fix(config): reject malformed domain labels

lib/config.ts

@@ -133,6 +133,8 @@ export function safeDomain(dn: unknown): string | null {
     .replace(/^https?:\/\//, "")
     .replace(/[/?#&].*$/, "");
   if (!/^[a-z0-9.-]{3,253}$/.test(d) || !d.includes(".") || d.includes("..")) return null;
+  if (d.startsWith(".") || d.endsWith(".")) return null;
+  if (d.split(".").some((label) => label.startsWith("-") || label.endsWith("-"))) return null;
   return d;
 }
 

tests/safe-domain.test.mjs

@@ -0,0 +1,19 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+
+import { safeDomain } from "../lib/config.ts";
+
+test("safeDomain strips forwarded paths and accepts ordinary domains", () => {
+  assert.equal(safeDomain("https://example.com/path?ref=abc"), "example.com");
+  assert.equal(safeDomain("Sub.Example.COM#top"), "sub.example.com");
+});
+
+test("safeDomain rejects empty labels and edge punctuation", () => {
+  assert.equal(safeDomain(".example.com"), null);
+  assert.equal(safeDomain("example.com."), null);
+  assert.equal(safeDomain("example..com"), null);
+  assert.equal(safeDomain("-example.com"), null);
+  assert.equal(safeDomain("example-.com"), null);
+  assert.equal(safeDomain("example.-com"), null);
+  assert.equal(safeDomain("example.com-"), null);
+});