fix(e2e): resolve WANHost from spinifex.toml advertise on single-node (#527)

discoverSingleNodeIPs seeds 127.0.0.1 then appends net.InterfaceAddrs()
in undefined order, so WANHost=nodeIPs[0] was loopback and the guest
gateway URL helpers fell through to the first non-loopback interface
addr — an arbitrary co-tenant bridge on multi-bridge shared hosts
(wattle: br-lan-env1..23, br-wan), leaving guest VMs unable to reach the
advertised gateway to register.

Resolve WANHost from spinifex.toml nodes.<node>.advertise (falling back
to that node's host), mirroring awsgwBindIP's toml scan; fall back to the
first non-loopback discovered addr only when config is unreadable. This
removes the need for the SPINIFEX_WAN_IP override on shared hosts.

tests/e2e/harness/env.go

@@ -81,6 +81,20 @@ func LoadEnv(t *testing.T) *Env {
 	}
 
 	wanHost := getenv("SPINIFEX_WAN_IP", "")
+	if wanHost == "" && mode == ModeSingle {
+		// Prefer the node's advertised address so multi-bridge shared hosts
+		// resolve the advertised WAN bridge, not an arbitrary co-tenant bridge
+		// picked by interface-enumeration order.
+		wanHost = advertiseIP(configDir)
+	}
+	if wanHost == "" {
+		for _, ip := range nodeIPs {
+			if !strings.HasPrefix(ip, "127.") {
+				wanHost = ip
+				break
+			}
+		}
+	}
 	if wanHost == "" && len(nodeIPs) > 0 {
 		wanHost = nodeIPs[0]
 	}
@@ -196,3 +210,54 @@ func awsgwBindIP(configDir string) string {
 	}
 	return ""
 }
+
+var (
+	tomlNodeLine      = regexp.MustCompile(`(?i)^\s*node\s*=\s*"([^"]+)"`)
+	tomlAdvertiseLine = regexp.MustCompile(`(?i)^\s*advertise\s*=\s*"([^":]+)`)
+	tomlHostLine      = regexp.MustCompile(`(?i)^\s*host\s*=\s*"([^":]+)`)
+)
+
+// advertiseIP returns the externally-reachable address of the local node from
+// spinifex.toml (nodes.<node>.advertise, or that node's host when advertise is
+// unset). The local node is named by the top-level node key. Returns "" when
+// the file or node cannot be resolved so callers fall back to interface scan.
+func advertiseIP(configDir string) string {
+	if configDir == "" {
+		return ""
+	}
+	f, err := os.Open(filepath.Join(configDir, "spinifex.toml"))
+	if err != nil {
+		return ""
+	}
+	defer f.Close()
+
+	var node, advertise, host string
+	inNode := false
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		line := strings.TrimSpace(scanner.Text())
+		if strings.HasPrefix(line, "[") {
+			// Match only the [nodes.<node>] top-level table, not sub-tables
+			// like [nodes.<node>.awsgw].
+			inNode = node != "" && line == "[nodes."+node+"]"
+			continue
+		}
+		if !inNode {
+			if node == "" {
+				if m := tomlNodeLine.FindStringSubmatch(line); m != nil {
+					node = m[1]
+				}
+			}
+			continue
+		}
+		if m := tomlAdvertiseLine.FindStringSubmatch(line); m != nil {
+			advertise = m[1]
+		} else if m := tomlHostLine.FindStringSubmatch(line); m != nil {
+			host = m[1]
+		}
+	}
+	if advertise != "" {
+		return advertise
+	}
+	return host
+}

tests/e2e/harness/wanhost_test.go

@@ -0,0 +1,76 @@
+//go:build e2e
+
+package harness
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestAdvertiseIP(t *testing.T) {
+	cases := []struct {
+		name string
+		toml string
+		want string
+	}{
+		{
+			name: "advertise preferred over host and ignores sub-tables",
+			toml: `node = "wattle"
+[nodes.wattle]
+host = "10.105.1.3"
+advertise = "192.168.1.13"
+[nodes.wattle.awsgw]
+host = "10.105.1.3:9999"
+`,
+			want: "192.168.1.13",
+		},
+		{
+			name: "falls back to host when advertise unset",
+			toml: `node = "dev1"
+[nodes.dev1]
+host = "192.168.1.20"
+`,
+			want: "192.168.1.20",
+		},
+		{
+			name: "resolves only the local node, not co-tenant nodes",
+			toml: `node = "n2"
+[nodes.n1]
+host = "10.0.0.1"
+advertise = "1.1.1.1"
+[nodes.n2]
+host = "10.0.0.2"
+advertise = "2.2.2.2"
+`,
+			want: "2.2.2.2",
+		},
+		{
+			name: "empty when top-level node key is absent",
+			toml: `[nodes.x]
+advertise = "9.9.9.9"
+`,
+			want: "",
+		},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			dir := t.TempDir()
+			if err := os.WriteFile(filepath.Join(dir, "spinifex.toml"), []byte(tc.toml), 0o600); err != nil {
+				t.Fatalf("write toml: %v", err)
+			}
+			if got := advertiseIP(dir); got != tc.want {
+				t.Fatalf("advertiseIP = %q, want %q", got, tc.want)
+			}
+		})
+	}
+}
+
+func TestAdvertiseIPMissing(t *testing.T) {
+	if got := advertiseIP(""); got != "" {
+		t.Fatalf("advertiseIP(\"\") = %q, want empty", got)
+	}
+	if got := advertiseIP(t.TempDir()); got != "" {
+		t.Fatalf("advertiseIP(missing file) = %q, want empty", got)
+	}
+}