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/remote/providers/generic.ts

@@ -7,6 +7,7 @@
 
 import type { RichContent } from "../../../shared/dump.ts";
 import type { RichContentProvider } from "./provider.ts";
+import { siteHost } from "../../../shared/url.ts";
 import {
   extractBestIcon,
   extractFirstContentImage,
@@ -66,7 +67,7 @@ export const genericProvider: RichContentProvider = {
       extractPageTitle(html);
 
     const siteName = extractOgTag(html, "site_name") ??
-      new URL(url).hostname.replace(/^www\./, "");
+      siteHost(url);
 
     const description = extractOgTag(html, "description") ??
       extractMetaName(html, "twitter:description") ??

api/remote/providers/youtube.ts

@@ -11,12 +11,13 @@ import type { RichContentProvider } from "./provider.ts";
 import { extractOgTag } from "../html.ts";
 import { fetchWithTimeout, readTextCapped } from "../fetch.ts";
 import { youtubeHost, youtubeVideoId } from "../../lib/canonical-url.ts";
+import { siteHostOf } from "../../../shared/url.ts";
 
 /** Returns the id of the video `url` points at, in any shape YouTube uses. */
 function extractVideoId(url: string): string | null {
   try {
     const u = new URL(url);
-    const host = u.hostname.toLowerCase().replace(/^www\./, "");
+    const host = siteHostOf(u);
     return youtubeVideoId(host, u.pathname, u.searchParams);
   } catch {
     return null;