feat(server): lazy-bind FIPS peer listener so fips.install doesn't

need an archipelago restart

Previously the server checked `fips0` once at startup; if the
interface wasn't up (pre-onboarding, or post-onboarding before the
user clicked Activate FIPS), the peer listener never bound and stayed
unreachable until the next archipelago restart.

Replaced with a `peer_late_bind_loop` background task: polls every
30s for an fd00::/8 address on `fips0` and binds the listener the
moment one appears. First tick fires immediately so the hot path —
fips0 already up at startup — is still zero-cost. Cancellation
cascades through the same `tokio::sync::watch` channel the main
listener uses.

Side effects:
- main.rs no longer computes peer_addr eagerly; dropped the unused
  param from serve_with_shutdown.
- FipsTransport::is_available already caches the service probe so
  the 30s poll doesn't thrash systemctl.

Covers task #21. Unblocks the first-boot + onboarding flow for
fresh ISO installs on .253.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

core/archipelago/src/main.rs

@@ -160,18 +160,9 @@ async fn main() -> Result<()> {
         .parse()
         .context("Invalid bind address")?;
 
-    // If the FIPS daemon has brought up `fips0` with a ULA address, bind a
-    // second listener there for peer-to-peer traffic. The peer listener
-    // applies a path whitelist (see server::is_peer_allowed_path) so FIPS
-    // peers can only reach signed peer endpoints, not internal surfaces.
-    // No address → no peer listener (fresh install pre-onboarding, fips
-    // service down, etc.); peers fall through to Tor until next restart.
-    let peer_addr: Option<SocketAddr> = fips::iface::fips0_ula().map(|ip| {
-        SocketAddr::new(std::net::IpAddr::V6(ip), fips::dial::PEER_PORT)
-    });
-    if let Some(pa) = peer_addr {
-        info!("FIPS peer listener will bind {}", pa);
-    }
+    // The FIPS peer listener is bound lazily by server::serve_with_shutdown
+    // on a 30s poll of fips0 — so a post-onboarding fips.install brings it
+    // online without needing an archipelago restart.
 
     // Spawn background update scheduler
     let update_data_dir = config.data_dir.clone();
@@ -223,7 +214,7 @@ async fn main() -> Result<()> {
         }
     };
 
-    server.serve_with_shutdown(addr, peer_addr, shutdown).await?;
+    server.serve_with_shutdown(addr, shutdown).await?;
 
     // Clean shutdown: remove PID marker so next startup doesn't trigger recovery
     crash_recovery::remove_pid_marker(&config.data_dir).await;

core/archipelago/src/server.rs

@@ -407,17 +407,18 @@ impl Server {
     /// Serve with a graceful shutdown signal.
     ///
     /// `main_addr` is the primary listener (historically `127.0.0.1:5678`).
-    /// `peer_addr` is an optional second listener bound to the `fips0` ULA
-    /// — when present, connections on that listener are subjected to the
-    /// peer path whitelist ([`is_peer_allowed_path`]) so FIPS peers can
-    /// reach only the signed peer-to-peer endpoints, not internal surfaces.
+    /// The main listener always comes up on `main_addr`. The FIPS peer
+    /// listener (path-filtered, bound to `fips0`'s ULA) is managed by a
+    /// late-binding task that polls every 30s: if fips0 isn't up at
+    /// startup (pre-onboarding install, legacy node pre-fips.install),
+    /// it keeps trying until the interface appears — no archipelago
+    /// restart required after the user activates FIPS.
     ///
     /// When `shutdown` completes, both listeners stop accepting and drain
     /// in-flight requests (bounded by `DRAIN_TIMEOUT`).
     pub async fn serve_with_shutdown(
         &self,
         main_addr: SocketAddr,
-        peer_addr: Option<SocketAddr>,
         shutdown: impl std::future::Future<Output = ()>,
     ) -> Result<()> {
         let active_connections = Arc::new(tokio::sync::Semaphore::new(1024));
@@ -432,28 +433,13 @@ impl Server {
             main_addr,
         ));
 
-        let peer_task = if let Some(addr) = peer_addr {
-            let listener = match TcpListener::bind(addr).await {
-                Ok(l) => l,
-                Err(e) => {
-                    warn!("FIPS peer listener bind to {} failed: {} — peers unreachable over FIPS until restart", addr, e);
-                    let _ = tx.send(true);
-                    main_task.await.ok();
-                    return Err(e.into());
-                }
-            };
-            info!("FIPS peer listener bound to {}", addr);
-            Some(tokio::spawn(accept_loop(
-                self.api_handler.clone(),
-                listener,
-                active_connections.clone(),
-                true, // peer listener: apply path filter
-                tx.subscribe(),
-                addr,
-            )))
-        } else {
-            None
-        };
+        // Peer listener: late-binding so we don't need an archipelago
+        // restart when fips0 comes up after onboarding.
+        let peer_task = tokio::spawn(peer_late_bind_loop(
+            self.api_handler.clone(),
+            active_connections.clone(),
+            tx.subscribe(),
+        ));
 
         shutdown.await;
         info!("Shutdown signal received, draining connections...");
@@ -471,15 +457,61 @@ impl Server {
         }
 
         let _ = main_task.await;
-        if let Some(t) = peer_task {
-            let _ = t.await;
-        }
+        let _ = peer_task.await;
 
         info!("Shutdown complete");
         Ok(())
     }
 }
 
+/// Poll every 30s for `fips0`'s ULA; when it appears, bind the peer
+/// listener and run the normal accept loop. If the bind fails (port
+/// already taken, permissions), log and keep retrying. Returns on
+/// shutdown. First tick fires immediately so the hot path for
+/// already-up fips0 is still zero-cost.
+async fn peer_late_bind_loop(
+    handler: Arc<ApiHandler>,
+    active_connections: Arc<tokio::sync::Semaphore>,
+    mut shutdown_rx: tokio::sync::watch::Receiver<bool>,
+) {
+    let mut interval = tokio::time::interval(std::time::Duration::from_secs(30));
+    interval.set_missed_tick_behavior(tokio::time::MissedTickBehavior::Delay);
+    loop {
+        tokio::select! {
+            _ = interval.tick() => {
+                let Some(ip) = crate::fips::iface::fips0_ula() else { continue };
+                let addr = SocketAddr::new(
+                    std::net::IpAddr::V6(ip),
+                    crate::fips::dial::PEER_PORT,
+                );
+                let listener = match TcpListener::bind(addr).await {
+                    Ok(l) => l,
+                    Err(e) => {
+                        warn!("FIPS peer listener bind {} failed: {} — retrying in 30s", addr, e);
+                        continue;
+                    }
+                };
+                info!("FIPS peer listener bound {}", addr);
+                // Once bound, serve until shutdown fires. accept_loop
+                // returns on shutdown, which also ends this outer loop.
+                accept_loop(
+                    handler,
+                    listener,
+                    active_connections,
+                    true, // peer listener: apply path filter
+                    shutdown_rx,
+                    addr,
+                )
+                .await;
+                return;
+            }
+            _ = shutdown_rx.changed() => {
+                if *shutdown_rx.borrow() { return; }
+            }
+        }
+    }
+}
+
 /// Whitelist of HTTP paths reachable via the peer-facing (FIPS) listener.
 /// Every entry is an endpoint already protected by cryptographic auth
 /// (ed25519 signature verification inside the handler, federation DID