fix federation recovery after network suspension

CHANGELOG.md

@@ -0,0 +1,6 @@
+# Changelog
+
+## v0.4.1 — 2026-09-02
+
+- `federation-net 0.3.1`: recover timed-out or failed Mainline-DHT rendezvous clients and expose network health to applications.
+- `music-dht 0.4.1`: retain temporarily unreachable contacts and serialize duplicate dial attempts with bounded backoff.

Cargo.lock

@@ -837,7 +837,7 @@ checksum = "da7c62ceae207dd37ea5b845da6a0696c799f85e97da1ab5b7910be3c1c80223"
 
 [[package]]
 name = "federation-net"
-version = "0.3.0"
+version = "0.3.1"
 dependencies = [
  "anyhow",
  "blake3",
@@ -2073,7 +2073,7 @@ dependencies = [
 
 [[package]]
 name = "music-dht"
-version = "0.4.0"
+version = "0.4.1"
 dependencies = [
  "anyhow",
  "async-trait",

Cargo.toml

@@ -13,8 +13,8 @@ rust-version = "1.97"
 repository = "https://gt.hexor.cy/ab/frid"
 
 [workspace.dependencies]
-federation-net = { path = "crates/federation-net", version = "0.3.0" }
-music-dht = { path = "crates/music-dht", version = "0.4.0" }
+federation-net = { path = "crates/federation-net", version = "0.3.1" }
+music-dht = { path = "crates/music-dht", version = "0.4.1" }
 iroh = "1"
 iroh-base = "1"
 iroh-tickets = "1"

crates/federation-net/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "federation-net"
-version = "0.3.0"
+version = "0.3.1"
 description = "Generic peer-to-peer networking engine built on Iroh"
 readme = "README.md"
 documentation = "https://docs.rs/federation-net"

crates/federation-net/src/engine.rs

@@ -4,7 +4,7 @@ use std::collections::HashMap;
 use std::fmt;
 use std::sync::atomic::{AtomicBool, AtomicU64, Ordering};
 use std::sync::{Arc, Mutex, MutexGuard, PoisonError, Weak};
-use std::time::Duration;
+use std::time::{Duration, Instant};
 
 use iroh::endpoint::{Connection, RecvStream, SendStream, VarInt, presets};
 use iroh::protocol::{AcceptError, ProtocolHandler, Router};
@@ -19,6 +19,7 @@ use tracing::{debug, info, warn};
 use crate::config::NetworkConfig;
 use crate::error::{NetworkError, Result};
 use crate::event::{ConnectionDirection, NetworkEvent, NetworkEventReceiver};
+use crate::health::{NetworkHealthSnapshot, NetworkHealthState};
 use crate::identity;
 use crate::protocol::{
     ALPN, Handshake, HandshakeAck, HandshakeErrorCode, MAX_HANDSHAKE_FRAME_SIZE,
@@ -50,6 +51,12 @@ const REJECT_LINGER: Duration = Duration::from_secs(3);
 const SHUTDOWN_TASK_GRACE: Duration = Duration::from_secs(5);
 /// Upper bound of the rendezvous round delay while no peer is connected yet.
 const RENDEZVOUS_LONELY_INTERVAL: Duration = Duration::from_secs(15);
+/// A stuck Mainline-DHT operation must not stall discovery forever.
+const RENDEZVOUS_ROUND_TIMEOUT: Duration = Duration::from_secs(30);
+/// Recreate the Mainline-DHT client after this many consecutive failures.
+const RENDEZVOUS_REBUILD_AFTER_FAILURES: u32 = 2;
+/// Recommend an application-owned full restart after sustained discovery failure.
+const RENDEZVOUS_RESTART_AFTER_FAILURES: u32 = 4;
 /// Capacity of the queue of accepted-but-not-yet-consumed incoming byte
 /// streams, per stream protocol. A full queue delays the handshake ack of
 /// further incoming streams (natural backpressure).
@@ -260,6 +267,27 @@ struct StreamAcceptorSlot {
     receiver: Option<mpsc::Receiver<ByteStream>>,
 }
 
+#[derive(Debug)]
+struct RendezvousHealth {
+    last_success: Option<Instant>,
+    consecutive_failures: u32,
+    consecutive_peer_dial_failures: u32,
+    client_restarts: u64,
+    last_error: Option<String>,
+}
+
+impl RendezvousHealth {
+    fn new() -> Self {
+        Self {
+            last_success: None,
+            consecutive_failures: 0,
+            consecutive_peer_dial_failures: 0,
+            client_restarts: 0,
+            last_error: None,
+        }
+    }
+}
+
 fn alpn_display(alpn: &[u8]) -> String {
     String::from_utf8_lossy(alpn).into_owned()
 }
@@ -276,6 +304,7 @@ struct Shared<M> {
     tasks: Mutex<JoinSet<()>>,
     next_generation: AtomicU64,
     shutting_down: AtomicBool,
+    rendezvous_health: Mutex<Option<RendezvousHealth>>,
     /// Broadcasts the start of the shutdown to long-running background
     /// loops so they can stop promptly instead of being aborted.
     shutdown_signal: watch::Sender<bool>,
@@ -294,6 +323,97 @@ impl<M: Message> Shared<M> {
         }
     }
 
+    fn record_rendezvous_success(&self) {
+        if let Some(health) = lock(&self.rendezvous_health).as_mut() {
+            health.last_success = Some(Instant::now());
+            health.consecutive_failures = 0;
+            health.last_error = None;
+        }
+    }
+
+    fn record_rendezvous_failure(&self, error: String) -> u32 {
+        let mut guard = lock(&self.rendezvous_health);
+        let Some(health) = guard.as_mut() else {
+            return 0;
+        };
+        health.consecutive_failures = health.consecutive_failures.saturating_add(1);
+        health.last_error = Some(error);
+        health.consecutive_failures
+    }
+
+    fn record_rendezvous_restart(&self) {
+        if let Some(health) = lock(&self.rendezvous_health).as_mut() {
+            health.client_restarts = health.client_restarts.saturating_add(1);
+        }
+    }
+
+    fn record_peer_connection_success(&self) {
+        if let Some(health) = lock(&self.rendezvous_health).as_mut() {
+            health.consecutive_peer_dial_failures = 0;
+        }
+    }
+
+    fn record_rendezvous_peer_dials(&self, candidates: usize, attempts: usize, successes: usize) {
+        let mut guard = lock(&self.rendezvous_health);
+        let Some(health) = guard.as_mut() else {
+            return;
+        };
+        if candidates == 0 || successes > 0 {
+            health.consecutive_peer_dial_failures = 0;
+        } else if attempts > 0 {
+            health.consecutive_peer_dial_failures =
+                health.consecutive_peer_dial_failures.saturating_add(1);
+            health.last_error = Some(format!(
+                "failed to connect to all {attempts} peer(s) discovered by rendezvous"
+            ));
+        }
+    }
+
+    fn health(&self) -> NetworkHealthSnapshot {
+        let connected_peers = lock(&self.peers).len();
+        let guard = lock(&self.rendezvous_health);
+        let Some(health) = guard.as_ref() else {
+            return NetworkHealthSnapshot {
+                state: if connected_peers == 0 {
+                    NetworkHealthState::Discovering
+                } else {
+                    NetworkHealthState::Healthy
+                },
+                connected_peers,
+                rendezvous_enabled: false,
+                consecutive_rendezvous_failures: 0,
+                consecutive_peer_dial_failures: 0,
+                rendezvous_restarts: 0,
+                last_rendezvous_success_ago: None,
+                last_rendezvous_error: None,
+                restart_recommended: false,
+            };
+        };
+        let restart_recommended = connected_peers == 0
+            && (health.consecutive_failures >= RENDEZVOUS_RESTART_AFTER_FAILURES
+                || health.consecutive_peer_dial_failures >= RENDEZVOUS_RESTART_AFTER_FAILURES);
+        let state = if restart_recommended {
+            NetworkHealthState::Degraded
+        } else if health.consecutive_failures > 0 || health.consecutive_peer_dial_failures > 0 {
+            NetworkHealthState::Recovering
+        } else if health.last_success.is_some() {
+            NetworkHealthState::Healthy
+        } else {
+            NetworkHealthState::Discovering
+        };
+        NetworkHealthSnapshot {
+            state,
+            connected_peers,
+            rendezvous_enabled: true,
+            consecutive_rendezvous_failures: health.consecutive_failures,
+            consecutive_peer_dial_failures: health.consecutive_peer_dial_failures,
+            rendezvous_restarts: health.client_restarts,
+            last_rendezvous_success_ago: health.last_success.map(|at| at.elapsed()),
+            last_rendezvous_error: health.last_error.clone(),
+            restart_recommended,
+        }
+    }
+
     /// Delivers an event to the application.
     ///
     /// The channel is bounded; if it is full this awaits until the
@@ -335,6 +455,7 @@ impl<M: Message> Shared<M> {
             generation,
         };
         let replaced = lock(&self.peers).insert(peer_id, state);
+        self.record_peer_connection_success();
         if let Some(old) = replaced {
             debug!(peer = %peer_id, "replacing existing connection");
             old.connection
@@ -786,39 +907,92 @@ impl<M: Message> Shared<M> {
 /// Failures of a single round or dial are logged and retried on the next
 /// round; the loop only ends when the engine shuts down (the task is
 /// aborted).
-async fn rendezvous_loop<M: Message>(
-    shared: Arc<Shared<M>>,
-    client: RendezvousClient,
-    config: RendezvousConfig,
-) {
+async fn rendezvous_loop<M: Message>(shared: Arc<Shared<M>>, config: RendezvousConfig) {
     let mut shutdown = shared.shutdown_signal.subscribe();
     // Give the endpoint a moment to learn its relay and direct addresses so
     // the very first published record is already dialable.
     let _ = timeout(shared.config.request_timeout, shared.endpoint.online()).await;
     let self_id = shared.endpoint.id();
+    let mut client = None;
     loop {
         if shared.is_shutting_down() {
             return;
         }
+        if client.is_none() {
+            match RendezvousClient::new(shared.config.network_id, &config) {
+                Ok(new_client) => client = Some(new_client),
+                Err(err) => {
+                    let failures = shared.record_rendezvous_failure(err.to_string());
+                    warn!(error = %err, failures, "failed to start peer rendezvous; retrying");
+                }
+            }
+        }
         let round = async {
+            let Some(active_client) = client.as_ref() else {
+                return;
+            };
             let addr = shared.endpoint.addr();
             let self_addr = (!addr.is_empty()).then_some(addr);
-            match client.round(self_addr, now_ms()).await {
-                Ok(peers) => {
-                    for peer_addr in peers {
+            if self_addr.is_none() {
+                let failures = shared.record_rendezvous_failure(
+                    "local endpoint has no dialable address".to_string(),
+                );
+                debug!(failures, "rendezvous waiting for a dialable local address");
+                return;
+            }
+            match timeout(
+                RENDEZVOUS_ROUND_TIMEOUT,
+                active_client.round(self_addr, now_ms()),
+            )
+            .await
+            {
+                Ok(Ok(round)) => {
+                    let candidates = round.peers.len();
+                    let mut attempts = 0;
+                    let mut successes = 0;
+                    for peer_addr in round.peers {
                         let peer = peer_addr.id;
                         if peer == self_id || lock(&shared.peers).contains_key(&peer) {
                             continue;
                         }
                         debug!(peer = %peer, "rendezvous discovered a peer; connecting");
-                        if let Err(err) = shared.connect_to_addr(peer_addr).await {
-                            // Stale entries (peers that left) fail here; they
-                            // age out of the record by TTL.
-                            debug!(peer = %peer, error = %err, "rendezvous connect attempt failed");
+                        attempts += 1;
+                        match shared.connect_to_addr(peer_addr).await {
+                            Ok(_) => successes += 1,
+                            Err(err) => {
+                                // Stale entries (peers that left) fail here;
+                                // they age out of the record by TTL.
+                                debug!(peer = %peer, error = %err, "rendezvous connect attempt failed");
+                            }
                         }
                     }
+                    if let Some(error) = round.publish_error {
+                        let failures = shared.record_rendezvous_failure(error.clone());
+                        debug!(%error, failures, "rendezvous publish failed");
+                    } else {
+                        shared.record_rendezvous_success();
+                    }
+                    shared.record_rendezvous_peer_dials(candidates, attempts, successes);
                 }
-                Err(err) => debug!(error = %err, "rendezvous round failed"),
+                Ok(Err(err)) => {
+                    let failures = shared.record_rendezvous_failure(err.to_string());
+                    debug!(error = %err, failures, "rendezvous round failed");
+                }
+                Err(_) => {
+                    let failures = shared.record_rendezvous_failure(format!(
+                        "rendezvous round timed out after {}s",
+                        RENDEZVOUS_ROUND_TIMEOUT.as_secs()
+                    ));
+                    warn!(failures, "rendezvous round timed out");
+                }
+            }
+            let failures = lock(&shared.rendezvous_health)
+                .as_ref()
+                .map_or(0, |health| health.consecutive_failures);
+            if failures >= RENDEZVOUS_REBUILD_AFTER_FAILURES {
+                client = None;
+                shared.record_rendezvous_restart();
+                info!(failures, "rebuilding the rendezvous client");
             }
         };
         tokio::select! {
@@ -960,6 +1134,7 @@ impl<M: Message> NetworkEngine<M> {
         config: NetworkConfig,
         secret_key: SecretKey,
     ) -> Result<(Self, NetworkEventReceiver<M>)> {
+        let rendezvous_enabled = config.rendezvous.is_some();
         let endpoint = Endpoint::builder(presets::N0)
             .secret_key(secret_key)
             .bind()
@@ -992,6 +1167,7 @@ impl<M: Message> NetworkEngine<M> {
             tasks: Mutex::new(JoinSet::new()),
             next_generation: AtomicU64::new(0),
             shutting_down: AtomicBool::new(false),
+            rendezvous_health: Mutex::new(rendezvous_enabled.then(RendezvousHealth::new)),
             shutdown_signal: watch::Sender::new(false),
         });
         let handler = FederationProtocol {
@@ -1015,17 +1191,10 @@ impl<M: Message> NetworkEngine<M> {
         let router = router_builder.spawn();
         *lock(&shared.router) = Some(router);
         if let Some(rendezvous) = shared.config.rendezvous.clone() {
-            match RendezvousClient::new(shared.config.network_id, &rendezvous) {
-                Ok(client) => {
-                    let loop_shared = shared.clone();
-                    shared.spawn_task(async move {
-                        rendezvous_loop(loop_shared, client, rendezvous).await;
-                    });
-                }
-                // Rendezvous is a convenience; the engine stays usable via
-                // tickets even when the DHT client cannot start.
-                Err(err) => warn!(error = %err, "peer rendezvous disabled"),
-            }
+            let loop_shared = shared.clone();
+            shared.spawn_task(async move {
+                rendezvous_loop(loop_shared, rendezvous).await;
+            });
         }
         info!(
             endpoint_id = %endpoint_id,
@@ -1257,6 +1426,11 @@ impl<M: Message> NetworkEngine<M> {
         lock(&self.shared.peers).keys().copied().collect()
     }
 
+    /// Returns a point-in-time snapshot of transport and rendezvous health.
+    pub fn health(&self) -> NetworkHealthSnapshot {
+        self.shared.health()
+    }
+
     /// Returns `true` if there is an active connection to `peer`.
     pub fn is_connected(&self, peer: EndpointId) -> bool {
         lock(&self.shared.peers).contains_key(&peer)

crates/federation-net/src/health.rs

@@ -0,0 +1,62 @@
+//! Point-in-time health information for the transport and rendezvous loop.
+
+use std::fmt;
+use std::time::Duration;
+
+/// Coarse health state of a running network engine.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum NetworkHealthState {
+    /// The engine is starting or has no discovery mechanism configured.
+    Discovering,
+    /// Transport and rendezvous maintenance are operating normally.
+    Healthy,
+    /// A recent rendezvous operation failed and is being retried.
+    Recovering,
+    /// Repeated rendezvous failures indicate that the engine should be restarted.
+    Degraded,
+}
+
+impl NetworkHealthState {
+    /// Returns a compact stable label for logs and user interfaces.
+    pub fn as_str(self) -> &'static str {
+        match self {
+            Self::Discovering => "discovering",
+            Self::Healthy => "healthy",
+            Self::Recovering => "recovering",
+            Self::Degraded => "degraded",
+        }
+    }
+}
+
+impl fmt::Display for NetworkHealthState {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(self.as_str())
+    }
+}
+
+/// Point-in-time health snapshot of a running network engine.
+///
+/// Zero connected peers is not itself an error: a network may legitimately
+/// contain only one online node. [`Self::restart_recommended`] is therefore
+/// based on repeated discovery failures as well as the absence of peers.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct NetworkHealthSnapshot {
+    /// Coarse state suitable for logs and user interfaces.
+    pub state: NetworkHealthState,
+    /// Number of currently connected peers.
+    pub connected_peers: usize,
+    /// Whether Mainline-DHT rendezvous discovery is enabled.
+    pub rendezvous_enabled: bool,
+    /// Consecutive failed or timed-out rendezvous rounds.
+    pub consecutive_rendezvous_failures: u32,
+    /// Consecutive rendezvous rounds in which every discovered peer dial failed.
+    pub consecutive_peer_dial_failures: u32,
+    /// Number of times the rendezvous client was rebuilt after failures.
+    pub rendezvous_restarts: u64,
+    /// Time elapsed since the most recent successful rendezvous round.
+    pub last_rendezvous_success_ago: Option<Duration>,
+    /// Most recent rendezvous error, if a later successful round has not cleared it.
+    pub last_rendezvous_error: Option<String>,
+    /// Whether an application-owned full service restart is advisable.
+    pub restart_recommended: bool,
+}

crates/federation-net/src/lib.rs

@@ -55,6 +55,7 @@ mod config;
 mod engine;
 mod error;
 mod event;
+mod health;
 mod identity;
 mod protocol;
 mod rendezvous;
@@ -71,6 +72,7 @@ pub use engine::{
 };
 pub use error::{NetworkError, Result};
 pub use event::{ConnectionDirection, NetworkEvent, NetworkEventReceiver};
+pub use health::{NetworkHealthSnapshot, NetworkHealthState};
 pub use protocol::{ALPN, NetworkId, PROTOCOL_VERSION, SchemaId};
 pub use rendezvous::RENDEZVOUS_RECORD_VERSION;
 pub use rendezvous::{DEFAULT_RENDEZVOUS_ENTRY_TTL, DEFAULT_RENDEZVOUS_INTERVAL, RendezvousConfig};

crates/federation-net/src/rendezvous.rs

@@ -27,7 +27,7 @@ use iroh::{EndpointAddr, EndpointId};
 use mainline::async_dht::AsyncDht;
 use mainline::{Dht, MutableItem, SigningKey};
 use serde::{Deserialize, Serialize};
-use tracing::{debug, warn};
+use tracing::debug;
 
 use crate::error::{NetworkError, Result};
 use crate::protocol::NetworkId;
@@ -171,6 +171,12 @@ pub(crate) struct RendezvousClient {
     entry_ttl: Duration,
 }
 
+/// Result of one read/merge/publish cycle.
+pub(crate) struct RendezvousRound {
+    pub(crate) peers: Vec<EndpointAddr>,
+    pub(crate) publish_error: Option<String>,
+}
+
 impl RendezvousClient {
     /// Binds a mainline DHT client for the rendezvous record of `network_id`.
     pub(crate) fn new(network_id: NetworkId, config: &RendezvousConfig) -> Result<Self> {
@@ -201,7 +207,7 @@ impl RendezvousClient {
         &self,
         self_addr: Option<EndpointAddr>,
         now_ms: u64,
-    ) -> Result<Vec<EndpointAddr>> {
+    ) -> Result<RendezvousRound> {
         let public_key = self.key.verifying_key().to_bytes();
         let mut items = self.dht.get_mutable(&public_key, None, None);
         let mut seen = Vec::new();
@@ -222,21 +228,28 @@ impl RendezvousClient {
         let publish = self_entry.is_some();
         let merged = merge_entries(seen, self_entry, now_ms, self.entry_ttl);
 
-        if publish {
+        let publish_error = if publish {
             let encoded = encode_record_capped(merged.clone())?;
             // Strictly newer than every instance seen this round; concurrent
             // writers race, but merging on read makes lost updates benign.
             let item = MutableItem::new(self.key.clone(), &encoded, max_seq + 1, None);
-            if let Err(err) = self.dht.put_mutable(item, None).await {
-                warn!(error = %err, "failed to publish the rendezvous record");
-            }
-        }
+            self.dht
+                .put_mutable(item, None)
+                .await
+                .err()
+                .map(|err| format!("failed to publish the rendezvous record: {err}"))
+        } else {
+            None
+        };
 
-        Ok(merged
-            .into_iter()
-            .map(|entry| entry.addr)
-            .filter(|addr| Some(addr.id) != self_id)
-            .collect())
+        Ok(RendezvousRound {
+            peers: merged
+                .into_iter()
+                .map(|entry| entry.addr)
+                .filter(|addr| Some(addr.id) != self_id)
+                .collect(),
+            publish_error,
+        })
     }
 }
 

crates/music-dht/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "music-dht"
-version = "0.4.0"
+version = "0.4.1"
 description = "Distributed music library search: a Kademlia-style DHT on top of federation-net"
 readme = "README.md"
 documentation = "https://docs.rs/music-dht"

crates/music-dht/src/lib.rs

@@ -133,6 +133,7 @@ pub use service::{
 
 // Re-exported types from the transport layer that appear in this API.
 pub use federation_net::{
-    ByteStream, ByteStreamConnectionStats, ConnectionPathKind, EndpointAddr, EndpointId, NetworkId,
-    PeerTicket, RecvStream, RendezvousConfig, SecretKey, SendStream, StreamAcceptor,
+    ByteStream, ByteStreamConnectionStats, ConnectionPathKind, EndpointAddr, EndpointId,
+    NetworkHealthSnapshot, NetworkHealthState, NetworkId, PeerTicket, RecvStream, RendezvousConfig,
+    SecretKey, SendStream, StreamAcceptor,
 };

crates/music-dht/src/node.rs

@@ -36,8 +36,8 @@ fn lock<T>(mutex: &Mutex<T>) -> MutexGuard<'_, T> {
 const DIAL_BACKOFF_BASE: Duration = Duration::from_secs(30);
 /// Upper bound of the dial backoff.
 const DIAL_BACKOFF_MAX: Duration = Duration::from_secs(10 * 60);
-/// Consecutive failed dials after which a contact is evicted entirely.
-const DIAL_FAILURES_BEFORE_EVICT: u32 = 5;
+/// Consecutive failed dials after which a contact is considered cold.
+const DIAL_FAILURES_BEFORE_COLD: u32 = 5;
 
 /// Dial-failure state of one currently unreachable contact.
 #[derive(Debug, Clone, Copy)]
@@ -97,6 +97,8 @@ pub(crate) struct Node {
     exchange_sent: Mutex<HashSet<EndpointId>>,
     /// Contacts that recently failed to dial, with their backoff state.
     dial_failures: Mutex<HashMap<EndpointId, DialFailure>>,
+    /// Serializes on-demand connection attempts to the same contact.
+    dial_locks: Mutex<HashMap<EndpointId, Arc<tokio::sync::Mutex<()>>>>,
     events: Mutex<Option<mpsc::Sender<MusicDhtEvent>>>,
     /// Set once the post-startup republish has been triggered.
     initial_republish_done: AtomicBool,
@@ -123,6 +125,7 @@ impl Node {
             hello_sent: Mutex::new(HashSet::new()),
             exchange_sent: Mutex::new(HashSet::new()),
             dial_failures: Mutex::new(HashMap::new()),
+            dial_locks: Mutex::new(HashMap::new()),
             events: Mutex::new(Some(events)),
             initial_republish_done: AtomicBool::new(false),
             shutting_down: AtomicBool::new(false),
@@ -478,6 +481,18 @@ impl Node {
         if self.engine.is_connected(contact.peer_id) {
             return Ok(contact.peer_id);
         }
+        let dial_lock = lock(&self.dial_locks)
+            .entry(contact.peer_id)
+            .or_insert_with(|| Arc::new(tokio::sync::Mutex::new(())))
+            .clone();
+        let _dial_guard = dial_lock.lock().await;
+        self.ensure_running()?;
+        if self.engine.is_connected(contact.peer_id) {
+            return Ok(contact.peer_id);
+        }
+        if self.dial_backoff_active(&contact.peer_id, now_ms()) {
+            return Err(MusicDhtError::Timeout);
+        }
         let ticket: PeerTicket = contact
             .ticket
             .parse()
@@ -493,7 +508,7 @@ impl Node {
                 Ok(peer)
             }
             Err(err) => {
-                self.note_dial_failure(contact).await;
+                self.note_dial_failure(contact);
                 Err(err)
             }
         }
@@ -519,35 +534,36 @@ impl Node {
         }
     }
 
-    /// Records a failed dial; after [`DIAL_FAILURES_BEFORE_EVICT`] failures
-    /// in a row the contact is dropped from the routing table and the
-    /// database (gossip re-adds it with a clean slate if it comes back).
-    async fn note_dial_failure(&self, contact: &NodeContact) {
+    /// Records a failed dial and increases its bounded retry backoff.
+    ///
+    /// The contact remains in memory and durable storage: temporary network
+    /// loss or system sleep must not erase the only route back to a peer.
+    fn note_dial_failure(&self, contact: &NodeContact) {
         let consecutive = {
             let mut failures = lock(&self.dial_failures);
             let failure = failures.entry(contact.peer_id).or_insert(DialFailure {
                 consecutive: 0,
                 last_attempt_ms: 0,
             });
-            failure.consecutive += 1;
+            failure.consecutive = failure.consecutive.saturating_add(1);
             failure.last_attempt_ms = now_ms();
             failure.consecutive
         };
-        if consecutive < DIAL_FAILURES_BEFORE_EVICT {
+        if consecutive == DIAL_FAILURES_BEFORE_COLD {
+            info!(
+                peer = %contact.peer_id,
+                consecutive,
+                backoff_s = dial_backoff(consecutive).as_secs(),
+                "DHT contact remains unavailable; retaining it for later recovery"
+            );
+        } else {
             debug!(
                 peer = %contact.peer_id,
                 consecutive,
                 backoff_s = dial_backoff(consecutive).as_secs(),
                 "dial failed; backing off"
             );
-            return;
         }
-        lock(&self.dial_failures).remove(&contact.peer_id);
-        lock(&self.routing).remove(&contact.peer_id);
-        if let Err(err) = self.db.delete_known_peer(contact.peer_id).await {
-            warn!(error = %err, "failed to delete evicted peer from the database");
-        }
-        info!(peer = %contact.peer_id, "evicted unreachable DHT contact");
     }
 
     /// Sends one request and awaits its response, cleaning up the pending

crates/music-dht/src/service.rs

@@ -5,8 +5,8 @@ use std::sync::Arc;
 use std::time::{Duration, Instant};
 
 use federation_net::{
-    ByteStream, EndpointAddr, EndpointId, NetworkConfig, NetworkEngine, NetworkId, PeerTicket,
-    SchemaId, SecretKey, Signature, StreamAcceptor,
+    ByteStream, EndpointAddr, EndpointId, NetworkConfig, NetworkEngine, NetworkHealthSnapshot,
+    NetworkId, PeerTicket, SchemaId, SecretKey, Signature, StreamAcceptor,
 };
 use tokio::sync::mpsc;
 use tokio::task::JoinHandle;
@@ -375,6 +375,11 @@ impl MusicDhtService {
         self.node.engine.connected_peers()
     }
 
+    /// Returns a point-in-time snapshot of transport and rendezvous health.
+    pub fn network_health(&self) -> NetworkHealthSnapshot {
+        self.node.engine.health()
+    }
+
     /// Returns `true` if a transport connection to `peer` is open.
     pub fn is_connected(&self, peer: EndpointId) -> bool {
         self.node.engine.is_connected(peer)