fix(server): web UI listens on IPv6 — the mesh could never load it

The mesh is IPv6-only; the main web listener bound 0.0.0.0 only, so a
phone reaching a node over its fips0 ULA got RST on :80
(ERR_CONNECTION_ABORTED) — UI over mesh was structurally impossible.
Confirmed 2026-07-26 on framework-pt: v4:80 = 200, v6:80 = refused.
Mirror an IPv4-any main listener with a V6ONLY [::] socket on the same
port; V6ONLY so it coexists with the v4 listener regardless of
net.ipv6.bindv6only.

Also: fips.yaml generator carries the fast-reconnect profile (validated
live on framework-pt since 2026-07-24; snapshot tests updated).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

core/archipelago/src/fips/config.rs

@@ -48,6 +48,30 @@ pub struct FipsConfig {
 pub struct NodeSection {
     pub identity: IdentitySection,
     pub discovery: DiscoverySection,
+    pub retry: RetrySection,
+    pub rate_limit: RateLimitSection,
+}
+
+/// Fast-reconnect profile (`node.retry.*`). Upstream defaults (5s base
+/// doubling to 300s) are tuned for stable always-on links; a node redialing
+/// a recycled anchor sat off-mesh for ~90s. Field names verified live on
+/// 2026-07-24: a daemon restarted with these keys in fips.yaml and peered.
+#[derive(Debug, Clone, PartialEq, Serialize)]
+pub struct RetrySection {
+    pub base_interval_secs: u64,
+    pub max_backoff_secs: u64,
+    pub max_retries: u32,
+}
+
+/// Session-handshake resend pacing (`node.rate_limit.*`). Stock 1s x2.0
+/// gaps out to 8-16s between resends exactly when a route has just
+/// appeared; 400ms x1.5 keeps continuous coverage through the connect
+/// window (phone measured session-after-route: 225ms).
+#[derive(Debug, Clone, PartialEq, Serialize)]
+pub struct RateLimitSection {
+    pub handshake_resend_interval_ms: u64,
+    pub handshake_resend_backoff: f64,
+    pub handshake_max_resends: u32,
 }
 
 #[derive(Debug, Clone, PartialEq, Serialize)]
@@ -60,6 +84,14 @@ pub struct IdentitySection {
 
 #[derive(Debug, Clone, PartialEq, Serialize)]
 pub struct DiscoverySection {
+    /// Lookup completion timeout. Lookups fired while the tree position is
+    /// still settling are doomed; failing them fast (5s, not 10s) lets the
+    /// 1s-backoff retry find the route the moment it exists.
+    pub timeout_secs: u64,
+    pub backoff_base_secs: u64,
+    pub backoff_max_secs: u64,
+    pub retry_interval_secs: u64,
+    pub max_attempts: u8,
     pub lan: LanDiscoverySection,
 }
 
@@ -123,8 +155,23 @@ impl Default for FipsConfig {
             node: NodeSection {
                 identity: IdentitySection { persistent: true },
                 discovery: DiscoverySection {
+                    timeout_secs: 5,
+                    backoff_base_secs: 1,
+                    backoff_max_secs: 30,
+                    retry_interval_secs: 2,
+                    max_attempts: 3,
                     lan: LanDiscoverySection { enabled: true },
                 },
+                retry: RetrySection {
+                    base_interval_secs: 1,
+                    max_backoff_secs: 30,
+                    max_retries: 30,
+                },
+                rate_limit: RateLimitSection {
+                    handshake_resend_interval_ms: 400,
+                    handshake_resend_backoff: 1.5,
+                    handshake_max_resends: 10,
+                },
             },
             tun: TunSection {
                 enabled: true,
@@ -318,8 +365,21 @@ node:
   identity:
     persistent: true
   discovery:
+    timeout_secs: 5
+    backoff_base_secs: 1
+    backoff_max_secs: 30
+    retry_interval_secs: 2
+    max_attempts: 3
     lan:
       enabled: true
+  retry:
+    base_interval_secs: 1
+    max_backoff_secs: 30
+    max_retries: 30
+  rate_limit:
+    handshake_resend_interval_ms: 400
+    handshake_resend_backoff: 1.5
+    handshake_max_resends: 10
 tun:
   enabled: true
   name: fips0

core/archipelago/src/server.rs

@@ -988,6 +988,43 @@ impl Server {
             main_addr,
         ));
 
+        // The mesh is IPv6-only: a phone reaching the node over its fips0
+        // ULA lands on port 80 over v6, where a 0.0.0.0 listener never
+        // answers — the UI was structurally unreachable over the mesh
+        // (RST -> ERR_CONNECTION_ABORTED, confirmed 2026-07-26: v4:80 = 200,
+        // v6:80 = refused). Mirror an IPv4-any main listener with a
+        // V6ONLY [::] socket on the same port — v6-only so it coexists
+        // with the v4 listener regardless of net.ipv6.bindv6only.
+        let v4_any_port = match main_addr {
+            SocketAddr::V4(v4) if v4.ip().is_unspecified() => Some(v4.port()),
+            _ => None,
+        };
+        let v6_task = if let Some(port) = v4_any_port {
+            let v6_addr = SocketAddr::new(
+                std::net::IpAddr::V6(std::net::Ipv6Addr::UNSPECIFIED),
+                port,
+            );
+            match bind_v6_only(v6_addr) {
+                Ok(listener) => {
+                    info!("IPv6 web listener bound {} (mesh ULA reachable)", v6_addr);
+                    Some(tokio::spawn(accept_loop(
+                        self.api_handler.clone(),
+                        listener,
+                        active_connections.clone(),
+                        false, // same semantics as the main listener
+                        tx.subscribe(),
+                        v6_addr,
+                    )))
+                }
+                Err(e) => {
+                    warn!("IPv6 web listener bind {} failed: {} — UI stays v4-only", v6_addr, e);
+                    None
+                }
+            }
+        } 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(
@@ -1012,6 +1049,9 @@ impl Server {
         }
 
         let _ = main_task.await;
+        if let Some(t) = v6_task {
+            let _ = t.await;
+        }
         let _ = peer_task.await;
 
         info!("Shutdown complete");
@@ -1019,6 +1059,24 @@ impl Server {
     }
 }
 
+/// Bind a V6ONLY `[::]` TCP listener. V6ONLY is set explicitly so the
+/// socket never claims the IPv4 side (which the main listener owns) —
+/// without it, Linux hosts with `net.ipv6.bindv6only=0` would fail with
+/// EADDRINUSE.
+fn bind_v6_only(addr: SocketAddr) -> std::io::Result<tokio::net::TcpListener> {
+    let socket = socket2::Socket::new(
+        socket2::Domain::IPV6,
+        socket2::Type::STREAM,
+        Some(socket2::Protocol::TCP),
+    )?;
+    socket.set_only_v6(true)?;
+    socket.set_reuse_address(true)?;
+    socket.set_nonblocking(true)?;
+    socket.bind(&addr.into())?;
+    socket.listen(1024)?;
+    tokio::net::TcpListener::from_std(socket.into())
+}
+
 /// 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