feat(sync): keep GRASP-08 private services out of public sync

A public mirror gains nothing from dialing a GRASP-08 private service:
the service will never admit it, and even attempting the connection
performs an AUTH exchange with a relay that only wants members. Worse,
retry machinery would hammer it indefinitely.

Approach: public instances fetch the NIP-11 document before the
WebSocket dial (`preflight_limit_hints`). When it advertises GRASP-08,
the worker returns a new `ConnectAttemptOutcome::PrivateService`
without dialing. The actor parks the relay in `private_service_relays`
(warn once, stable message tests grep for), retires all sync state
without the re-registration path, and both `register_relay` and
`schedule_connect_relay` refuse parked targets thereafter. Private
instances treat GRASP-08 peers as ordinary sync targets and skip the
probe. Session limit hints deliberately keep coming from the existing
post-connect fetch: reusing the pre-dial probe for hints would remove
the post-connect setup window whose stale-success handling
(disconnect during NIP-11 setup) is separately guaranteed and tested.

Correctness assumptions: the pre-dial NIP-11 probe is an outbound TCP
connection, so `preflight_limit_hints` re-runs the resolved outbound
target policy for event-directed URLs and skips the HTTP request
entirely on rejection - `connect()` then fails with the same policy
rejection through its own gate (tests/outbound_policy.rs stays green).
The park set is in-memory by design: a service that stops being
private becomes reachable again after a process restart at the latest.

Deliberately excluded: private-instance behavior toward GRASP-08 peers
(NIP-98 credentials on git fetches) lands separately.

Test infrastructure: `wait_for_log_line` moved from outbound_policy.rs
into the shared sync helpers; TestRelay gained a sync constructor with
identity publication disabled so log assertions about the bootstrap
connection are not confounded by user-index traffic. SetupDropRelay
now answers pre-dial NIP-11 probes directly and only runs its
drop-during-setup choreography for a fetch that arrives during a live
WebSocket session; the naughty-list scheduling test accounts for the
probe as a second accepted connection on the first attempt.

Validation: new tests/sync/outbound_auth.rs proves the park warning
appears exactly once and that, across a 2s observation window, the
private bootstrap relay is never connected to and no NIP-42
authentication occurs. cargo test --test sync -- sync::outbound_auth
sync::stale_connect_result sync::naughty_list_scheduling and
--test outbound_policy pass.

src/sync/mod.rs

@@ -1787,6 +1787,10 @@ enum ConnectAttemptOutcome {
         advertised_owner: Option<PublicKey>,
         advertised_grasp08: bool,
     },
+    /// The relay's NIP-11 advertises the GRASP-08 private-service extension
+    /// while this instance is public. Detected before the WebSocket dial, so
+    /// no connection or AUTH exchange ever happened.
+    PrivateService,
     Failed(String),
 }
 
@@ -2497,6 +2501,13 @@ pub struct SyncManager {
     /// re-log the same forbidden target. Bounded by the set of distinct relay
     /// URLs in stored/purgatory events, which the indexes already carry.
     rejected_relay_targets: HashSet<String>,
+    /// Relays whose NIP-11 advertises GRASP-08 while this instance is public.
+    ///
+    /// Laundering guard: a public mirror must not present private credentials
+    /// to such a relay nor hammer a service that will never admit it, so the
+    /// target is parked before the dial (no WebSocket, no AUTH exchange).
+    /// Held in memory only, re-probed at most once per process lifetime.
+    private_service_relays: HashSet<String>,
     /// Last exact-ID dependency recovery attempt, used to bound retries.
     dependency_refetch_attempts: Arc<std::sync::Mutex<HashMap<EventId, Instant>>>,
     /// Events relays reported during negentropy reconciliation but failed to
@@ -2636,6 +2647,7 @@ impl SyncManager {
             nip65_discovery_only_relays: HashSet::new(),
             pagination_sessions: HashMap::new(),
             rejected_relay_targets: HashSet::new(),
+            private_service_relays: HashSet::new(),
             dependency_refetch_attempts: Arc::new(std::sync::Mutex::new(HashMap::new())),
             missing_event_recovery: Arc::new(std::sync::Mutex::new(
                 missing_events::MissingEventRecoveryIndex::default(),
@@ -5276,6 +5288,16 @@ impl SyncManager {
             }
         };
 
+        // A GRASP-08 private service is not a sync target for a public
+        // instance; never re-enter the connection lifecycle for it.
+        if !self.config.private_mode && self.private_service_relays.contains(&relay_url) {
+            tracing::trace!(
+                relay = %relay_url,
+                "Skipping registration of GRASP-08 private-service relay"
+            );
+            return false;
+        }
+
         // An ordinary sync registration upgrades a connection that was first
         // opened only for NIP-65 discovery. Discovery must never downgrade an
         // existing repository source.
@@ -5404,6 +5426,13 @@ impl SyncManager {
             );
             return;
         }
+        if !self.config.private_mode && self.private_service_relays.contains(&relay_url) {
+            tracing::debug!(
+                relay = %relay_url,
+                "Suppressing connection attempt for GRASP-08 private-service relay"
+            );
+            return;
+        }
         let Some(result_tx) = self.connect_attempt_result_tx.clone() else {
             tracing::error!(relay = %relay_url, "Connection scheduler is not running");
             return;
@@ -5450,6 +5479,7 @@ impl SyncManager {
         let health_tracker = Arc::clone(&self.health_tracker);
         let semaphore = Arc::clone(&self.connect_attempt_semaphore);
         let timeout = self.health_tracker.base_backoff_secs();
+        let private_mode = self.config.private_mode;
         let Some(mut shutdown_rx) = self.shutdown_tx.as_ref().map(|sender| sender.subscribe())
         else {
             tracing::error!(relay = %relay_url, "Connection scheduler has no shutdown signal");
@@ -5464,18 +5494,29 @@ impl SyncManager {
                 return;
             };
             let outcome = tokio::select! {
-                result = connection.connect(timeout) => match result {
-                    Ok(()) => {
-                        let hints = connection.fetch_limit_hints().await;
-                        ConnectAttemptOutcome::Connected {
-                            advertised_default_limit: hints.default_limit,
-                            advertised_max_subscriptions: hints.max_subscriptions,
-                            advertised_owner: hints.owner,
-                            advertised_grasp08: hints.grasp08,
+                outcome = async {
+                    // A GRASP-08 private service must be recognized before
+                    // the dial so no WebSocket or AUTH exchange ever reaches
+                    // it. Only public instances park, so only they pay the
+                    // extra pre-dial probe; session hints still come from
+                    // the post-connect fetch below, which runs on every
+                    // attempt so they stay per-session.
+                    if !private_mode && connection.preflight_limit_hints().await.grasp08 {
+                        return ConnectAttemptOutcome::PrivateService;
+                    }
+                    match connection.connect(timeout).await {
+                        Ok(()) => {
+                            let hints = connection.fetch_limit_hints().await;
+                            ConnectAttemptOutcome::Connected {
+                                advertised_default_limit: hints.default_limit,
+                                advertised_max_subscriptions: hints.max_subscriptions,
+                                advertised_owner: hints.owner,
+                                advertised_grasp08: hints.grasp08,
+                            }
                         }
-                    },
-                    Err(error) => ConnectAttemptOutcome::Failed(error),
-                },
+                        Err(error) => ConnectAttemptOutcome::Failed(error),
+                    }
+                } => outcome,
                 _ = shutdown_rx.recv() => {
                     connection.disconnect().await;
                     return;
@@ -6299,6 +6340,31 @@ impl SyncManager {
                 }
                 self.handle_connect_or_reconnect(&result.relay_url).await;
             }
+            ConnectAttemptOutcome::PrivateService => {
+                if self.private_service_relays.insert(result.relay_url.clone()) {
+                    tracing::warn!(
+                        relay = %result.relay_url,
+                        "Relay advertises GRASP-08 private service; excluding it from public sync"
+                    );
+                }
+                // Retire the target like `complete_ended_session`, but without
+                // the re-registration path: the park is permanent for this
+                // process. No connected gauge to decrement - we never dialed.
+                self.relay_sync_index
+                    .write()
+                    .await
+                    .remove(&result.relay_url);
+                self.pending_sync_index
+                    .write()
+                    .await
+                    .remove(&result.relay_url);
+                self.connections.remove(&result.relay_url);
+                self.nip65_discovery_only_relays.remove(&result.relay_url);
+                self.health_tracker.forget_relay(&result.relay_url);
+                if let Some(ref metrics) = self.metrics {
+                    metrics.forget_relay(&result.relay_url);
+                }
+            }
             ConnectAttemptOutcome::Failed(error) => {
                 if let Some(category) = naughty_list::NaughtyListTracker::classify_error(&error) {
                     if let Some(ref naughty_list) = self.health_tracker.naughty_list() {

src/sync/relay_connection.rs

@@ -981,6 +981,26 @@ impl RelayConnection {
         parse_relay_limit_hints(&body)
     }
 
+    /// Fetch NIP-11 hints before the WebSocket dial.
+    ///
+    /// The pre-dial NIP-11 fetch is itself an outbound TCP connection, so it
+    /// must not bypass the SSRF gate: event-directed targets are authorized
+    /// first, and on rejection default hints are returned without any HTTP
+    /// request — the subsequent `connect()` then fails with the same policy
+    /// rejection through its own pre-dial check.
+    pub async fn preflight_limit_hints(&self) -> RelayLimitHints {
+        if self.source == RelayTargetSource::EventDirected
+            && self
+                .policy
+                .authorize_resolved(OutboundTargetKind::EventRelay, &self.url)
+                .await
+                .is_err()
+        {
+            return RelayLimitHints::default();
+        }
+        self.fetch_limit_hints().await
+    }
+
     /// Whether the SDK still considers this relay's WebSocket established.
     ///
     /// Connection setup performs bounded HTTP work after the handshake. The

tests/common/relay.rs

@@ -212,6 +212,23 @@ impl TestRelay {
         .await
     }
 
+    /// Start a syncing relay with user-index identity publication disabled.
+    ///
+    /// `start_with_sync` points identity publication at the bootstrap relay.
+    /// Tests making log-based assertions about the bootstrap connection use
+    /// this variant so identity-publication traffic cannot confound them.
+    pub async fn start_with_sync_without_user_index(bootstrap_relay_url: Option<String>) -> Self {
+        Self::start_internal(
+            port::reserve_port(),
+            RelayOptions {
+                bootstrap_relay_url,
+                user_index_relays: Some(String::new()),
+                ..RelayOptions::default()
+            },
+        )
+        .await
+    }
+
     /// Start a syncing relay with a caller-chosen relay-owner identity.
     ///
     /// Lets tests stage owner-signed events on other relays before this

tests/common/setup_drop_relay.rs

@@ -1,5 +1,11 @@
 //! Relay fixture that disconnects the WebSocket during its NIP-11 setup fetch.
+//!
+//! Public syncing instances also probe NIP-11 *before* dialing (to detect
+//! GRASP-08 private services); that pre-dial probe is answered immediately.
+//! Only a NIP-11 request arriving while a WebSocket session is live triggers
+//! the drop-during-setup choreography under test.
 
+use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::Arc;
 use std::time::Duration;
 
@@ -24,6 +30,7 @@ impl SetupDropRelay {
         let (dropped_tx, dropped_rx) = watch::channel(false);
         let nip11_tx = Arc::new(nip11_tx);
         let dropped_tx = Arc::new(dropped_tx);
+        let active_websockets = Arc::new(AtomicUsize::new(0));
         let (shutdown_tx, mut shutdown_rx) = oneshot::channel();
 
         let handle = tokio::spawn(async move {
@@ -35,6 +42,7 @@ impl SetupDropRelay {
                         let nip11_rx = nip11_rx.clone();
                         let dropped_tx = dropped_tx.clone();
                         let dropped_rx = dropped_rx.clone();
+                        let active_websockets = active_websockets.clone();
                         tokio::spawn(async move {
                             handle_connection(
                                 stream,
@@ -42,6 +50,7 @@ impl SetupDropRelay {
                                 nip11_rx,
                                 dropped_tx,
                                 dropped_rx,
+                                active_websockets,
                             )
                             .await;
                         });
@@ -78,6 +87,7 @@ async fn handle_connection(
     mut nip11_rx: watch::Receiver<bool>,
     dropped_tx: Arc<watch::Sender<bool>>,
     mut dropped_rx: watch::Receiver<bool>,
+    active_websockets: Arc<AtomicUsize>,
 ) {
     let mut header = [0_u8; 4096];
     let header_len = loop {
@@ -101,19 +111,25 @@ async fn handle_connection(
         let Ok(_websocket) = tokio_tungstenite::accept_async(stream).await else {
             return;
         };
+        active_websockets.fetch_add(1, Ordering::SeqCst);
         while !*nip11_rx.borrow() && nip11_rx.changed().await.is_ok() {}
         // Dropping the live socket is the behavior under test. Give the SDK a
         // bounded propagation window before allowing the HTTP setup to finish.
         drop(_websocket);
+        active_websockets.fetch_sub(1, Ordering::SeqCst);
         let _ = dropped_tx.send(true);
     } else {
         let mut request_bytes = vec![0_u8; header_len];
         if stream.read_exact(&mut request_bytes).await.is_err() {
             return;
         }
-        let _ = nip11_tx.send(true);
-        while !*dropped_rx.borrow() && dropped_rx.changed().await.is_ok() {}
-        tokio::time::sleep(Duration::from_millis(100)).await;
+        // Pre-dial NIP-11 probes (no live WebSocket) are answered without
+        // choreography; only a fetch during a live session drops it.
+        if active_websockets.load(Ordering::SeqCst) > 0 {
+            let _ = nip11_tx.send(true);
+            while !*dropped_rx.borrow() && dropped_rx.changed().await.is_ok() {}
+            tokio::time::sleep(Duration::from_millis(100)).await;
+        }
         let body = r#"{"limitation":{"max_subscriptions":20}}"#;
         let response = format!(
             "HTTP/1.1 200 OK\r\nContent-Type: application/nostr+json\r\nContent-Length: {}\r\nConnection: close\r\n\r\n{}",

tests/common/sync_helpers.rs

@@ -63,6 +63,29 @@ pub async fn wait_for_full_repo_live_coverage(relay: &TestRelay, timeout: Durati
     }
 }
 
+/// Wait until some line of a relay subprocess log satisfies the predicate.
+pub async fn wait_for_log_line<F>(
+    log_path: &std::path::Path,
+    timeout: Duration,
+    predicate: F,
+) -> bool
+where
+    F: Fn(&str) -> bool,
+{
+    let deadline = tokio::time::Instant::now() + timeout;
+    loop {
+        if let Ok(content) = tokio::fs::read_to_string(log_path).await {
+            if content.lines().any(&predicate) {
+                return true;
+            }
+        }
+        if tokio::time::Instant::now() >= deadline {
+            return false;
+        }
+        tokio::time::sleep(Duration::from_millis(100)).await;
+    }
+}
+
 // NOTE: Using rust-nostr Kind variants:
 // - Kind::GitIssue.as_u16() -> Kind::GitIssue (1621)
 // - Kind::Comment.as_u16() -> Kind::Comment (1111)

tests/outbound_policy.rs

@@ -20,12 +20,11 @@
 
 mod common;
 
-use std::path::Path;
 use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::Arc;
 use std::time::Duration;
 
-use common::{create_state_event, MockRelay, TestClient, TestRelay};
+use common::{create_state_event, wait_for_log_line, MockRelay, TestClient, TestRelay};
 use nostr_sdk::prelude::*;
 
 /// A commit hash that exists nowhere, keeping state events in purgatory so
@@ -56,25 +55,6 @@ async fn start_counting_listener() -> (u16, Arc<AtomicUsize>) {
     (port, count)
 }
 
-/// Wait until some line of the relay subprocess log satisfies the predicate.
-async fn wait_for_log_line<F>(log_path: &Path, timeout: Duration, predicate: F) -> bool
-where
-    F: Fn(&str) -> bool,
-{
-    let deadline = tokio::time::Instant::now() + timeout;
-    loop {
-        if let Ok(content) = tokio::fs::read_to_string(log_path).await {
-            if content.lines().any(&predicate) {
-                return true;
-            }
-        }
-        if tokio::time::Instant::now() >= deadline {
-            return false;
-        }
-        tokio::time::sleep(Duration::from_millis(100)).await;
-    }
-}
-
 /// Build a repository announcement with explicit clone and relay URL lists.
 fn announcement_with_urls(
     keys: &Keys,

tests/sync.rs

@@ -42,6 +42,7 @@ mod sync {
     pub mod metrics;
     pub mod naughty_list_scheduling;
     pub mod neg_concurrency;
+    pub mod outbound_auth;
     pub mod proactive_sync_plus;
     pub mod purgatory_fetch;
     pub mod reconnect_backoff;

tests/sync/naughty_list_scheduling.rs

@@ -85,15 +85,17 @@ async fn naughty_relay_is_not_scheduled_for_reconnection() {
         .await,
         "broken endpoint must be classified as naughty"
     );
-    assert_eq!(accepted.load(Ordering::SeqCst), 1, "first dial is required");
+    // The first attempt opens two connections: the pre-dial NIP-11 probe
+    // (GRASP-08 private-service detection) and the WebSocket dial itself.
+    assert_eq!(accepted.load(Ordering::SeqCst), 2, "first dial is required");
 
     let reconnect_deadline = tokio::time::Instant::now() + RECONNECT_OBSERVATION;
-    while tokio::time::Instant::now() < reconnect_deadline && accepted.load(Ordering::SeqCst) == 1 {
+    while tokio::time::Instant::now() < reconnect_deadline && accepted.load(Ordering::SeqCst) == 2 {
         tokio::time::sleep(Duration::from_millis(100)).await;
     }
     assert_eq!(
         accepted.load(Ordering::SeqCst),
-        1,
+        2,
         "a naughty relay must not receive another dial across reconnect ticks"
     );
     let log = tokio::fs::read_to_string(relay.log_path())

tests/sync/outbound_auth.rs

@@ -0,0 +1,70 @@
+//! Outbound Authentication and GRASP-08 Private-Service Sync Policy
+//!
+//! These tests cover how a syncing instance treats relays that demand
+//! authentication or advertise the GRASP-08 private-service extension:
+//!
+//! - A PUBLIC instance recognizes a GRASP-08 private service from its NIP-11
+//!   document before dialing, and parks it without any WebSocket connection
+//!   or AUTH exchange.
+
+use std::time::Duration;
+
+use crate::common::{wait_for_log_line, TestRelay};
+use nostr_sdk::prelude::*;
+
+/// The stable park warning emitted when a public instance excludes a
+/// GRASP-08 private service from sync.
+const PARK_LOG: &str = "Relay advertises GRASP-08 private service; excluding it from public sync";
+
+/// A public instance must never dial a relay whose NIP-11 advertises
+/// GRASP-08: the private service would only refuse it, and dialing would
+/// leak an AUTH exchange to a service that never admits this mirror.
+#[tokio::test]
+async fn public_instance_parks_grasp08_relay_without_dialing() {
+    let member = Keys::generate();
+    let private_service = TestRelay::start_private(&member.public_key()).await;
+    let syncing =
+        TestRelay::start_with_sync_without_user_index(Some(private_service.url().to_string()))
+            .await;
+
+    let parked = wait_for_log_line(&syncing.log_path(), Duration::from_secs(30), |line| {
+        line.contains(PARK_LOG) && line.contains(private_service.url())
+    })
+    .await;
+    assert!(
+        parked,
+        "public instance must park its GRASP-08 bootstrap relay"
+    );
+
+    // Absence over time (see relay_identity.rs for the sanctioned pattern):
+    // across a 2s observation window the parked relay is never connected to,
+    // no NIP-42 authentication happens, and the park warning is not repeated.
+    let window_end = tokio::time::Instant::now() + Duration::from_secs(2);
+    loop {
+        let log = tokio::fs::read_to_string(syncing.log_path())
+            .await
+            .unwrap_or_default();
+        assert!(
+            !log.lines()
+                .any(|line| line.contains("Connected") && line.contains(private_service.url())),
+            "parked GRASP-08 relay must never be dialed"
+        );
+        assert!(
+            !log.lines()
+                .any(|line| line.contains("Authenticated to relay")),
+            "no NIP-42 exchange may happen with a parked relay"
+        );
+        assert_eq!(
+            log.lines().filter(|line| line.contains(PARK_LOG)).count(),
+            1,
+            "park warning must be logged exactly once"
+        );
+        if tokio::time::Instant::now() >= window_end {
+            break;
+        }
+        tokio::time::sleep(Duration::from_millis(100)).await;
+    }
+
+    syncing.stop().await;
+    private_service.stop().await;
+}