fix(companion): pairing QR advertises the LAN address, never a tailnet IP

The QR mirrored the browser origin — an operator browsing over Tailscale
handed the phone a 100.x address it has no route to, so pairing silently
never connected (reported 2026-07-22; the 'random password' alongside it
was the device token working as designed). system.get-hostname now also
returns the default-route LAN IPv4; the QR substitutes it (or the mDNS
name) whenever the origin is localhost or a CGNAT/tailnet 100.64/10 IP.

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

core/archipelago/src/api/rpc/system/handlers.rs

@@ -139,9 +139,17 @@ impl RpcHandler {
             .await
             .map(|s| s.trim().to_string())
             .unwrap_or_else(|_| "archipelago".to_string());
+        // LAN IPv4 rides along for the companion pairing QR: when the
+        // operator's browser reaches this node over Tailscale/VPN or
+        // localhost, that origin is useless to a phone on the LAN — the QR
+        // must advertise an address the phone can actually dial
+        // (2026-07-22: a pairing QR carried a tailnet 100.x IP and the
+        // companion could never connect).
+        let lan_ip = crate::host_ip::primary_host_ipv4().await;
         Ok(serde_json::json!({
             "hostname": hostname,
             "mdns_hostname": format!("{hostname}.local"),
+            "lan_ip": lan_ip,
         }))
     }
 

neode-ui/src/components/CompanionIntroOverlay.vue

@@ -252,21 +252,39 @@ watch(visible, async (isVisible) => {
   })
 }, { immediate: true, flush: 'post' })
 
+/** Tailscale/CGNAT range 100.64.0.0/10 — reachable only inside the tailnet. */
+function isTailnetIp(host: string): boolean {
+  const m = host.match(/^100\.(\d{1,3})\.\d{1,3}\.\d{1,3}$/)
+  return !!m && Number(m[1]) >= 64 && Number(m[1]) <= 127
+}
+
 /**
  * The server URL the companion app should connect to. The demo advertises its
- * public https origin; a real node advertises whatever address the browser is
+ * public https origin; a real node advertises the browser's own origin ONLY
- * already using — except on the kiosk, where that is localhost and useless to
+ * when a phone could plausibly reach it too. Two origins that a phone on the
- * a phone, so fall back to the node's mDNS .local name.
+ * LAN can never dial get substituted with the node's real LAN address:
+ *   - localhost/127.0.0.1 (the kiosk browses itself)
+ *   - a tailnet 100.x address (operator browsing over Tailscale — a scanned
+ *     QR carried one of these on 2026-07-22 and the companion sat there
+ *     dialing an IP the phone had no route to)
  */
 async function resolveServerUrl(): Promise<string> {
   if (IS_DEMO) return DEMO_SERVER_URL
   const { hostname, origin } = window.location
-  if (hostname !== 'localhost' && hostname !== '127.0.0.1') return origin
+  const phoneUnreachable =
+    hostname === 'localhost' || hostname === '127.0.0.1' || isTailnetIp(hostname)
+  if (!phoneUnreachable) return origin
   try {
-    const res = await rpcClient.call<{ mdns_hostname?: string }>({ method: 'system.get-hostname' })
+    const res = await rpcClient.call<{ mdns_hostname?: string; lan_ip?: string | null }>({
+      method: 'system.get-hostname',
+    })
+    // Prefer the LAN IP (phones resolve it without mDNS support — Android
+    // notoriously lacks .local); fall back to the mDNS name.
+    if (res?.lan_ip) return `http://${res.lan_ip}`
     if (res?.mdns_hostname) return `http://${res.mdns_hostname}`
   } catch {
-    // RPC unavailable — fall through to the (localhost) origin
+    // RPC unavailable — fall through to the (unreachable) origin; the app
+    // still lets the user edit the address by hand.
   }
   return origin
 }