refactor(infra): share isTailnetIPv4 helper

src/infra/bonjour-discovery.ts

@@ -1,4 +1,5 @@
 import { runCommandWithTimeout } from "../process/exec.js";
+import { isTailnetIPv4 } from "./tailnet.js";
 import { resolveWideAreaDiscoveryDomain } from "./widearea-dns.js";
 
 export type GatewayBonjourBeacon = {
@@ -70,20 +71,6 @@ function decodeDnsSdEscapes(value: string): string {
   return Buffer.from(bytes).toString("utf8");
 }
 
-function isTailnetIPv4(address: string): boolean {
-  const parts = address.split(".");
-  if (parts.length !== 4) {
-    return false;
-  }
-  const octets = parts.map((p) => Number.parseInt(p, 10));
-  if (octets.some((n) => !Number.isFinite(n) || n < 0 || n > 255)) {
-    return false;
-  }
-  // Tailscale IPv4 range: 100.64.0.0/10
-  const [a, b] = octets;
-  return a === 100 && b >= 64 && b <= 127;
-}
-
 function parseDigShortLines(stdout: string): string[] {
   return stdout
     .split("\n")

src/infra/tailnet.ts

@@ -5,7 +5,7 @@ export type TailnetAddresses = {
   ipv6: string[];
 };
 
-function isTailnetIPv4(address: string): boolean {
+export function isTailnetIPv4(address: string): boolean {
   const parts = address.split(".");
   if (parts.length !== 4) {
     return false;