some(scope) = self.config.node.discovery.lan.scope.as_deref() {
            let scope = scope.trim();
            if !scope.is_empty() {
                return Some(scope.to_string());
            }
        }

        let app = self.config.node.discovery.nostr.app.trim();
        if app.is_empty() {
            return None;
        }
        if let Some(rest) = app.strip_prefix("fips-overlay-v1:") {
            let scope = rest.trim();
            if scope.is_empty() {
                None
            } else {
                Some(scope.to_string())
            }
        } else {
            Some(app.to_string())
        }
    }

    pub(super) fn start_local_instance_discovery(&mut self) {
        if !self.config.node.discovery.local.enabled {
            return;
        }
        let Some(scope) = self.lan_discovery_scope() else {
            debug!("local instance discovery not started: no discovery scope");
            return;
        };
        let now_ms = Self::now_ms();
        match crate::discovery::local::LocalInstanceRegistry::new(
            self.identity.npub(),
            scope,
            &self.config.node.discovery.local,
            now_ms,
        ) {
            Ok(registry) => {
                self.local_instance_registry = Some(registry);
                self.local_instance_started_at_ms = Some(now_ms);
                self.last_local_instance_publish_ms = None;
                self.last_local_instance_scan_ms = None;
                self.publish_local_instance_record(now_ms);
                info!("Same-host FIPS instance discovery enabled");
            }
            Err(crate::discovery::local::LocalInstanceRegistryError::Disabled) => {
                debug!("same-host FIPS instance discovery disabled");
            }
            Err(err) => {
                debug!(error = %err, "same-host FIPS instance discovery not started");
            }
        }
    }

    fn local_instance_contacts(&self) -> Vec<crate::discovery::local::LocalInstanceContact> {
        let mut contacts = Vec::new();
        for handle in self.transports.values() {
            if !handle.is_operational() || !handle.accept_connections() {
                continue;
            }
            let transport = handle.transport_type().name;
            if transport != "udp" && transport != "tcp" {
                continue;
            }
            let Some(local_addr) = handle.local_addr() else {
                continue;
            };
            let Some(contact) =
                crate::discovery::local::contact_for_transport_addr(transport, local_addr)
            else {
                continue;
            };
            if contacts
                .iter()
                .any(|existing: &crate::discovery::local::LocalInstanceContact| {
                    existing.transport == contact.transport && existing.addr == contact.addr
                })
            {
                continue;
            }
            contacts.push(contact);
        }
        contacts
    }

    fn publish_local_instance_record(&mut self, now_ms: u64) {
        let Some(registry) = self.local_instance_registry.clone() else {
            return;
        };
        let contacts = self.local_instance_contacts();
        match registry.publish(contacts, now_ms) {
            Ok(()) => {
                self.last_local_instance_publish_ms = Some(now_ms);
            }
            Err(err) => {
                debug!(error = %err, "failed to publish same-host FIPS instance record");
            }
        }
    }

    fn maybe_publish_local_instance_record(&mut self, now_ms: u64) {
        if self.local_instance_registry.is_none() {
            return;
        }
        let interval_ms = self.config.node.discovery.local.publish_interval_ms();
        let due = self
            .last_local_instance_publish_ms
            .map(|last| now_ms.saturating_sub(last) >= interval_ms)
            .unwrap_or(true);
        if due {
            self.publish_local_instance_record(now_ms);
        }
    }

    fn local_instance_scan_due(&self, now_ms: u64) -> bool {
        if self.local_instance_registry.is_none() {
            return false;
        }
        let cfg = &self.config.node.discovery.local;
        let interval_ms = if self
            .local_instance_started_at_ms
            .map(|started| now_ms.saturating_sub(started) <= cfg.startup_scan_duration_ms())
            .unwrap_or(false)
        {
            cfg.startup_scan_interval_ms()
        } else {
            cfg.scan_interval_ms()
        };
        self.last_local_instance_scan_ms
            .map(|last| now_ms.saturating_sub(last) >= interval_ms)
            .unwrap_or(true)
    }

    fn local_instance_peer_allowed(&self, identity: &PeerIdentity) -> bool {
        if self.config.peers().iter().any(|peer| {
            PeerIdentity::from_npub(&peer.npub)
                .map(|configured| configured.node_addr() == identity.node_addr())
                .unwrap_or(false)
        }) {
            return true;
        }
        self.config.node.discovery.nostr.policy == NostrDiscoveryPolicy::Open
    }

    fn local_instance_peer_addresses(
        &self,
        record: &crate::discovery::local::LocalInstanceRecord,
    ) -> Vec<PeerAddress> {
        let mut addresses = Vec::new();
        for contact in &record.contacts {
            if contact.transport != "udp" && contact.transport != "tcp" {
                continue;
            }
            let Ok(socket_addr) = contact.addr.parse::<SocketAddr>() else {
                debug!(
                    npub = %record.npub,
                    transport = %contact.transport,
                    addr = %contact.addr,
                    "local instance discovery: skip non-socket contact"
                );
                continue;
            };
            if !socket_addr.ip().is_loopback() {
                debug!(
                    npub = %record.npub,
                    addr = %contact.addr,
                    "local instance discovery: skip non-loopback contact"
                );
                continue;
            }
            let address =
                PeerAddress::with_priority(contact.transport.clone(), contact.addr.clone(), 10)
                    .with_seen_at_ms(record.updated_at_ms);
            if addresses.iter().any(|existing: &PeerAddress| {
                existing.transport == address.transport && existing.addr == address.addr
            }) {
                continue;
            }
            addresses.push(address);
        }
        addresses
    }

    /// Scan the same-host registry only on startup and then at a low cadence.
    /// This avoids a per-second filesystem poll while preserving the fast path
    /// for processes launched around the same time.
    pub(super) async fn poll_local_instance_discovery(&mut self) {
        let Some(registry) = self.local_instance_registry.clone() else {
            return;
        };
        let now_ms = Self::now_ms();
        self.maybe_publish_local_instance_record(now_ms);
        if !self.local_instance_scan_due(now_ms) {
            return;
        }
        self.last_local_instance_scan_ms = Some(now_ms);

        let records = match registry.scan(now_ms, self.config.node.discovery.local.stale_after_ms())
        {
            Ok(records) => records,
            Err(err) => {
                debug!(error = %err, "same-host FIPS instance scan failed");
                return;
            }
        };
        if records.is_empty() {
            return;
        }

        let mut connect_budget = self.discovery_connect_budget();
        let mut skipped_budget = 0usize;
        for record in records {
            let identity = match PeerIdentity::from_npub(&record.npub) {
                Ok(identity) => identity,
                Err(err) => {
                    debug!(npub = %record.npub, error = %err, "local instance discovery: skip bad npub");
                    continue;
                }
            };
            let peer_node_addr = *identity.node_addr();
            if peer_node_addr == *self.identity.node_addr() {
                continue;
            }
            if !self.local_instance_peer_allowed(&identity) {
                debug!(
                    npub = %identity.short_npub(),
                    "local instance discovery: skip unconfigured peer"
                );
                continue;
            }

            let addresses = self.local_instance_peer_addresses(&record);
            if addresses.is_empty() {
                continue;
            }

            if self.peers.contains_key(&peer_node_addr)
                && self.active_peer_candidate_is_fresh_enough_to_skip(&peer_node_addr, &addresses)
            {
                continue;
            }

            for address in addresses {
                let Some((transport_id, remote_addr)) =
                    self.resolve_peer_address_for_match(&address)
                else {
                    continue;
                };
                if self.is_connecting_to_peer_on_path(&peer_node_addr, transport_id, &remote_addr) {
                    continue;
                }
                if connect_budget == 0 || self.path_candidate_attempt_budget(&peer_node_addr) == 0 {
                    skipped_budget = skipped_budget.saturating_add(1);
                    continue;
                }
                info!(
                    npub = %identity.short_npub(),
                    transport = %address.transport,
                    addr = %address.addr,
                    "same-host FIPS instance discovery: initiating handshake"
                );
                if let Err(err) = self
                    .initiate_connection(transport_id, remote_addr, identity)
                    .await
                {
                    debug!(
                        npub = %record.npub,
                        error = %err,
                        "same-host FIPS instance discovery: failed to initiate connection"
                    );
                }
                connect_budget = connect_budget.saturating_sub(1);
            }
        }
        if skipped_budget > 0 {
            debug!(
                skipped = skipped_budget,
                "same-host FIPS instance discovery connect budget exhausted"
            );
        }
    }

    /// Drain mDNS-discovered peers and initiate Noise XX handshakes. For
    /// active peers this is a non-disruptive alternate-path refresh: the
    /// current link stays live until a new handshake authenticates and
    /// promotes. The handshake itself is the authentication — a spoofed
    /// mDNS advert with someone else's npub fails the XX exchange and
    /// is dropped.
    pub(super) async fn poll_lan_discovery(&mut self) {
        let Some(runtime) = self.lan_discovery.clone() else {
            return;
        };
        let events = runtime.drain_events().await;
        if events.is_empty() {
            return;
        }
        let mut connect_budget = self.discovery_connect_budget();
        let mut skipped_budget = 0usize;
        for event in events {
            let crate::discovery::lan::LanEvent::Discovered(peer) = event;
            let Some((transport_id, local_addr)) =
                self.find_udp_transport_for_remote_addr(peer.addr)
            else {
                debug!(
                    addr = %peer.addr,
                    "lan: skip discovered peer with no compatible UDP transport"
                );
                continue;
            };
            let identity = match crate::PeerIdentity::from_npub(&peer.npub) {
                Ok(id) => id,
                Err(err) => {
                    debug!(npub = %peer.npub, error = %err, "lan: skip bad npub");
                    continue;
                }
            };
            let peer_node_addr = *identity.node_addr();
            let remote_addr = crate::transport::TransportAddr::from_string(&peer.addr.to_string());
            if self.peers.contains_key(&peer_node_addr) {
                let candidate = PeerAddress::new("udp", peer.addr.to_string());
                if self.active_peer_candidate_is_fresh_enough_to_skip(
                    &peer_node_addr,
                    std::slice::from_ref(&candidate),
                ) {
                    continue;
                }
                if self.is_connecting_to_peer_on_path(&peer_node_addr, transport_id, &remote_addr) {
                    continue;
                }
                if connect_budget == 0 || self.path_candidate_attempt_budget(&peer_node_addr) == 0 {
                    skipped_budget = skipped_budget.saturating_add(1);
                    continue;
                }
                info!(
                    npub = %identity.short_npub(),
                    addr = %peer.addr,
                    local_addr = %local_addr,
                    "lan: initiating alternate-path handshake to active peer"
                );
                if let Err(err) = self
                    .initiate_connection(transport_id, remote_addr, identity)
                    .await
                {
                    debug!(
                        npub = %peer.npub,
                        error = %err,
                        "lan: failed to initiate active peer alternate-path handshake"
                    );
                }
                connect_budget = connect_budget.saturating_sub(1);
                continue;
            }
            if self.is_connecting_to_peer_on_path(&peer_node_addr, transport_id, &remote_addr) {
                continue;
            }
            if connect_budget == 0 || self.path_candidate_attempt_budget(&peer_node_addr) == 0 {
                skipped_budget = skipped_budget.saturating_add(1);
                continue;
            }
            info!(
                npub = %identity.short_npub(),
                addr = %peer.addr,
                local_addr = %local_addr,
                "lan: initiating handshake to discovered peer"
            );
            if let Err(err) = self
                .initiate_connection(transport_id, remote_addr, identity)
                .await
            {
                debug!(
                    npub = %peer.npub,
                    error = %err,
                    "lan: failed to initiate connection to discovered peer"
                );
            }
            connect_budget = connect_budget.saturating_sub(1);
        }
        if skipped_budget > 0 {
            debug!(
                skipped = skipped_budget,
                "lan: discovery connect budget exhausted"
            );
        }
    }

    /// Poll pending transport connects and initiate handshakes for ready ones.
    ///
    /// Called from the tick handler. For each pending connect, queries the
    /// transport's connection state. When a connection is established,
    /// marks the link as Connected and starts the Noise handshake.
    /// Failed connections are cleaned up and scheduled for retry.
    pub(super) async fn poll_pending_connects(&mut self) {
        if self.pending_connects.is_empty() {
            return;
        }

        let mut completed = Vec::new();

        for (i, pending) in self.pending_connects.iter().enumerate() {
            let state = if let Some(transport) = self.transports.get(&pending.transport_id) {
                transport.connection_state(&pending.remote_addr)
            } else {
                crate::transport::ConnectionState::Failed("transport removed".into())
            };

            match state {
                crate::transport::ConnectionState::Connected => {
                    completed.push((i, true, None));
                }
                crate::transport::ConnectionState::Failed(reason) => {
                    completed.push((i, false, Some(reason)));
                }
                crate::transport::ConnectionState::Connecting => {
                    // Still in progress, check on next tick
                }
                crate::transport::ConnectionState::None => {
                    // Shouldn't happen — treat as failure
                    completed.push((i, false, Some("no connection attempt found".into())));
                }
            }
        }

        // Process completions in reverse order to preserve indices
        for (i, success, reason) in completed.into_iter().rev() {
            let pending = self.pending_connects.remove(i);

            if success {
                // Mark link as Connected
                if let Some(link) = self.links.get_mut(&pending.link_id) {
                    link.set_connected();
                }

                debug!(
                    peer = %self.peer_display_name(pending.peer_identity.node_addr()),
                    transport_id = %pending.transport_id,
                    remote_addr = %pending.remote_addr,
                    link_id = %pending.link_id,
                    "Transport connected, starting handshake"
                );

                // Start the handshake now that the transport is connected
                if let Err(e) = self
                    .start_handshake(
                        pending.link_id,
                        pending.transport_id,
                        pending.remote_addr.clone(),
                        pending.peer_identity,
                    )
                    .await
                {
                    warn!(
                        link_id = %pending.link_id,
                        error = %e,
                        "Failed to start handshake after transport connect"
                    );
                    // Clean up link on handshake failure
                    self.remove_link(&pending.link_id);
                }
            } else {
                let reason = reason.unwrap_or_default();
                warn!(
                    peer = %self.peer_display_name(pending.peer_identity.node_addr()),
                    transport_id = %pending.transport_id,
                    remote_addr = %pending.remote_addr,
                    link_id = %pending.link_id,
                    reason = %reason,
                    "Transport connect failed"
                );

                // Clean up link and schedule retry
                self.remove_link(&pending.link_id);
                self.links.remove(&pending.link_id);
                self.schedule_retry(*pending.peer_identity.node_addr(), Self::now_ms());
            }
        }
    }

    // === State Transitions ===

    /// Start the node.
    ///
    /// Initializes the TUN interface (if configured), spawns I/O threads,
    /// and transitions to the Running state.
    pub async fn start(&mut self) -> Result<(), NodeError> {
        node_start_debug_log("Node::start begin");
        if !self.state.can_start() {
            return Err(NodeError::AlreadyStarted);
        }
        self.state = NodeState::Starting;
        node_start_debug_log("Node::start state set to starting");

        // Create packet channel for transport -> Node communication
        let packet_buffer_size = self.config.node.buffers.packet_channel;
        let (packet_tx, packet_rx) = packet_channel(packet_buffer_size);
        self.packet_tx = Some(packet_tx.clone());
        self.packet_rx = Some(packet_rx);
        node_start_debug_log("Node::start packet channel created");

        // Initialize transports first (before TUN, before Nostr discovery).
        node_start_debug_log("Node::start create transports begin");
        let transport_handles = self.create_transports(&packet_tx).await;
        node_start_debug_log(format!(
            "Node::start create transports complete count={}",
            transport_handles.len()
        ));

        for mut handle in transport_handles {
            let transport_id = handle.transport_id();
            let transport_type = handle.transport_type().name;
            let name = handle.name().map(|s| s.to_string());

            node_start_debug_log(format!(
                "Node::start transport start begin id={} type={} name={:?}",
                transport_id, transport_type, name
            ));
            match handle.start().await {
                Ok(()) => {
                    node_start_debug_log(format!(
                        "Node::start transport start ok id={} type={}",
                        transport_id, transport_type
                    ));
                    self.transports.insert(transport_id, handle);
                }
                Err(e) => {
                    node_start_debug_log(format!(
                        "Node::start transport start error id={} type={} error={}",
                        transport_id, transport_type, e
                    ));
                    if let Some(ref n) = name {
                        warn!(transport_type, name = %n, error = %e, "Transport failed to start");
                    } else {
                        warn!(transport_type, error = %e, "Transport failed to start");
                    }
                }
            }
        }

        if !self.transports.is_empty() {
            info!(count = self.transports.len(), "Transports initialized");
        }

        // Spawn the off-task FMP-encrypt + UDP-send + FMP-decrypt
        // worker pools. **Unix only** — both pools issue direct
        // sendmmsg(2) / sendmsg(2)+UDP_GSO / recvmmsg(2) calls on
        // raw file descriptors via `AsRawFd`, which is a unix-only
        // trait. On Windows the rx_loop's tokio-based send/recv
        // remain the canonical path; the perf overhaul lands its
        // gains on unix.
        //
        // Worker count defaults to the number of CPUs, overridable
        // via `FIPS_ENCRYPT_WORKERS=N` / `FIPS_DECRYPT_WORKERS=N`
        // for debug / benchmarking. Hash-by-destination means a
        // single TCP flow pins to one worker (preserves wire
        // ordering); additional workers light up under multi-flow
        // / multi-peer load. See `node::encrypt_worker` /
        // `node::decrypt_worker` for full rationale.
        #[cfg(unix)]
        {
            if self.config.node.worker_pools_enabled {
                node_start_debug_log("Node::start worker pools begin");
                let cpu_default = std::thread::available_parallelism()
                    .map(|n| n.get())
                    .unwrap_or(1)
                    .max(1);
                let encrypt_worker_count: usize = std::env::var("FIPS_ENCRYPT_WORKERS")
                    .ok()
                    .and_then(|s| s.parse().ok())
                    .unwrap_or(cpu_default)
                    .max(1);
                self.encrypt_workers = Some(super::encrypt_worker::EncryptWorkerPool::spawn(
                    encrypt_worker_count,
                ));
                info!(
                    workers = encrypt_worker_count,
                    "Spawned FMP-encrypt worker pool"
                );

                // `FIPS_DECRYPT_WORKERS=0` disables the pool entirely and
                // falls through to the in-line rx_loop decrypt path (the
                // "test-mode" branch in `handle_encrypted_frame`, which is
                // in fact a fully functional synchronous decrypt). Useful
                // as an A/B against the worker pipeline when chasing
                // scheduling/queueing regressions on the native macOS
                // path. Any non-zero value (env or default) spawns the
                // pool as before.
                let decrypt_worker_count: usize = std::env::var("FIPS_DECRYPT_WORKERS")
                    .ok()
                    .and_then(|s| s.parse().ok())
                    .unwrap_or(cpu_default);
                if decrypt_worker_count == 0 {
                    info!("FIPS_DECRYPT_WORKERS=0 → in-line decrypt in rx_loop (no worker pool)");
                } else {
                    self.decrypt_workers = Some(super::decrypt_worker::DecryptWorkerPool::spawn(
                        decrypt_worker_count,
                    ));
                    info!(
                        workers = decrypt_worker_count,
                        "Spawned FMP+FSP-decrypt worker pool"
                    );
                }
                node_start_debug_log("Node::start worker pools complete");
            } else {
                node_start_debug_log("Node::start worker pools disabled");
                info!("FIPS worker pools disabled; using in-line crypto/send path");
            }
        }

        if self.config.node.discovery.nostr.enabled {
            node_start_debug_log("Node::start nostr discovery start begin");
            match NostrDiscovery::start(&self.identity, self.config.node.discovery.nostr.clone())
                .await
            {
                Ok(runtime) => {
                    node_start_debug_log("Node::start nostr discovery runtime created");
                    if let Err(err) = self.refresh_overlay_advert(&runtime).await {
                        warn!(error = %err, "Failed to publish initial Nostr overlay advert");
                    }
                    node_start_debug_log("Node::start nostr overlay advert refreshed");
                    self.nostr_discovery = Some(runtime);
                    self.nostr_discovery_started_at_ms = Some(Self::now_ms());
                    info!("Nostr overlay discovery enabled");
                }
                Err(err) => {
                    node_start_debug_log(format!(
                        "Node::start nostr discovery start error error={}",
                        err
                    ));
                    warn!(error = %err, "Failed to start Nostr overlay discovery");
                }
            }
        }

        // mDNS / DNS-SD LAN discovery. Independent of Nostr — runs even
        // when Nostr is disabled, since it gives us sub-second pairing
        // on the same link without any relay or NAT-traversal roundtrip.
        if self.config.node.discovery.lan.enabled {
            node_start_debug_log("Node::start lan discovery start begin");
            let advertised_udp_port = self
                .transports
                .values()
                .filter(|h| h.is_operational())
                .filter(|h| h.transport_type().name == "udp")
                .find_map(|h| h.local_addr().map(|addr| addr.port()))
                .unwrap_or(0);
            let scope = self.lan_discovery_scope();
            match crate::discovery::lan::LanDiscovery::start(
                &self.identity,
                scope,
                advertised_udp_port,
                self.config.node.discovery.lan.clone(),
            )
            .await
            {
                Ok(runtime) => {
                    node_start_debug_log("Node::start lan discovery start ok");
                    self.lan_discovery = Some(runtime);
                    info!("LAN mDNS discovery enabled");
                }
                Err(err) => {
                    node_start_debug_log(format!(
                        "Node::start lan discovery start error error={}",
                        err
                    ));
                    debug!(error = %err, "LAN mDNS discovery not started");
                }
            }
        }

        self.start_local_instance_discovery();
        self.poll_local_instance_discovery().await;

        // Connect to static peers before TUN is active
        // This allows handshake messages to be sent before we start accepting packets
        node_start_debug_log("Node::start initiate peer connections begin");
        self.initiate_peer_connections().await;
        node_start_debug_log("Node::start initiate peer connections complete");

        // Initialize TUN interface last, after transports and peers are ready
        if self.config.tun.enabled {
            node_start_debug_log("Node::start tun init begin");
            let address = *self.identity.address();
            match TunDevice::create(&self.config.tun, address).await {
                Ok(device) => {
                    let mtu = device.mtu();
                    let name = device.name().to_string();
                    let our_addr = *device.address();

                    info!("TUN device active:");
                    info!("     name: {}", name);
                    info!("  address: {}", device.address());
                    info!("      mtu: {}", mtu);

                    // Calculate max MSS for TCP clamping
                    let effective_mtu = self.effective_ipv6_mtu();
                    let max_mss = effective_mtu.saturating_sub(40).saturating_sub(20); // IPv6 + TCP headers

                    info!("effective MTU: {} bytes", effective_mtu);
                    debug!("   max TCP MSS: {} bytes", max_mss);

                    // On macOS, create a shutdown pipe. Writing to it unblocks the
                    // reader thread's select() loop without closing the TUN fd
                    // (which would cause a double-close when TunDevice drops).
                    #[cfg(target_os = "macos")]
                    let (shutdown_read_fd, shutdown_write_fd) = {
                        let mut fds = [0i32; 2];
                        if unsafe { libc::pipe(fds.as_mut_ptr()) } < 0 {
                            return Err(NodeError::Tun(crate::upper::tun::TunError::Configure(
                                "failed to create shutdown pipe".into(),
                            )));
                        }
                        (fds[0], fds[1])
                    };

                    // Create writer (dups the fd for independent write access).
                    // Pass path_mtu_lookup so inbound SYN-ACK clamp can read
                    // per-destination path MTU learned via discovery.
                    let (writer, tun_tx) =
                        device.create_writer(max_mss, self.path_mtu_lookup.clone())?;

                    // Spawn writer thread
                    let writer_handle = thread::spawn(move || {
                        writer.run();
                    });

                    // Clone tun_tx for the reader
                    let reader_tun_tx = tun_tx.clone();

                    // Create outbound channel for TUN reader → Node
                    let tun_channel_size = self.config.node.buffers.tun_channel;
                    let (outbound_tx, outbound_rx) = tokio::sync::mpsc::channel(tun_channel_size);

                    // Spawn reader thread
                    let transport_mtu = self.transport_mtu();
                    let path_mtu_lookup = self.path_mtu_lookup.clone();
                    #[cfg(target_os = "macos")]
                    let reader_handle = thread::spawn(move || {
                        run_tun_reader(
                            device,
                            mtu,
                            our_addr,
                            reader_tun_tx,
                            outbound_tx,
                            transport_mtu,
                            path_mtu_lookup,
                            shutdown_read_fd,
                        );
                    });
                    #[cfg(not(target_os = "macos"))]
                    let reader_handle = thread::spawn(move || {
                        run_tun_reader(
                            device,
                            mtu,
                            our_addr,
                            reader_tun_tx,
                            outbound_tx,
                            transport_mtu,
                            path_mtu_lookup,
                        );
                    });

                    self.tun_state = TunState::Active;
                    self.tun_name = Some(name);
                    self.tun_tx = Some(tun_tx);
                    self.tun_outbound_rx = Some(outbound_rx);
                    self.tun_reader_handle = Some(reader_handle);
                    self.tun_writer_handle = Some(writer_handle);
                    #[cfg(target_os = "macos")]
                    {
                        self.tun_shutdown_fd = Some(shutdown_write_fd);
                    }
                }
                Err(e) => {
                    self.tun_state = TunState::Failed;
                    warn!(error = %e, "Failed to initialize TUN, continuing without it");
                }
            }
            node_start_debug_log("Node::start tun init complete");
        }

        // Initialize DNS responder (independent of TUN).
        //
        // Default bind_addr is "::1" (IPv6 loopback). The shipped
        // fips-dns-setup configures systemd-resolved via a global
        // /etc/systemd/resolved.conf.d/fips.conf drop-in pointing at
        // [::1]:5354, which sidesteps a Linux IPV6_PKTINFO behaviour
        // where self-destined traffic to fips0's address is attributed
        // to fips0 in PKTINFO and gets silently dropped by the
        // mesh-interface filter in src/upper/dns.rs.
        //
        // For mesh-reachable resolution (rare), set bind_addr: "::"
        // in fips.yaml. The mesh-interface filter remains active to
        // prevent hosts-file alias enumeration in that mode.
        // `IPV6_V6ONLY=0` is set explicitly so IPv4 clients on
        // 127.0.0.1 still reach us regardless of kernel sysctl
        // defaults — but only when bind is on a wildcard / IPv6 path.
        if self.config.dns.enabled {
            node_start_debug_log("Node::start dns init begin");
            let addr_str = self.config.dns.bind_addr();
            match addr_str.parse::<std::net::IpAddr>() {
                Ok(ip) => {
                    let bind = std::net::SocketAddr::new(ip, self.config.dns.port());
                    match Self::bind_dns_socket(bind) {
                        Ok(socket) => {
                            let dns_channel_size = self.config.node.buffers.dns_channel;
                            let (identity_tx, identity_rx) =
                                tokio::sync::mpsc::channel(dns_channel_size);
                            let dns_ttl = self.config.dns.ttl();
                            let base_hosts = crate::upper::hosts::HostMap::from_peer_configs(
                                self.config.peers(),
                            );
                            let reloader = if self.config.node.system_files_enabled {
                                let hosts_path = std::path::PathBuf::from(
                                    crate::upper::hosts::DEFAULT_HOSTS_PATH,
                                );
                                crate::upper::hosts::HostMapReloader::new(base_hosts, hosts_path)
                            } else {
                                crate::upper::hosts::HostMapReloader::memory_only(base_hosts)
                            };
                            // Resolve the TUN ifindex so the responder can
                            // drop queries arriving on the mesh interface
                            // (fips0). Without this, the `::` bind exposes
                            // /etc/fips/hosts alias probing to any mesh peer.
                            // When TUN isn't enabled or the name can't be
                            // resolved, `None` disables the filter (there
                            // is no mesh surface to defend anyway).
                            let mesh_ifindex = Self::lookup_mesh_ifindex(self.config.tun.name());
                            info!(
                                bind = %bind,
                                hosts = reloader.hosts().len(),
                                mesh_ifindex = ?mesh_ifindex,
                                "DNS responder started for .fips domain (auto-reload enabled)"
                            );
                            let handle = tokio::spawn(crate::upper::dns::run_dns_responder(
                                socket,
                                identity_tx,
                                dns_ttl,
                                reloader,
                                mesh_ifindex,
                            ));
                            self.dns_identity_rx = Some(identity_rx);
                            self.dns_task = Some(handle);
                        }
                        Err(e) => {
                            warn!(bind = %bind, error = %e, "Failed to start DNS responder");
                        }
                    }
                }
                Err(e) => {
                    warn!(addr = %addr_str, error = %e, "Invalid dns.bind_addr; DNS responder not started");
                }
            }
            node_start_debug_log("Node::start dns init complete");
        }

        self.state = NodeState::Running;
        node_start_debug_log("Node::start running");
        info!("Node started:");
        info!("       state: {}", self.state);
        info!("  transports: {}", self.transports.len());
        info!(" connections: {}", self.connections.len());
        Ok(())
    }

    /// Bind a UDP socket for the DNS responder.
    ///
    /// For IPv6 binds (including `::`), sets `IPV6_V6ONLY=0` so the socket
    /// also accepts IPv4-mapped addresses. This guarantees dual-stack
    /// delivery regardless of `net.ipv6.bindv6only` sysctl on the host —
    /// v4 clients on 127.0.0.1 and v6 clients on the fips0 address both
    /// land on the same socket.
    ///
    /// Also enables `IPV6_RECVPKTINFO` on IPv6 sockets so the responder
    /// can learn the arrival interface per packet. The responder uses that
    /// to drop queries arriving on the mesh TUN, closing the hosts-file
    /// probing side-channel created by the `::` bind.
    fn bind_dns_socket(
        addr: std::net::SocketAddr,
    ) -> Result<tokio::net::UdpSocket, std::io::Error> {
        use socket2::{Domain, Protocol, Socket, Type};
        let domain = if addr.is_ipv4() {
            Domain::IPV4
        } else {
            Domain::IPV6
        };
        let sock = Socket::new(domain, Type::DGRAM, Some(Protocol::UDP))?;
        if addr.is_ipv6() {
            sock.set_only_v6(false)?;
            #[cfg(unix)]
            Self::set_recv_pktinfo_v6(&sock)?;
        }
        sock.set_nonblocking(true)?;
        sock.bind(&addr.into())?;
        tokio::net::UdpSocket::from_std(sock.into())
    }

    /// Enable `IPV6_RECVPKTINFO` on an IPv6 UDP socket.
    ///
    /// After this setsockopt, each `recvmsg()` call on the socket receives
    /// an `IPV6_PKTINFO` control message containing the arrival interface
    /// index, which the DNS responder uses for its mesh-interface filter.
    #[cfg(unix)]
    fn set_recv_pktinfo_v6(sock: &socket2::Socket) -> Result<(), std::io::Error> {
        use std::os::fd::AsRawFd;
        let enable: libc::c_int = 1;
        let ret = unsafe {
            libc::setsockopt(
                sock.as_raw_fd(),
                libc::IPPROTO_IPV6,
                libc::IPV6_RECVPKTINFO,
                &enable as *const _ as *const libc::c_void,
                std::mem::size_of::<libc::c_int>() as libc::socklen_t,
            )
        };
        if ret < 0 {
            return Err(std::io::Error::last_os_error());
        }
        Ok(())
    }

    /// Resolve the mesh TUN interface index by name.
    ///
    /// Returns `None` if the interface does not exist (e.g. TUN disabled
    /// or not yet created). A `None` result disables the DNS responder's
    /// mesh-interface filter — safe, because if there is no fips0 there
    /// is no mesh exposure to defend against.
    fn lookup_mesh_ifindex(name: &str) -> Option<u32> {
        #[cfg(unix)]
        {
            let c_name = std::ffi::CString::new(name).ok()?;
            let idx = unsafe { libc::if_nametoindex(c_name.as_ptr()) };
            if idx == 0 { None } else { Some(idx) }
        }
        #[cfg(not(unix))]
        {
            let _ = name;
            None
        }
    }

    /// Stop the node.
    ///
    /// Shuts down TUN interface, stops I/O threads, and transitions to
    /// the Stopped state.
    pub async fn stop(&mut self) -> Result<(), NodeError> {
        if !self.state.can_stop() {
            return Err(NodeError::NotStarted);
        }
        self.state = NodeState::Stopping;
        info!(state = %self.state, "Node stopping");

        // Stop DNS responder
        if let Some(handle) = self.dns_task.take() {
            handle.abort();
            debug!("DNS responder stopped");
        }

        // Send disconnect notifications to all active peers before closing transports
        self.send_disconnect_to_all_peers(DisconnectReason::Shutdown)
            .await;

        // Stop Nostr overlay discovery background work and withdraw any advert.
        if let Some(bootstrap) = self.nostr_discovery.take()
            && let Err(e) = bootstrap.shutdown().await
        {
            warn!(error = %e, "Failed to shutdown Nostr overlay discovery");
        }

        // Tear down LAN mDNS responder + browser. Best-effort: the
        // OS will eventually time the advert out via its TTL even if
        // we don't get a clean unregister out before the daemon exits.
        if let Some(lan) = self.lan_discovery.take() {
            lan.shutdown().await;
        }

        if let Some(registry) = self.local_instance_registry.take()
            && let Err(err) = registry.remove()
        {
            debug!(error = %err, "failed to remove same-host FIPS instance record");
        }

        // Shutdown transports (they're packet producers)
        let transport_ids: Vec<_> = self.transports.keys().cloned().collect();
        for transport_id in transport_ids {
            if let Some(mut handle) = self.transports.remove(&transport_id) {
                let transport_type = handle.transport_type().name;
                match handle.stop().await {
                    Ok(()) => {
                        info!(transport_id = %transport_id, transport_type, "Transport stopped");
                    }
                    Err(e) => {
                        warn!(
                            transport_id = %transport_id,
                            transport_type,
                            error = %e,
                            "Transport stop failed"
                        );
                    }
                }
            }
        }

        // Drop packet channels
        self.packet_tx.take();
        self.packet_rx.take();

        // Shutdown TUN interface
        if let Some(name) = self.tun_name.take() {
            info!(name = %name, "Shutting down TUN interface");

            // Drop the tun_tx to signal the writer to stop
            self.tun_tx.take();

            // Delete the interface (on Linux, causes reader to get EFAULT)
            if let Err(e) = shutdown_tun_interface(&name).await {
                warn!(name = %name, error = %e, "Failed to shutdown TUN interface");
            }

            // On macOS, signal the reader thread to exit by writing to the
            // shutdown pipe. The reader's select() will wake up and break.
            #[cfg(target_os = "macos")]
            if let Some(fd) = self.tun_shutdown_fd.take() {
                unsafe {
                    libc::write(fd, b"x".as_ptr() as *const libc::c_void, 1);
                    libc::close(fd);
                }
            }

            // Wait for threads to finish
            if let Some(handle) = self.tun_reader_handle.take() {
                let _ = handle.join();
            }
            if let Some(handle) = self.tun_writer_handle.take() {
                let _ = handle.join();
            }

            self.tun_state = TunState::Disabled;
        }

        self.state = NodeState::Stopped;
        info!(state = %self.state, "Node stopped");
        Ok(())
    }

    /// Send disconnect notifications to all active peers.
    ///
    /// Best-effort: send failures are logged and ignored since the transport
    /// may already be degraded. This runs before transports are shut down.
    async fn send_disconnect_to_all_peers(&mut self, reason: DisconnectReason) {
        let disconnect = Disconnect::new(reason);
        let plaintext = disconnect.encode();

        // Collect node_addrs to avoid borrow conflict with send helper
        let peer_addrs: Vec<NodeAddr> = self
            .peers
            .iter()
            .filter(|(_, peer)| peer.can_send() && peer.has_session())
            .map(|(addr, _)| *addr)
            .collect();

        if peer_addrs.is_empty() {
            debug!(
                total_peers = self.peers.len(),
                "No sendable peers for disconnect notification"
            );
            return;
        }

        let mut sent = 0usize;
        for node_addr in &peer_addrs {
            match self
                .send_encrypted_link_message(node_addr, &plaintext)
                .await
            {
                Ok(()) => sent += 1,
                Err(e) => {
                    debug!(
                        peer = %self.peer_display_name(node_addr),
                        error = %e,
                        "Failed to send disconnect (transport may be down)"
                    );
                }
            }
        }

        info!(sent, total = peer_addrs.len(), reason = %reason, "Sent disconnect notifications");
    }

    pub(in crate::node) fn static_peer_addresses(
        &self,
        peer_config: &PeerConfig,
    ) -> Vec<PeerAddress> {
        peer_config
            .addresses_by_priority()
            .into_iter()
            .cloned()
            .collect()
    }

    async fn nostr_peer_fallback_addresses(
        &self,
        peer_config: &PeerConfig,
        existing: &[PeerAddress],
    ) -> Vec<PeerAddress> {
        if !self.config.node.discovery.nostr.enabled
            || self.config.node.discovery.nostr.policy
                == crate::config::NostrDiscoveryPolicy::Disabled
        {
            return Vec::new();
        }

        let Some(bootstrap) = self.nostr_discovery.clone() else {
            return Vec::new();
        };
        if self.nostr_cooldown_applies_to_peer_config(peer_config)
            && bootstrap
                .cooldown_until(&peer_config.npub, Self::now_ms())
                .is_some()
        {
            debug!(
                npub = %peer_config.npub,
                "Skipping cached Nostr fallback endpoints while peer is in traversal cooldown"
            );
            return Vec::new();
        }
        let endpoints = match bootstrap
            .cached_advert_endpoints_for_peer(&peer_config.npub)
            .await
        {
            Some(endpoints) => endpoints,
            None => {
                debug!(
                    npub = %peer_config.npub,
                    "No cached Nostr advert endpoints for configured peer"
                );
                return Vec::new();
            }
        };

        let mut fallback = Vec::new();
        let mut next_priority = existing
            .iter()
            .map(|addr| addr.priority)
            .max()
            .unwrap_or(100)
            .saturating_add(1);
        // Stamp every overlay-derived candidate with the current wall clock.
        // The dialer still honors explicit priority first; this timestamp is
        // only a recency tiebreaker within the same priority tier. We use a
        // single timestamp per fetch because all candidates in one advert are
        // equally fresh.
        let seen_at_ms = Self::now_ms();
        for endpoint in endpoints {
            let Some(candidate) =
                Self::overlay_endpoint_to_peer_address(&endpoint, next_priority, seen_at_ms)
            else {
                continue;
            };
            if existing
                .iter()
                .any(|addr| addr.transport == candidate.transport && addr.addr == candidate.addr)
                || fallback.iter().any(|addr: &PeerAddress| {
                    addr.transport == candidate.transport && addr.addr == candidate.addr
                })
            {
                continue;
            }
            fallback.push(candidate);
            next_priority = next_priority.saturating_add(1);
        }
        fallback
    }

    pub(in crate::node) async fn request_nostr_bootstrap(&self, peer_config: &PeerConfig) -> bool {
        if !self.config.node.discovery.nostr.enabled
            || self.config.node.discovery.nostr.policy
                == crate::config::NostrDiscoveryPolicy::Disabled
        {
            return false;
        }
        let Some(bootstrap) = self.nostr_discovery.clone() else {
            return false;
        };
        let now_ms = Self::now_ms();
        if self.nostr_cooldown_applies_to_peer_config(peer_config)
            && let Some(cooldown_until_ms) = bootstrap.cooldown_until(&peer_config.npub, now_ms)
        {
            debug!(
                npub = %peer_config.npub,
                cooldown_secs = cooldown_until_ms.saturating_sub(now_ms) / 1000,
                "Skipping Nostr traversal request while peer is in cooldown"
            );
            return false;
        }
        bootstrap.set_outbound_admission(self.open_discovery_outbound_admission_check());
        bootstrap.set_direct_refresh_admission(self.outbound_direct_refresh_admission_check());
        let mesh_signaling_allowed = self.mesh_signaling_allowed_for_peer(peer_config);
        let started = bootstrap
            .request_connect_with_mesh_signaling(peer_config.clone(), mesh_signaling_allowed)
            .await;
        if started {
            info!(
                npub = %peer_config.npub,
                mesh_signaling_allowed,
                "Started background UDP NAT traversal attempt"
            );
        } else {
            debug!(
                npub = %peer_config.npub,
                mesh_signaling_allowed,
                "Background UDP NAT traversal attempt already in progress"
            );
        }
        true
    }

    fn nostr_cooldown_applies_to_peer_config(&self, peer_config: &PeerConfig) -> bool {
        !self.mesh_signaling_allowed_for_peer(peer_config)
    }

    pub(in crate::node) fn mesh_signaling_allowed_for_peer(
        &self,
        peer_config: &PeerConfig,
    ) -> bool {
        let Ok(identity) = PeerIdentity::from_npub(&peer_config.npub) else {
            return false;
        };
        let peer_addr = identity.node_addr();
        self.configured_peer(peer_addr).is_some()
    }

    fn overlay_endpoint_to_peer_address(
        endpoint: &OverlayEndpointAdvert,
        priority: u8,
        seen_at_ms: u64,
    ) -> Option<PeerAddress> {
        let transport = match endpoint.transport {
            OverlayTransportKind::Udp => "udp",
            OverlayTransportKind::Tcp => "tcp",
            OverlayTransportKind::Tor => "tor",
            OverlayTransportKind::WebRtc => "webrtc",
        };
        Some(
            PeerAddress::with_priority(transport, endpoint.addr.clone(), priority)
                .with_seen_at_ms(seen_at_ms),
        )
    }

    async fn attempt_peer_address_list(
        &mut self,
        peer_config: &PeerConfig,
        peer_identity: PeerIdentity,
        allow_bootstrap_nat: bool,
        addresses: &[PeerAddress],
    ) -> Result<(), NodeError> {
        let mut attempted = false;
        let mut local_route_error = None;
        let peer_node_addr = *peer_identity.node_addr();
        let mut concrete_budget = self.path_candidate_attempt_budget(&peer_node_addr);

        for addr in addresses {
            if addr.transport == "udp" && addr.addr.eq_ignore_ascii_case("nat") {
                if !allow_bootstrap_nat {
                    continue;
                }
                if self.request_nostr_bootstrap(peer_config).await {
                    attempted = true;
                    continue;
                }
                debug!(npub = %peer_config.npub, "No Nostr overlay runtime for udp:nat address");
                continue;
            }

            let (transport_id, remote_addr) = if addr.transport == "ethernet" {
                match self.resolve_ethernet_addr(&addr.addr) {
                    Ok(result) => result,
                    Err(e) => {
                        debug!(
                            transport = %addr.transport,
                            addr = %addr.addr,
                            error = %e,
                            "Failed to resolve Ethernet address"
                        );
                        continue;
                    }
                }
            } else if addr.transport == "ble" {
                #[cfg(bluer_available)]
                {
                    match self.resolve_ble_addr(&addr.addr) {
                        Ok(result) => result,
                        Err(e) => {
                            debug!(
                                transport = %addr.transport,
                                addr = %addr.addr,
                                error = %e,
                                "Failed to resolve BLE address"
                            );
                            continue;
                        }
                    }
                }
                #[cfg(not(bluer_available))]
                {
                    debug!(transport = %addr.transport, "BLE transport not available on this build");
                    continue;
                }
            } else {
                let tid = if addr.transport == "udp"
                    && let Ok(remote_socket_addr) = addr.addr.parse::<SocketAddr>()
                {
                    match self.find_udp_transport_for_remote_addr(remote_socket_addr) {
                        Some((id, _)) => id,
                        None => {
                            debug!(
                                transport = %addr.transport,
                                addr = %addr.addr,
                                "No compatible operational UDP transport for address"
                            );
                            continue;
                        }
                    }
                } else {
                    match self.find_transport_for_type(&addr.transport) {
                        Some(id) => id,
                        None => {
                            debug!(
                                transport = %addr.transport,
                                addr = %addr.addr,
                                "No operational transport for address type"
                            );
                            continue;
                        }
                    }
                };
                (tid, TransportAddr::from_string(&addr.addr))
            };

            if self.is_connecting_to_peer_on_path(&peer_node_addr, transport_id, &remote_addr) {
                attempted = true;
                debug!(
                    npub = %peer_config.npub,
                    transport_id = %transport_id,
                    remote_addr = %remote_addr,
                    "Skipping duplicate in-flight candidate path"
                );
                continue;
            }

            if concrete_budget == 0
                && self.reclaim_lower_priority_inflight_candidate_for_peer(&peer_node_addr, addr)
            {
                concrete_budget = self.path_candidate_attempt_budget(&peer_node_addr);
            }

            if concrete_budget == 0 {
                debug!(
                    npub = %peer_config.npub,
                    max_candidates = MAX_PARALLEL_PATH_CANDIDATES_PER_PEER,
                    "Path candidate race budget exhausted"
                );
                break;
            }

            match self
                .initiate_connection(transport_id, remote_addr, peer_identity)
                .await
            {
                Ok(()) => {
                    attempted = true;
                    concrete_budget = concrete_budget.saturating_sub(1);
                }
                Err(e @ NodeError::AccessDenied(_)) => return Err(e),
                Err(e) => {
                    if e.is_local_route_unavailable() && local_route_error.is_none() {
                        local_route_error = Some(e.to_string());
                    }
                    debug!(
                        npub = %peer_config.npub,
                        transport_id = %transport_id,
                        error = %e,
                        "Connection attempt failed, trying next address"
                    );
                }
            }
        }

        if attempted {
            return Ok(());
        }

        if let Some(error) = local_route_error {
            return Err(NodeError::LocalRouteUnavailable(error));
        }

        Err(NodeError::NoTransportForType(format!(
            "no operational transport for any of {}'s addresses",
            peer_config.npub
        )))
    }

    async fn queue_open_discovery_retries(&mut self, bootstrap: &std::sync::Arc<NostrDiscovery>) {
        self.run_open_discovery_sweep(bootstrap, None, "per-tick")
            .await;
    }

    pub(in crate::node) fn queue_active_fallback_direct_retries(
        &mut self,
        _bootstrap: &std::sync::Arc<NostrDiscovery>,
    ) {
        let now_ms = Self::now_ms();
        let peer_configs = self
            .config
            .auto_connect_peers()
            .cloned()
            .collect::<Vec<_>>();

        for peer_config in peer_configs {
            let Ok(peer_identity) = PeerIdentity::from_npub(&peer_config.npub) else {
                continue;
            };
            let node_addr = *peer_identity.node_addr();

            if self.retry_pending.contains_key(&node_addr)
                || !self.peers.contains_key(&node_addr)
                || self.is_connecting_to_peer(&node_addr)
                || !self.active_peer_should_keep_direct_retry(&node_addr, &peer_config)
            {
                continue;
            }

            let mut state = super::retry::RetryState::new(peer_config.clone());
            state.reconnect = true;
            state.retry_after_ms = now_ms;
            self.retry_pending.insert(node_addr, state);

            debug!(
                peer = %self.peer_display_name(&node_addr),
                "Queued direct-path retry for active fallback peer"
            );
        }
    }

    /// Open-discovery cache sweep. Iterates the cached overlay adverts and
    /// queues retries for non-configured, not-yet-connected peers.
    ///
    /// `max_age_secs`, if set, filters out adverts whose `created_at` is
    /// older than `now - max_age_secs`. The per-tick sweep passes `None`
    /// (relies on the cache's own `valid_until_ms` filter); the one-shot
    /// startup sweep passes `Some(startup_sweep_max_age_secs)`.
    ///
    /// `caller` is a short label included in log lines so per-tick and
    /// startup sweeps are distinguishable in operator-facing logs.
    pub(in crate::node) async fn run_open_discovery_sweep(
        &mut self,
        bootstrap: &std::sync::Arc<NostrDiscovery>,
        max_age_secs: Option<u64>,
        caller: &'static str,
    ) {
        if !self.config.node.discovery.nostr.enabled
            || self.config.node.discovery.nostr.policy != crate::config::NostrDiscoveryPolicy::Open
        {
            return;
        }

        let configured_npubs = self
            .config
            .peers()
            .iter()
            .map(|peer| peer.npub.clone())
            .collect::<HashSet<_>>();
        let now_ms = Self::now_ms();
        let now_secs = now_ms / 1000;
        let mut enqueue_budget = self.open_discovery_enqueue_budget(&configured_npubs);
        if enqueue_budget == 0 {
            debug!(
                caller = %caller,
                "open-discovery sweep: enqueue budget is 0, skipping"
            );
            return;
        }

        let candidates = bootstrap.cached_open_discovery_candidates(64).await;
        let cached_count = candidates.len();
        let mut enqueued = 0usize;
        let mut skipped_age = 0usize;
        let mut skipped_configured = 0usize;
        let mut skipped_self = 0usize;
        let mut skipped_connected = 0usize;
        let mut skipped_retry_pending = 0usize;
        let mut skipped_connecting = 0usize;
        let mut skipped_no_endpoints = 0usize;
        let mut skipped_invalid_npub = 0usize;
        let mut skipped_cooldown = 0usize;

        for (npub, endpoints, created_at_secs) in candidates {
            if enqueue_budget == 0 {
                break;
            }

            if let Some(max_age) = max_age_secs
                && now_secs.saturating_sub(created_at_secs) > max_age
            {
                skipped_age = skipped_age.saturating_add(1);
                continue;
            }

            if configured_npubs.contains(&npub) {
                // Configured peers don't go through the open-discovery
                // enqueue path — their `PeerConfig` is already in
                // `self.config.peers()`, so the regular retry queue is
                // what drives their reconnect. But on cold start with
                // NAT'd peers, every initial `initiate_peer_connection`
                // fails (no overlay data yet, static cache hints empty
                // or stale), each pushes the peer into `retry_pending`
                // with exponential backoff (5/10/20/40/80s), and by the
                // time the next backoff slot fires the Nostr advert is
                // already cached — we just don't act on it for ~80s.
                //
                // The arrival of an advert (which this sweep sees) means
                // we now have a path to dial. If the peer's retry is
                // scheduled in the future, pull it forward to "now" so
                // the next `process_pending_retries` tick fires it
                // immediately. The retry path (`initiate_peer_retry_
                // connection` → `try_peer_addresses`) then refetches
                // the advert and dials it — no behavioral change
                // beyond schedule timing.
                if let Ok(identity) = PeerIdentity::from_npub(&npub) {
                    let configured_addr = *identity.node_addr();
                    if bootstrap.cooldown_until(&npub, now_ms).is_some() {
                        skipped_cooldown = skipped_cooldown.saturating_add(1);
                        skipped_configured = skipped_configured.saturating_add(1);
                        continue;
                    }
                    if let Some(state) = self.retry_pending.get_mut(&configured_addr)
                        && state.retry_after_ms > now_ms
                    {
                        state.retry_after_ms = now_ms;
                        debug!(
                            caller = %caller,
                            peer = %self.peer_display_name(&configured_addr),
                            advert_age_secs = now_secs.saturating_sub(created_at_secs),
                            "Expediting configured-peer retry after fresh overlay advert"
                        );
                    }
                }
                skipped_configured = skipped_configured.saturating_add(1);
                continue;
            }

            let peer_identity = match PeerIdentity::from_npub(&npub) {
                Ok(identity) => identity,
                Err(_) => {
                    skipped_invalid_npub = skipped_invalid_npub.saturating_add(1);
                    continue;
                }
            };
            let node_addr = *peer_identity.node_addr();
            if node_addr == *self.identity.node_addr() {
                skipped_self = skipped_self.saturating_add(1);
                continue;
            }
            if self.peers.contains_key(&node_addr) {
                skipped_connected = skipped_connected.saturating_add(1);
                continue;
            }
            if self.retry_pending.contains_key(&node_addr) {
                skipped_retry_pending = skipped_retry_pending.saturating_add(1);
                continue;
            }
            if bootstrap.cooldown_until(&npub, now_ms).is_some() {
                skipped_cooldown = skipped_cooldown.saturating_add(1);
                continue;
            }
            let connecting = self.connections.values().any(|conn| {
                conn.expected_identity()
                    .map(|id| id.node_addr() == &node_addr)
                    .unwrap_or(false)
            });
            if connecting {
                skipped_connecting = skipped_connecting.saturating_add(1);
                continue;
            }

            let mut addresses = Vec::new();
            let mut priority = 120u8;
            let seen_at_ms = Self::now_ms();
            for endpoint in endpoints {
                let Some(candidate) =
                    Self::overlay_endpoint_to_peer_address(&endpoint, priority, seen_at_ms)
                else {
                    continue;
                };
                if addresses.iter().any(|existing: &PeerAddress| {
                    existing.transport == candidate.transport && existing.addr == candidate.addr
                }) {
                    continue;
                }
                addresses.push(candidate);
                priority = priority.saturating_add(1);
            }
            if addresses.is_empty() {
                skipped_no_endpoints = skipped_no_endpoints.saturating_add(1);
                continue;
            }

            self.peer_aliases
                .entry(node_addr)
                .or_insert_with(|| peer_identity.short_npub());
            self.register_identity(node_addr, peer_identity.pubkey_full());

            let mut state = super::retry::RetryState::new(PeerConfig {
                npub: npub.clone(),
                alias: None,
                addresses,
                connect_policy: ConnectPolicy::AutoConnect,
                auto_reconnect: true,
                discovery_fallback_transit: false,
            });
            state.reconnect = false;
            state.retry_after_ms = now_ms;
            state.expires_at_ms = Some(self.open_discovery_retry_expires_at_ms(now_ms));
            self.retry_pending.insert(node_addr, state);
            info!(
                caller = %caller,
                peer = %peer_identity.short_npub(),
                advert_age_secs = now_secs.saturating_sub(created_at_secs),
                "open-discovery sweep: queued retry for cached advert"
            );
            enqueue_budget = enqueue_budget.saturating_sub(1);
            enqueued = enqueued.saturating_add(1);
        }

        // Always log a one-line summary on the startup sweep so operators
        // can verify it ran. Per-tick sweeps are noisier; only summarize
        // when something happened.
        let total_skipped = skipped_age
            + skipped_configured
            + skipped_self
            + skipped_connected
            + skipped_retry_pending
            + skipped_connecting
            + skipped_no_endpoints
            + skipped_invalid_npub
            + skipped_cooldown;
        let should_summarize = caller == "startup" || enqueued > 0;
        if should_summarize {
            info!(
                caller = %caller,
                cached = cached_count,
                queued = enqueued,
                skipped_age = skipped_age,
                skipped_configured = skipped_configured,
                skipped_self = skipped_self,
                skipped_connected = skipped_connected,
                skipped_retry_pending = skipped_retry_pending,
                skipped_connecting = skipped_connecting,
                skipped_no_endpoints = skipped_no_endpoints,
                skipped_invalid_npub = skipped_invalid_npub,
                skipped_cooldown = skipped_cooldown,
                skipped_total = total_skipped,
                "open-discovery sweep complete"
            );
        }
    }

    /// One-shot startup sweep: runs once after the configured settle
    /// delay, iterating the cached overlay adverts and queueing retries
    /// for any peer with a recent enough advert that we haven't already
    /// configured statically or established a link to.
    ///
    /// Gated identically to [`run_open_discovery_sweep`]: requires
    /// `node.discovery.nostr.enabled` and `policy == open`.
    async fn maybe_run_startup_open_discovery_sweep(
        &mut self,
        bootstrap: &std::sync::Arc<NostrDiscovery>,
    ) {
        if self.startup_open_discovery_sweep_done {
            return;
        }
        if !self.config.node.discovery.nostr.enabled
            || self.config.node.discovery.nostr.policy != crate::config::NostrDiscoveryPolicy::Open
        {
            // Mark done so we don't keep re-checking on every tick.
            self.startup_open_discovery_sweep_done = true;
            return;
        }
        let Some(started_at_ms) = self.nostr_discovery_started_at_ms else {
            return;
        };
        let now_ms = Self::now_ms();
        let delay_ms = self
            .config
            .node
            .discovery
            .nostr
            .startup_sweep_delay_secs
            .saturating_mul(1000);
        if now_ms < started_at_ms.saturating_add(delay_ms) {
            return;
        }

        let max_age_secs = self.config.node.discovery.nostr.startup_sweep_max_age_secs;
        self.run_open_discovery_sweep(bootstrap, Some(max_age_secs), "startup")
            .await;
        self.startup_open_discovery_sweep_done = true;
    }

    fn available_outbound_slots(&self) -> usize {
        let connection_used = self
            .connections
            .len()
            .saturating_add(self.pending_connects.len());
        let connection_slots = if self.max_connections == 0 {
            usize::MAX
        } else {
            self.max_connections.saturating_sub(connection_used)
        };

        let peer_slots = if self.max_peers == 0 {
            usize::MAX
        } else {
            self.max_peers.saturating_sub(self.peers.len())
        };

        let link_slots = if self.max_links == 0 {
            usize::MAX
        } else {
            self.max_links.saturating_sub(self.links.len())
        };

        connection_slots.min(peer_slots).min(link_slots)
    }

    pub(in crate::node) fn open_discovery_enqueue_budget(
        &self,
        configured_npubs: &HashSet<String>,
    ) -> usize {
        let current_open_discovery_active = self
            .peers
            .values()
            .filter(|peer| !configured_npubs.contains(&peer.npub()))
            .count();
        let current_open_discovery_pending = self
            .retry_pending
            .values()
            .filter(|state| !configured_npubs.contains(&state.peer_config.npub))
            .count();

        let cap_remaining = self
            .config
            .node
            .discovery
            .nostr
            .open_discovery_max_pending
            .saturating_sub(current_open_discovery_active)
            .saturating_sub(current_open_discovery_pending);

        cap_remaining.min(self.available_outbound_slots())
    }

    fn open_discovery_retry_expires_at_ms(&self, now_ms: u64) -> u64 {
        now_ms.saturating_add(
            self.config
                .node
                .discovery
                .nostr
                .advert_ttl_secs
                .saturating_mul(1000)
                .saturating_mul(OPEN_DISCOVERY_RETRY_LIFETIME_MULTIPLIER),
        )
    }

    async fn build_overlay_advert(
        &self,
        bootstrap: &std::sync::Arc<NostrDiscovery>,
    ) -> Option<OverlayAdvert> {
        if !self.config.node.discovery.nostr.enabled {
            return None;
        }

        let mut endpoints = Vec::new();
        let mut has_udp_nat = false;
        let mut has_webrtc = false;

        for handle in self.transports.values() {
            if !handle.is_operational() {
                continue;
            }

            match handle.transport_type().name {
                "udp" => {
                    let Some(cfg) = self.lookup_udp_config(handle.name()) else {
                        continue;
                    };
                    if !cfg.advertise_on_nostr() {
                        continue;
                    }
                    if cfg.is_public() {
                        // Precedence:
                        // 1. operator-supplied `external_addr` (skips STUN)
                        // 2. non-wildcard *public* `local_addr` (operator
                        //    bound to a specific public IP directly)
                        // 3. STUN auto-discovery against ephemeral socket
                        //    (also taken when bind is wildcard *or* private —
                        //    a private bind is not peer-reachable, so we
                        //    must publish the public reflexive instead)
                        // 4. loud warn + omit endpoint
                        if let Some(explicit) = cfg.external_advert_addr() {
                            endpoints.push(OverlayEndpointAdvert {
                                transport: OverlayTransportKind::Udp,
                                addr: explicit.to_string(),
                            });
                        } else {
                            match handle.local_addr() {
                                Some(addr)
                                    if !addr.ip().is_unspecified()
                                        && !is_unroutable_advert_ip(addr.ip()) =>
                                {
                                    endpoints.push(OverlayEndpointAdvert {
                                        transport: OverlayTransportKind::Udp,
                                        addr: addr.to_string(),
                                    });
                                }
                                Some(addr) => {
                                    let key = handle.transport_id().as_u32();
                                    let port = addr.port();
                                    if let Some(public) =
                                        bootstrap.learn_public_udp_addr(key, port).await
                                    {
                                        endpoints.push(OverlayEndpointAdvert {
                                            transport: OverlayTransportKind::Udp,
                                            addr: public.to_string(),
                                        });
                                    } else {
                                        warn!(
                                            transport_id = key,
                                            bind_addr = %addr,
                                            "advert: udp public=true but bind is wildcard \
                                            or private and STUN observation failed; \
                                            advertising no UDP endpoint. Either set \
                                            transports.udp.external_addr, bind to a \
                                            specific *public* IP, or ensure \
                                            node.discovery.nostr.stun_servers is reachable"
                                        );
                                    }
                                }
                                None => {}
                            }
                        }
                    } else {
                        endpoints.push(OverlayEndpointAdvert {
                            transport: OverlayTransportKind::Udp,
                            addr: "nat".to_string(),
                        });
                        has_udp_nat = true;
                    }
                }
                "webrtc" => {
                    let Some(cfg) = self.lookup_webrtc_config(handle.name()) else {
                        continue;
                    };
                    if !cfg.advertise_on_nostr() {
                        continue;
                    }
                    endpoints.push(OverlayEndpointAdvert {
                        transport: OverlayTransportKind::WebRtc,
                        addr: hex::encode(self.identity.pubkey_full().serialize()),
                    });
                    has_webrtc = true;
                }
                "tcp" => {
                    let Some(cfg) = self.lookup_tcp_config(handle.name()) else {
                        continue;
                    };
                    if !cfg.advertise_on_nostr() {
                        continue;
                    }
                    // Precedence:
                    // 1. operator-supplied `external_addr` (only path that
                    //    works on cloud-NAT setups where the public IP is
                    //    not on a host interface).
                    // 2. non-wildcard *public* `local_addr` (operator bound
                    //    to a specific public IP directly).
                    // 3. loud warn + omit endpoint (no TCP STUN equivalent).
                    //
                    // A wildcard *or* private bind is never advertised as-is
                    // — peers off-LAN can't reach a private bind, and there
                    // is no TCP STUN to discover a public reflexive.
                    if let Some(explicit) = cfg.external_advert_addr() {
                        endpoints.push(OverlayEndpointAdvert {
                            transport: OverlayTransportKind::Tcp,
                            addr: explicit.to_string(),
                        });
                    } else {
                        match handle.local_addr() {
                            Some(addr)
                                if !addr.ip().is_unspecified()
                                    && !is_unroutable_advert_ip(addr.ip()) =>
                            {
                                endpoints.push(OverlayEndpointAdvert {
                                    transport: OverlayTransportKind::Tcp,
                                    addr: addr.to_string(),
                                });
                            }
                            Some(addr) => {
                                warn!(
                                    bind_addr = %addr,
                                    "advert: tcp advertise_on_nostr=true bound to wildcard \
                                    or private IP and no transports.tcp.external_addr set; \
                                    advertising no TCP endpoint. Either set external_addr \
                                    to the public IP (recommended for cloud 1:1-NAT setups) \
                                    or bind explicitly to the public IP"
                                );
                            }
                            None => {}
                        }
                    }
                }
                "tor" => {
                    let Some(cfg) = self.lookup_tor_config(handle.name()) else {
                        continue;
                    };
                    if !cfg.advertise_on_nostr() {
                        continue;
                    }
                    if let Some(addr) = handle.onion_address() {
                        endpoints.push(OverlayEndpointAdvert {
                            transport: OverlayTransportKind::Tor,
                            addr: format!("{}:{}", addr, cfg.advertised_port()),
                        });
                    }
                }
                _ => {}
            }
        }

        if endpoints.is_empty() {
            return None;
        }

        Some(OverlayAdvert {
            identifier: ADVERT_IDENTIFIER.to_string(),
            version: ADVERT_VERSION,
            endpoints,
            signal_relays: (has_udp_nat || has_webrtc)
                .then(|| self.config.node.discovery.nostr.dm_relays.clone()),
            stun_servers: (has_udp_nat || has_webrtc)
                .then(|| self.config.node.discovery.nostr.stun_servers.clone()),
        })
    }

    async fn refresh_overlay_advert(
        &self,
        bootstrap: &std::sync::Arc<NostrDiscovery>,
    ) -> Result<(), crate::discovery::nostr::BootstrapError> {
        let advert = self.build_overlay_advert(bootstrap).await;
        bootstrap.update_local_advert(advert).await
    }

    fn lookup_udp_config(&self, transport_name: Option<&str>) -> Option<&crate::config::UdpConfig> {
        match (&self.config.transports.udp, transport_name) {
            (crate::config::TransportInstances::Single(cfg), None) => Some(cfg),
            (crate::config::TransportInstances::Named(configs), Some(name)) => configs.get(name),
            _ => None,
        }
    }

    fn lookup_tcp_config(&self, transport_name: Option<&str>) -> Option<&crate::config::TcpConfig> {
        match (&self.config.transports.tcp, transport_name) {
            (crate::config::TransportInstances::Single(cfg), None) => Some(cfg),
            (crate::config::TransportInstances::Named(configs), Some(name)) => configs.get(name),
            _ => None,
        }
    }

    fn lookup_tor_config(&self, transport_name: Option<&str>) -> Option<&crate::config::TorConfig> {
        match (&self.config.transports.tor, transport_name) {
            (crate::config::TransportInstances::Single(cfg), None) => Some(cfg),
            (crate::config::TransportInstances::Named(configs), Some(name)) => configs.get(name),
            _ => None,
        }
    }

    fn lookup_webrtc_config(
        &self,
        transport_name: Option<&str>,
    ) -> Option<&crate::config::WebRtcConfig> {
        match (&self.config.transports.webrtc, transport_name) {
            (crate::config::TransportInstances::Single(cfg), None) => Some(cfg),
            (crate::config::TransportInstances::Named(configs), Some(name)) => configs.get(name),
            _ => None,
        }
    }

    pub(in crate::node) async fn try_peer_addresses(
        &mut self,
        peer_config: &PeerConfig,
        peer_identity: PeerIdentity,
        allow_bootstrap_nat: bool,
    ) -> Result<(), NodeError> {
        let peer_node_addr = *peer_identity.node_addr();
        if self.peers.contains_key(&peer_node_addr) {
            debug!(
                npub = %peer_config.npub,
                "Peer already exists, skipping address attempts"
            );
            return Ok(());
        }

        let candidates = self.peer_address_candidates(peer_config).await;

        if candidates.is_empty() {
            if allow_bootstrap_nat && self.request_nostr_bootstrap(peer_config).await {
                return Ok(());
            }
            return Err(NodeError::NoTransportForType(format!(
                "no addresses known for {}",
                peer_config.npub
            )));
        }

        if self
            .attempt_peer_address_list(peer_config, peer_identity, allow_bootstrap_nat, &candidates)
            .await
            .is_ok()
        {
            if allow_bootstrap_nat {
                self.request_nostr_bootstrap(peer_config).await;
            }
            return Ok(());
        }

        if allow_bootstrap_nat && self.request_nostr_bootstrap(peer_config).await {
            return Ok(());
        }

        Err(NodeError::NoTransportForType(format!(
            "no operational transport for any of {}'s addresses",
            peer_config.npub
        )))
    }

    async fn try_active_peer_alternative_addresses(
        &mut self,
        peer_config: &PeerConfig,
        peer_identity: PeerIdentity,
        allow_same_path_refresh: bool,
    ) -> Result<bool, NodeError> {
        let peer_node_addr = *peer_identity.node_addr();
        let mut candidates = self.peer_address_candidates(peer_config).await;
        let same_path_refresh_needed = allow_same_path_refresh
            && (self.active_peer_needs_same_path_refresh(&peer_node_addr)
                || self
                    .peers
                    .get(&peer_node_addr)
                    .is_some_and(|peer| !peer.can_send()));
        if same_path_refresh_needed
            && let Some(candidate) = self.active_peer_current_udp_candidate(&peer_node_addr)
            && !candidates.iter().any(|existing| {
                existing.transport == candidate.transport && existing.addr == candidate.addr
            })
        {
            candidates.push(candidate);
            Self::sort_peer_address_candidates(&mut candidates);
        }
        let should_try_nostr =
            self.active_peer_should_keep_direct_retry(&peer_node_addr, peer_config);

        if candidates.is_empty() {
            if should_try_nostr && self.request_nostr_bootstrap(peer_config).await {
                return Ok(true);
            }
            return Err(NodeError::NoTransportForType(format!(
                "no addresses known for {}",
                peer_config.npub
            )));
        }

        let alternatives: Vec<_> = candidates
            .into_iter()
            .filter(|addr| {
                same_path_refresh_needed
                    || !self.active_peer_matches_candidate(&peer_node_addr, addr)
            })
            .collect();

        if alternatives.is_empty() {
            if should_try_nostr && self.request_nostr_bootstrap(peer_config).await {
                return Ok(true);
            }
            return Ok(false);
        }

        let needs_separate_nostr_attempt = should_try_nostr
            && !alternatives
                .iter()
                .any(|addr| addr.transport == "udp" && addr.addr.eq_ignore_ascii_case("nat"));
        let address_result = self
            .attempt_peer_address_list(peer_config, peer_identity, true, &alternatives)
            .await;
        let nostr_attempted =
            needs_separate_nostr_attempt && self.request_nostr_bootstrap(peer_config).await;

        match address_result {
            Ok(()) => Ok(true),
            Err(err) if nostr_attempted => {
                debug!(
                    npub = %peer_config.npub,
                    error = %err,
                    "Static active-peer direct-path alternatives failed; Nostr traversal still queued"
                );
                Ok(true)
            }
            Err(err) => Err(err),
        }
    }

    async fn peer_address_candidates(&self, peer_config: &PeerConfig) -> Vec<PeerAddress> {
        // Merge every candidate from every source we have for this peer.
        // Explicitly configured addresses keep first shot, then freshly
        // fetched overlay adverts are appended as fallback candidates. This
        // lets native peers try known LAN/nvpn/static UDP routes before
        // slower WebRTC/Nostr-discovered paths, while still racing every
        // concrete candidate that fits in the per-peer budget.
        let static_addresses = self.static_peer_addresses(peer_config);
        let overlay_addresses = self
            .nostr_peer_fallback_addresses(peer_config, &static_addresses)
            .await;

        let mut candidates = Vec::with_capacity(overlay_addresses.len() + static_addresses.len());
        for addr in overlay_addresses.into_iter().chain(static_addresses) {
            if !candidates.iter().any(|existing: &PeerAddress| {
                existing.transport == addr.transport && existing.addr == addr.addr
            }) {
                candidates.push(addr);
            }
        }

        Self::sort_peer_address_candidates(&mut candidates);

        candidates
    }

    fn sort_peer_address_candidates(candidates: &mut [PeerAddress]) {
        // Stable sort: explicit priority is the contract, and freshness only
        // breaks ties inside one priority tier. Overlay-discovered endpoints
        // are assigned lower priority than configured/static hints when both
        // exist, so operator-provided LAN routes keep first shot without
        // dropping fresh overlay candidates from the race.
        candidates.sort_by(|a, b| {
            if a.priority != b.priority {
                return a.priority.cmp(&b.priority);
            }
            match (a.seen_at_ms, b.seen_at_ms) {
                (Some(a_ts), Some(b_ts)) => b_ts.cmp(&a_ts),
                (Some(_), None) => std::cmp::Ordering::Less,
                (None, Some(_)) => std::cmp::Ordering::Greater,
                (None, None) => std::cmp::Ordering::Equal,
            }
        });
    }

    fn active_peer_matches_any_candidate(
        &self,
        peer_node_addr: &NodeAddr,
        candidates: &[PeerAddress],
    ) -> bool {
        candidates
            .iter()
            .any(|candidate| self.active_peer_matches_candidate(peer_node_addr, candidate))
    }

    pub(in crate::node) fn active_peer_candidate_is_fresh_enough_to_skip(
        &self,
        peer_node_addr: &NodeAddr,
        candidates: &[PeerAddress],
    ) -> bool {
        if !self
            .peers
            .get(peer_node_addr)
            .is_some_and(|peer| peer.can_send())
        {
            return false;
        }
        if !self.active_peer_matches_any_candidate(peer_node_addr, candidates) {
            return false;
        }
        !self.active_peer_needs_same_path_refresh(peer_node_addr)
    }

    pub(in crate::node) fn active_peer_should_keep_direct_retry(
        &self,
        peer_node_addr: &NodeAddr,
        peer_config: &PeerConfig,
    ) -> bool {
        let Some(peer) = self.peers.get(peer_node_addr) else {
            return false;
        };

        let static_addresses = self.static_peer_addresses(peer_config);
        if !static_addresses.is_empty() {
            return !self
                .active_peer_candidate_is_fresh_enough_to_skip(peer_node_addr, &static_addresses);
        }

        if peer_config.npub.is_empty() {
            return false;
        }

        if !self.config.node.discovery.nostr.enabled
            || self.config.node.discovery.nostr.policy == NostrDiscoveryPolicy::Disabled
        {
            return false;
        }

        let Some(transport_id) = peer.transport_id() else {
            return true;
        };

        if self.bootstrap_transports.contains(&transport_id) {
            return self.active_peer_needs_same_path_refresh(peer_node_addr);
        }

        let Some(transport) = self.transports.get(&transport_id) else {
            return true;
        };

        if transport.transport_type().name != "udp" {
            return true;
        }

        self.active_peer_needs_same_path_refresh(peer_node_addr)
    }

    pub(in crate::node) fn clear_retry_unless_direct_refresh_needed(
        &mut self,
        peer_node_addr: &NodeAddr,
    ) {
        let keep_retry = self
            .retry_pending
            .get(peer_node_addr)
            .map(|state| state.peer_config.clone())
            .is_some_and(|peer_config| {
                self.active_peer_should_keep_direct_retry(peer_node_addr, &peer_config)
            });

        if !keep_retry {
            self.retry_pending.remove(peer_node_addr);
        }
    }

    fn active_peer_needs_same_path_refresh(&self, peer_node_addr: &NodeAddr) -> bool {
        let Some(peer) = self.peers.get(peer_node_addr) else {
            return false;
        };
        let stale_after_ms = self
            .config
            .node
            .heartbeat_interval_secs
            .saturating_mul(1000)
            .max(1000);
        peer.idle_time(Self::now_ms()) > stale_after_ms
    }

    pub(in crate::node) fn active_peer_current_udp_candidate(
        &self,
        peer_node_addr: &NodeAddr,
    ) -> Option<PeerAddress> {
        let peer = self.peers.get(peer_node_addr)?;
        let current_addr = peer.current_addr()?;
        if let Some(transport_id) = peer.transport_id() {
            if let Some(transport) = self.transports.get(&transport_id) {
                if transport.transport_type().name != "udp" {
                    return None;
                }
            } else if !self
                .transports
                .values()
                .any(|transport| transport.transport_type().name == "udp")
            {
                return None;
            }
        } else if !self
            .transports
            .values()
            .any(|transport| transport.transport_type().name == "udp")
        {
            return None;
        }
        let socket_addr = current_addr.as_str()?.parse::<SocketAddr>().ok()?;

        Some(
            PeerAddress::with_priority("udp", socket_addr.to_string(), 240)
                .with_seen_at_ms(Self::now_ms()),
        )
    }

    pub(in crate::node) fn active_peer_matches_candidate(
        &self,
        peer_node_addr: &NodeAddr,
        candidate: &PeerAddress,
    ) -> bool {
        let Some(peer) = self.peers.get(peer_node_addr) else {
            return false;
        };
        let Some(current_addr) = peer.current_addr() else {
            return false;
        };
        if let Some(peer_transport_id) = peer.transport_id()
            && let Some((candidate_transport_id, candidate_addr)) =
                self.resolve_peer_address_for_match(candidate)
        {
            return peer_transport_id == candidate_transport_id && current_addr == &candidate_addr;
        }
        if peer
            .transport_id()
            .map(|id| self.bootstrap_transports.contains(&id))
            .unwrap_or(false)
        {
            return false;
        }
        let current_addr = current_addr.to_string();
        let current_transport = peer
            .transport_id()
            .and_then(|id| self.transports.get(&id))
            .map(|transport| transport.transport_type().name);

        candidate.addr == current_addr
            && current_transport
                .map(|transport| transport == candidate.transport)
                .unwrap_or(true)
    }

    fn configured_path_priority(
        &self,
        peer_node_addr: &NodeAddr,
        transport_id: TransportId,
        remote_addr: &TransportAddr,
    ) -> Option<u8> {
        self.configured_peer(peer_node_addr)?
            .addresses
            .iter()
            .filter_map(|candidate| {
                let (candidate_transport_id, candidate_addr) =
                    self.resolve_peer_address_for_match(candidate)?;
                (candidate_transport_id == transport_id && &candidate_addr == remote_addr)
                    .then_some(candidate.priority)
            })
            .min()
    }

    pub(in crate::node) fn alternate_path_priority_allows_replace(
        &self,
        peer_node_addr: &NodeAddr,
        candidate_transport_id: TransportId,
        candidate_addr: &TransportAddr,
    ) -> bool {
        const UNKNOWN_PATH_PRIORITY: u16 = u8::MAX as u16 + 1;

        let Some(peer) = self.peers.get(peer_node_addr) else {
            return true;
        };
        let Some(current_transport_id) = peer.transport_id() else {
            return true;
        };
        let Some(current_addr) = peer.current_addr() else {
            return true;
        };

        let current_priority = self
            .configured_path_priority(peer_node_addr, current_transport_id, current_addr)
            .map(u16::from)
            .unwrap_or(UNKNOWN_PATH_PRIORITY);
        let candidate_priority = self
            .configured_path_priority(peer_node_addr, candidate_transport_id, candidate_addr)
            .map(u16::from)
            .unwrap_or(UNKNOWN_PATH_PRIORITY);

        if candidate_priority <= current_priority {
            return true;
        }

        debug!(
            peer = %self.peer_display_name(peer_node_addr),
            current_transport_id = %current_transport_id,
            current_addr = %current_addr,
            current_priority,
            candidate_transport_id = %candidate_transport_id,
            candidate_addr = %candidate_addr,
            candidate_priority,
            "Suppressing lower-priority alternate path while current path remains healthy"
        );
        false
    }

    pub(in crate::node) fn authenticated_packet_path_allows_bookkeeping(
        &mut self,
        peer_node_addr: &NodeAddr,
        candidate_transport_id: TransportId,
        candidate_addr: &TransportAddr,
        now_ms: u64,
    ) -> bool {
        let Some(peer) = self.peers.get(peer_node_addr) else {
            return true;
        };

        if peer.transport_id() == Some(candidate_transport_id)
            && peer.current_addr() == Some(candidate_addr)
        {
            return true;
        }

        let current_path_sendable = peer.can_send();
        if !current_path_sendable
            || self.session_direct_path_blocks_direct_payload(peer_node_addr, now_ms)
        {
            return true;
        }

        self.alternate_path_priority_allows_replace(
            peer_node_addr,
            candidate_transport_id,
            candidate_addr,
        )
    }

    pub(in crate::node) fn active_peer_uses_recent_endpoint_path(
        &self,
        peer_node_addr: &NodeAddr,
        peer_config: &PeerConfig,
    ) -> bool {
        peer_config.addresses.iter().any(|addr| {
            addr.seen_at_ms.is_some() && self.active_peer_matches_candidate(peer_node_addr, addr)
        })
    }

    pub(in crate::node) fn active_peer_uses_traversal_path(
        &self,
        peer_node_addr: &NodeAddr,
        peer_config: &PeerConfig,
    ) -> bool {
        let via_bootstrap_transport = self
            .peers
            .get(peer_node_addr)
            .and_then(|peer| peer.transport_id())
            .map(|id| self.bootstrap_transports.contains(&id))
            .unwrap_or(false);

        via_bootstrap_transport
            || self.active_peer_uses_recent_endpoint_path(peer_node_addr, peer_config)
    }

    // === Control API methods ===

    /// Connect to a peer via the control API.
    ///
    /// Creates an ephemeral peer connection (not persisted to config, no
    /// auto-reconnect). Reuses the same connection path as auto-connect
    /// peers. Returns JSON data on success or an error message.
    pub(crate) async fn api_connect(
        &mut self,
        npub: &str,
        address: &str,
        transport: &str,
    ) -> Result<serde_json::Value, String> {
        let peer_config = PeerConfig {
            npub: npub.to_string(),
            alias: None,
            addresses: vec![PeerAddress::new(transport, address)],
            connect_policy: ConnectPolicy::Manual,
            auto_reconnect: false,
            discovery_fallback_transit: true,
        };

        // Pre-seed identity cache (same as initiate_peer_connections does)
        if let Ok(identity) = PeerIdentity::from_npub(npub) {
            self.peer_aliases
                .insert(*identity.node_addr(), identity.short_npub());
            self.register_identity(*identity.node_addr(), identity.pubkey_full());
        }

        self.initiate_peer_connection(&peer_config)
            .await
            .map(|()| {
                info!(
                    npub = %npub,
                    address = %address,
                    transport = %transport,
                    "API connect initiated"
                );
                serde_json::json!({
                    "npub": npub,
                    "address": address,
                    "transport": transport,
                })
            })
            .map_err(|e| e.to_string())
    }

    /// Disconnect a peer via the control API.
    ///
    /// Removes the peer and suppresses auto-reconnect.
    pub(crate) fn api_disconnect(&mut self, npub: &str) -> Result<serde_json::Value, String> {
        let peer_identity =
            PeerIdentity::from_npub(npub).map_err(|e| format!("invalid npub '{npub}': {e}"))?;
        let node_addr = *peer_identity.node_addr();

        if !self.peers.contains_key(&node_addr) {
            return Err(format!("peer not found: {npub}"));
        }

        // Remove the peer (full cleanup: sessions, indices, links, tree, bloom)
        self.remove_active_peer(&node_addr);

        // Suppress any pending auto-reconnect
        self.retry_pending.remove(&node_addr);

        info!(npub = %npub, "API disconnect completed");

        Ok(serde_json::json!({
            "npub": npub,
            "disconnected": true,
        }))
    }

    /// Adopt an already-established UDP traversal and start the normal FIPS
    /// Noise handshake over it.
    ///
    /// This is intended for integration with an external rendezvous runtime
    /// that has already completed relay signaling, STUN observation, and UDP
    /// hole punching. After handoff, the adopted socket is owned by FIPS.
    pub async fn adopt_established_traversal(
        &mut self,
        traversal: EstablishedTraversal,
    ) -> Result<BootstrapHandoffResult, NodeError> {
        debug!(
            peer_npub = %traversal.peer_npub,
            session_id = %traversal.session_id,
            remote_addr = %traversal.remote_addr,
            "adopting established traversal socket"
        );

        if !self.state.is_operational() {
            return Err(NodeError::NotStarted);
        }

        let packet_tx = self.packet_tx.clone().ok_or(NodeError::NotStarted)?;
        let peer_identity = PeerIdentity::from_npub(&traversal.peer_npub).map_err(|e| {
            NodeError::InvalidPeerNpub {
                npub: traversal.peer_npub.clone(),
                reason: e.to_string(),
            }
        })?;
        let peer_node_addr = *peer_identity.node_addr();
        if self.peers.contains_key(&peer_node_addr) {
            debug!(
                peer_npub = %traversal.peer_npub,
                "Adopting NAT traversal handoff as alternate path for already-connected peer"
            );
        }

        self.peer_aliases
            .insert(peer_node_addr, peer_identity.short_npub());
        self.register_identity(peer_node_addr, peer_identity.pubkey_full());

        let transport_id = self.allocate_transport_id();
        // Adopted ephemeral UDP transports inherit MTU + socket-buffer sizing
        // (and accept_connections / advertise flags) from the operator's
        // configured [transports.udp] when the bootstrap runtime doesn't
        // pass an explicit override. Lookup tries `transport_name` first
        // (covers the `Named` multi-listener variant) and falls back to the
        // unnamed `Single` listener, so single- and named-listener configs
        // both inherit cleanly.
        //
        // Tradeoff: `UdpConfig::default()` sets MTU 1280 (IPv6 minimum), the
        // only value guaranteed to survive arbitrary middlebox paths.
        // Inheriting a higher operator-chosen MTU means NAT-traversed flows
        // initially attempt that MTU and may black-hole on tighter paths
        // until reactive `MtuExceeded` recovery kicks in. Operators who
        // raise the primary MTU based on known-clean topology accept that
        // tradeoff; the silent drop on a too-low default was strictly
        // worse for the common case where the primary MTU is reachable.
        //
        // Bind / external address fields are cleared since the socket is
        // already bound.
        let inherited_config = traversal.transport_config.clone().unwrap_or_else(|| {
            let mut cfg = self
                .lookup_udp_config(traversal.transport_name.as_deref())
                .or_else(|| self.lookup_udp_config(None))
                .cloned()
                .unwrap_or_default();
            cfg.bind_addr = None;
            cfg.external_addr = None;
            cfg
        });
        let mut transport = crate::transport::udp::UdpTransport::new(
            transport_id,
            traversal.transport_name.clone(),
            inherited_config,
            packet_tx,
        );

        transport
            .adopt_socket_async(traversal.socket)
            .await
            .map_err(|e| NodeError::BootstrapHandoff(e.to_string()))?;

        let local_addr = transport.local_addr().ok_or_else(|| {
            NodeError::BootstrapHandoff("adopted UDP transport has no local address".into())
        })?;

        self.transports.insert(
            transport_id,
            crate::transport::TransportHandle::Udp(transport),
        );
        self.bootstrap_transports.insert(transport_id);
        self.bootstrap_transport_npubs
            .insert(transport_id, traversal.peer_npub.clone());

        let remote_addr = TransportAddr::from_string(&traversal.remote_addr.to_string());
        if let Err(err) = self
            .initiate_connection(transport_id, remote_addr.clone(), peer_identity)
            .await
        {
            self.bootstrap_transports.remove(&transport_id);
            self.bootstrap_transport_npubs.remove(&transport_id);
            if let Some(mut handle) = self.transports.remove(&transport_id) {
                let _ = handle.stop().await;
            }
            return Err(err);
        }

        info!(
            peer = %self.peer_display_name(&peer_node_addr),
            transport_id = %transport_id,
            local_addr = %local_addr,
            remote_addr = %traversal.remote_addr,
            session_id = %traversal.session_id,
            "adopted NAT traversal socket; handshake initiated"
        );

        Ok(BootstrapHandoffResult {
            transport_id,
            local_addr,
            remote_addr: traversal.remote_addr,
            peer_node_addr,
            session_id: traversal.session_id,
        })
    }
}