fix: treat tailnet host as local for pairing

src/gateway/net.test.ts

@@ -0,0 +1,41 @@
+import { beforeEach, describe, expect, test, vi } from "vitest";
+
+const testTailnetIPv4 = { value: undefined as string | undefined };
+const testTailnetIPv6 = { value: undefined as string | undefined };
+
+vi.mock("../infra/tailnet.js", () => ({
+  pickPrimaryTailnetIPv4: () => testTailnetIPv4.value,
+  pickPrimaryTailnetIPv6: () => testTailnetIPv6.value,
+}));
+
+import { isLocalGatewayAddress } from "./net.js";
+
+describe("gateway net", () => {
+  beforeEach(() => {
+    testTailnetIPv4.value = undefined;
+    testTailnetIPv6.value = undefined;
+  });
+
+  test("treats loopback as local", () => {
+    expect(isLocalGatewayAddress("127.0.0.1")).toBe(true);
+    expect(isLocalGatewayAddress("127.0.1.1")).toBe(true);
+    expect(isLocalGatewayAddress("::1")).toBe(true);
+    expect(isLocalGatewayAddress("::ffff:127.0.0.1")).toBe(true);
+  });
+
+  test("treats local tailnet IPv4 as local", () => {
+    testTailnetIPv4.value = "100.64.0.1";
+    expect(isLocalGatewayAddress("100.64.0.1")).toBe(true);
+    expect(isLocalGatewayAddress("::ffff:100.64.0.1")).toBe(true);
+  });
+
+  test("ignores non-matching tailnet IPv4", () => {
+    testTailnetIPv4.value = "100.64.0.1";
+    expect(isLocalGatewayAddress("100.64.0.2")).toBe(false);
+  });
+
+  test("treats local tailnet IPv6 as local", () => {
+    testTailnetIPv6.value = "fd7a:115c:a1e0::123";
+    expect(isLocalGatewayAddress("fd7a:115c:a1e0::123")).toBe(true);
+  });
+});