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/services/rich-content-service.ts

@@ -8,6 +8,8 @@
  */
 
 import type { RichContent } from "../../shared/dump.ts";
+import { siteHost } from "../../shared/url.ts";
+import { TtlCache } from "../lib/ttl-cache.ts";
 import type { RichContentProvider } from "../remote/providers/provider.ts";
 import { youtubeProvider } from "../remote/providers/youtube.ts";
 import { bandcampProvider } from "../remote/providers/bandcamp.ts";
@@ -47,19 +49,12 @@ export interface FetchRichContentResult {
   content?: RichContent;
 }
 
-/** How long a fetched preview is reused. */
-const RECENT_TTL_MS = 5 * 60 * 1000;
-/** How many previews are kept. The oldest written goes first. */
-const RECENT_MAX = 200;
 /**
  * Makes posting a link fast after the create form previewed it, by keeping the
- * previews fetched in the last few minutes, by URL. Without it, the second
+ * previews fetched in the last five minutes, by URL. Without it, the second
  * fetch of the page was the slow part of posting. Only successes are kept.
  */
-const recent = new Map<
-  string,
-  { at: number; result: Promise<FetchRichContentResult> }
->();
+const recent = new TtlCache<Promise<FetchRichContentResult>>(5 * 60_000, 200);
 
 /**
  * Forgets every cached preview. The tests' `stubNetwork` calls it, since
@@ -78,20 +73,13 @@ export function tryFetchRichContent(
   url: string,
   { fresh = false }: { fresh?: boolean } = {},
 ): Promise<FetchRichContentResult> {
-  const hit = recent.get(url);
-  if (!fresh && hit && Date.now() - hit.at < RECENT_TTL_MS) return hit.result;
-  recent.delete(url);
+  const hit = fresh ? undefined : recent.get(url);
+  if (hit) return hit;
 
   // Stored while in flight too, so a preview and a post racing share a fetch.
-  const result = fetchRichContentUncached(url);
-  if (recent.size >= RECENT_MAX) {
-    const oldest = recent.keys().next().value;
-    if (oldest !== undefined) recent.delete(oldest);
-  }
-  const entry = { at: Date.now(), result };
-  recent.set(url, entry);
+  const result = recent.set(url, fetchRichContentUncached(url));
   result.then(({ ok }) => {
-    if (!ok && recent.get(url) === entry) recent.delete(url);
+    if (!ok) recent.delete(url, result);
   });
   return result;
 }
@@ -108,18 +96,10 @@ async function fetchRichContentUncached(
     return { ok: true, content: await provider.fetch(url) };
   } catch (err) {
     console.error(`[rich-content] Failed to fetch metadata for ${url}:`, err);
-    try {
-      return {
-        ok: false,
-        content: {
-          type: "generic",
-          url,
-          siteName: new URL(url).hostname.replace(/^www\./, ""),
-        },
-      };
-    } catch {
-      return { ok: false };
-    }
+    const siteName = siteHost(url);
+    return siteName
+      ? { ok: false, content: { type: "generic", url, siteName } }
+      : { ok: false };
   }
 }