v4: what the server and the client both state is declared once — several rules were written out in two or more files, some already drifting apart. A link's site name (its host without www.) was computed in five places, now shared/url.ts's siteHost; dumpFileVersion, which the frontend and the server had to keep equal by hand, is one function in shared/dump.ts; the Markdown flattening of the chat's reply previews and the digest's quotes is shared/markdown.ts's markdownToPlainText, so the digest also keeps an image's alt text; an attachment's URL and how to find one in a text are shared/attachment.ts, which the editor, Markdown and attachment-service read, its id pattern the new UUID_RE that the file and thumbnail routes check ids with. On the server, the Bandcamp, YouTube playlist and link preview caches use one TtlCache (api/lib/ttl-cache.ts) instead of three copies of the same expiry and eviction; the link previews' theme-color and the emails' theme tokens read colours with one parser (api/lib/css-color.ts), and a transparent theme-color now gives no tint; the WebSocket route sends through ws-service's send, the welcome included, so it is type-checked; fetch.ts strips an IPv6 literal's brackets with public-address's bareHostname; and a category's slug is checked by the same validateSlug as a dump's, with its own length. The migrations keep their frozen copies, as they document. 272 backend tests and 677 frontend tests pass, and deno check, tsc, eslint and doc:lint are clean.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

api/lib/slugify.ts

@@ -72,14 +72,15 @@ export function uniqueSlug(
 
 /**
  * Throws a 400 unless `slug` is a valid slug, lowercase words of letters and
- * digits joined by hyphens, at most `SLUG_MAX` long. Dump and playlist slugs
- * reserve no word: nothing else a user names lives beside them.
+ * digits joined by hyphens, at most `max` long. slug-service checks a dump's
+ * or a playlist's with it, and category-service a category's, with that
+ * kind's own limit.
  */
-export function validateSlug(slug: string): void {
-  if (!isValidSlug(slug)) {
+export function validateSlug(slug: string, max: number = SLUG_MAX): void {
+  if (!isValidSlug(slug, max)) {
     throw new APIException(
       400,
-      `Slug must be lowercase letters, numbers and hyphens, at most ${SLUG_MAX} characters`,
+      `Slug must be lowercase letters, numbers and hyphens, at most ${max} characters`,
     );
   }
 }