feat(client): refresh TAP IP diagnostics

The Windows client sampled TAP diagnostics once when opening the adapter. That
can miss the useful DHCP result because the TAP interface may not receive a LAN
address until after frame bridging starts.

Keep the stable TAP diagnostics fields from startup, but retain the interface
identity and re-read the TAP unicast IP whenever the periodic diagnostics tick
prints and reports a snapshot. Later status lines can now show the DHCP address
that arrives after the tunnel is already moving traffic.

Test Plan:
- cargo fmt --check
- cargo test -p lanparty-client-win
- cargo test --workspace
- cargo clippy --workspace --all-targets -- -D warnings
- git diff --check

Refs: PLAN.md

crates/lanparty-client-win/src/main.rs

@@ -1,6 +1,9 @@
-#[cfg(windows)]
-use std::net::IpAddr;
-use std::{collections::BTreeMap, fs, net::SocketAddr, path::PathBuf};
+use std::{
+    collections::BTreeMap,
+    fs,
+    net::{IpAddr, SocketAddr},
+    path::PathBuf,
+};
 #[cfg(windows)]
 use std::{
     sync::{Arc, mpsc},
@@ -139,6 +142,7 @@ async fn run_client(session: &ClientSession, relay_route_pin: &PinnedRelayRoute)
     let OpenedTapAdapter {
         tap,
         tap_diagnostics,
+        tap_interface,
         _route_guard,
     } = open_tap_adapter(session)?;
     let relay_route =
@@ -147,7 +151,11 @@ async fn run_client(session: &ClientSession, relay_route_pin: &PinnedRelayRoute)
     print_verified_relay_route(&relay_route);
     print_and_report_client_diagnostics(
         session,
-        &client_diagnostics_snapshot(session, true, tap_diagnostics.clone()),
+        &client_diagnostics_snapshot(
+            session,
+            true,
+            current_tap_diagnostics(&tap_diagnostics, tap_interface),
+        ),
     )
     .await;
     println!(
@@ -186,7 +194,11 @@ async fn run_client(session: &ClientSession, relay_route_pin: &PinnedRelayRoute)
             _ = diagnostics_check.tick() => {
                 print_and_report_client_diagnostics(
                     session,
-                    &client_diagnostics_snapshot(session, true, tap_diagnostics.clone()),
+                    &client_diagnostics_snapshot(
+                        session,
+                        true,
+                        current_tap_diagnostics(&tap_diagnostics, tap_interface),
+                    ),
                 ).await;
             }
         }
@@ -313,6 +325,7 @@ fn route_next_hop_label(next_hop: Option<std::net::IpAddr>) -> String {
 struct OpenedTapAdapter {
     tap: TapAdapter,
     tap_diagnostics: TapDiagnostics,
+    tap_interface: NetworkInterfaceIdentity,
     _route_guard: TapRouteProtectionGuard,
 }
 
@@ -353,17 +366,17 @@ fn open_tap_adapter(session: &ClientSession) -> Result<OpenedTapAdapter> {
         tap_interface.index(),
         tap_interface.luid()
     );
-    let tap_ip = tap_unicast_ip(tap_interface);
     let tap_diagnostics = TapDiagnostics::new(
         true,
         Some(driver_mac),
         Some(session.welcome().effective_tap_mtu()),
-        tap_ip,
+        None,
     );
 
     Ok(OpenedTapAdapter {
         tap,
         tap_diagnostics,
+        tap_interface,
         _route_guard: route_guard,
     })
 }
@@ -398,6 +411,19 @@ fn client_diagnostics_snapshot(
     )
 }
 
+#[cfg(windows)]
+fn current_tap_diagnostics(
+    base: &TapDiagnostics,
+    identity: NetworkInterfaceIdentity,
+) -> TapDiagnostics {
+    tap_diagnostics_with_ip(base, tap_unicast_ip(identity))
+}
+
+#[cfg_attr(not(windows), allow(dead_code))]
+fn tap_diagnostics_with_ip(base: &TapDiagnostics, ip: Option<IpAddr>) -> TapDiagnostics {
+    TapDiagnostics::new(base.adapter_found(), base.mac(), base.mtu(), ip)
+}
+
 fn print_client_diagnostics(diagnostics: &ClientDiagnostics) {
     println!("{}", format_client_diagnostics(diagnostics));
 }
@@ -801,6 +827,24 @@ mod tests {
         );
     }
 
+    #[test]
+    fn refreshes_tap_diagnostics_ip_without_losing_static_fields() {
+        let base = TapDiagnostics::new(
+            true,
+            Some(mac(1)),
+            Some(1200),
+            Some("169.254.10.20".parse().unwrap()),
+        );
+
+        let refreshed =
+            tap_diagnostics_with_ip(&base, Some("10.73.42.51".parse::<IpAddr>().unwrap()));
+
+        assert!(refreshed.adapter_found());
+        assert_eq!(refreshed.mac(), Some(mac(1)));
+        assert_eq!(refreshed.mtu(), Some(1200));
+        assert_eq!(refreshed.ip().unwrap().to_string(), "10.73.42.51");
+    }
+
     #[test]
     fn formats_relay_lifecycle_events() {
         let gateway = ControlMessage::PeerJoined(PeerInfo::new(1, Role::Gateway, None).unwrap());