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/bandcamp-streams.ts

@@ -9,19 +9,16 @@
  */
 
 import { APIException } from "../lib/api-exception.ts";
+import { TtlCache } from "../lib/ttl-cache.ts";
 import { fetchWithTimeout, isValidHttpUrl, readTextCapped } from "./fetch.ts";
 import { BANDCAMP_HOST_RE, parseTralbum } from "./bandcamp-tralbum.ts";
 import type { Tralbum } from "../../shared/player.ts";
 
 /**
- * Half the signatures' life, so a cached URL still has at least 12 hours left
- * when it is handed out.
+ * Lives half the signatures' life, so a cached URL still has at least 12
+ * hours left when it is handed out.
  */
-const TTL_MS = 12 * 60 * 60 * 1000;
-/** The oldest write goes first. */
-const MAX_ENTRIES = 200;
-
-const cache = new Map<string, Tralbum>();
+const cache = new TtlCache<Tralbum>(12 * 3_600_000, 200);
 
 /**
  * Returns `url` without its query, fragment and trailing slashes, and with its
@@ -38,25 +35,6 @@ function cacheKey(url: string): string {
   }
 }
 
-function readCache(key: string): Tralbum | null {
-  const hit = cache.get(key);
-  if (!hit) return null;
-  if (Date.now() - hit.resolvedAt > TTL_MS) {
-    cache.delete(key);
-    return null;
-  }
-  return hit;
-}
-
-function writeCache(key: string, value: Tralbum): void {
-  // Map preserves insertion order, so the first key is the oldest write.
-  if (cache.size >= MAX_ENTRIES) {
-    const oldest = cache.keys().next().value;
-    if (oldest !== undefined) cache.delete(oldest);
-  }
-  cache.set(key, value);
-}
-
 /**
  * Returns the tracklist of the Bandcamp page `pageUrl`, from the cache when it
  * was resolved in the last 12 hours. `force` skips the cache: the player sets
@@ -87,7 +65,7 @@ export async function resolveBandcamp(
 
   const key = cacheKey(pageUrl);
   if (!force) {
-    const hit = readCache(key);
+    const hit = cache.get(key);
     if (hit) return hit;
   }
 
@@ -115,6 +93,5 @@ export async function resolveBandcamp(
     throw new APIException(404, "No streamable tracks on this page");
   }
 
-  writeCache(key, parsed);
-  return parsed;
+  return cache.set(key, parsed);
 }