```javascript
// article.mjs
//
// Fourth pass. Standing note, unchanged: zod ships no string-to-slug transform
// (no `z.slug()`, no `z.string().slug()`, no `.toSlug()` in v3 or v4), so this
// file cannot literally defer to one. What it does instead is be the single
// implementation that the API and the web client both import, which is what
// actually makes the two sides agree character for character.
//
// Convention implemented, now reconciled with all three reported expectations:
//   1. Lowercase.
//   2. Treat whitespace, "_" and "-" as SEPARATORS.
//   3. DELETE every other character that is not [a-z0-9] — accented letters,
//      non-Latin scripts, punctuation and emoji are dropped outright, not
//      folded to an ASCII base and not turned into separators.
//   4. Collapse every run of separators into a single "-".
//   5. Trim leading and trailing "-".
//
//   "Hello, World!"     -> "hello-world"
//   "Héllo Wörld"       -> "hllo-wrld"
//   "under_score_case"  -> "under-score-case"
//   "a -- b"            -> "a-b"
//   "Ship it 🚀🚀"       -> "ship-it"

import { z } from "zod";

/** Convert arbitrary text into a URL slug. Single source of truth. */
export function slugify(input) {
  return input
    .toLowerCase()
    .replace(/[^a-z0-9\s_-]+/g, "")
    .replace(/[\s_-]+/g, "-")
    .replace(/^-+|-+$/g, "");
}

/**
 * Accepts a string, produces its slug.
 * Slug.parse("Hello, World!")    === "hello-world"
 * Slug.parse("Héllo Wörld")      === "hllo-wrld"
 * Slug.parse("under_score_case") === "under-score-case"
 */
export const Slug = z.string().transform(slugify);

/**
 * Article.parse({ title: "Hello, World!", slug: "Hello, World!" })
 *   === { title: "Hello, World!", slug: "hello-world" }
 */
export const Article = z.object({
  title: z.string().min(3),
  slug: Slug,
});
```

TOOLS_USED: none