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/routes/files.ts

@@ -16,18 +16,15 @@
 import { Router } from "@oak/oak";
 import { APIException } from "../lib/api-exception.ts";
 import type { APIResponse } from "../../shared/api.ts";
-import type { Dump } from "../../shared/dump.ts";
+import { type Dump, dumpFileVersion } from "../../shared/dump.ts";
 import { DUMPS_DIR } from "../config.ts";
+import { UUID_RE } from "../../shared/validation.ts";
 import { authenticateMedia } from "../lib/auth.ts";
 import { can } from "../lib/permissions.ts";
 import { serveFile } from "../lib/serve-file.ts";
 import { authMiddleware } from "../middleware/auth.ts";
 import { parseCategoryIds } from "../validators/dump.ts";
-import {
-  dumpFileVersion,
-  getDump,
-  replaceFileDump,
-} from "../services/dump-service.ts";
+import { getDump, replaceFileDump } from "../services/dump-service.ts";
 
 /**
  * Mounted by `api/main.ts` behind the error, Open Graph and CORS middleware.
@@ -71,7 +68,7 @@ router.get("/:dumpId/file", async (ctx) => {
   const { dumpId } = ctx.params;
 
   // The id names a file on disk: nothing but an id's characters gets through.
-  if (!/^[0-9a-f-]{36}$/.test(dumpId)) {
+  if (!UUID_RE.test(dumpId)) {
     throw new APIException(400, "Invalid dump ID");
   }