v3: comments say what the code can't — the documentation pass wanted JSDoc on every export and every field of an exported interface, which filled the code with restatements ("The dump.", "Whether it is loading.", "The props of X.", "Renders the X.") and module docs that told a reader nothing ("The hot and new feeds, and the props every main feed of the index takes."); some were wrong as well as vague. Every comment in api/, shared/ and src/ is rewritten under one rule, now stated in the README's "Comments" section: every module and export still has a JSDoc, and it gives context (who uses it and where), usage (what a caller must know: a precondition, what it leaves to the caller, a side effect) or its place in the chain (where its input comes from, where its output goes); a field, parameter, private function or local gets one only when it adds to its parent's, and context about a whole type goes on the type; a type's doc is phrased from the value's side ("Returned to Y by X when Z", "Passed to Y by X"); full sentences, as short as they can be, no label-colon-list; // goes wherever the code isn't obvious and says why, and the section banners and narration go. Every claim was checked against the code, which turned up some forty comments that were wrong: DumpCard's claimed it was only used by the hot and new feeds, the WebSocket welcome claimed to be a socket's first message (presence comes first), UpdateUserRequest said null removes a description (it keeps it), deletedDumpIds leaves out that it also holds dumps made private, THEME_COLOR claimed to mirror index.html's, and the like. The routers' JSDoc now says where they are mounted and what becomes of a thrown APIException. doc-lint.ts lets a field without a doc through; a module or export without one still fails. No code changes; 204 backend and 628 frontend tests pass, and doc:lint, deno check, deno lint and tsc are clean.

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

api/routes/playlists.ts

@@ -1,11 +1,13 @@
 /**
- * The playlist routes. `:playlistId` takes an id or a slug.
+ * Serves playlists, their dumps and their covers. `:playlistId` takes an id or
+ * a slug.
  *
  * - `GET /api/playlists/by-dump/:dumpId/memberships` — signed in. Answers each
  *   of the caller's playlists and whether it holds the dump.
  * - `POST /api/playlists` — signed in. Creates a playlist.
  * - `GET /api/playlists/:playlistId` — optional sign-in. Answers a playlist
- *   with the dumps the caller may see in it; a private one only to its owner.
+ *   with the dumps the caller may see in it. A private one 404s but for its
+ *   owner.
  * - `PUT /api/playlists/:playlistId` — signed in, as its owner or with
  *   `playlist:moderate`. Updates its title, description and visibility.
  * - `DELETE /api/playlists/:playlistId` — signed in, as its owner or with
@@ -16,8 +18,8 @@
  *   or with `playlist:moderate`. Removes a dump.
  * - `POST /api/playlists/:playlistId/image` — signed in, as its owner or with
  *   `playlist:moderate`. Replaces its cover (multipart `file`, at most 5 MB).
- * - `GET /api/playlists/:playlistId/image?token=` — public; a private
- *   playlist's cover needs its owner's media `token`. Serves its cover; 404
+ * - `GET /api/playlists/:playlistId/image?token=` — public, but a private
+ *   playlist's cover needs its owner's media `token`. Serves its cover, or 404s
  *   without one.
  * - `PUT /api/playlists/:playlistId/order` — signed in, as its owner or with
  *   `playlist:moderate`. Reorders the dumps the caller can see in it.
@@ -60,7 +62,10 @@ import {
   validateImageUpload,
 } from "../lib/upload.ts";
 
-/** The router serving the endpoints the module doc lists. */
+/**
+ * Mounted by `api/main.ts` behind the error, Open Graph and CORS middleware.
+ * An `APIException` thrown by a handler becomes the JSON error response there.
+ */
 const router: Router<AuthState> = new Router<AuthState>({
   prefix: "/api/playlists",
 });
@@ -170,11 +175,10 @@ router.post("/:playlistId/image", authMiddleware, async (ctx) => {
   const data = new Uint8Array(await file.arrayBuffer());
   const mime = validateImageUpload(data);
 
-  // The file goes in before the row changes. Setting image_mime and bumping
-  // updated_at announces the cover (the `?v=` on its URL, the socket event),
-  // so the bytes must already be there: an earlier fetch would cache the old
-  // cover under the new URL, and a failed write would leave a cover that 404s.
-  // Written beside and renamed over, so the old cover is never half-replaced.
+  // The file is written before setPlaylistImage announces it, or clients would
+  // fetch the new `?v=` URL too early and cache the old cover under it. It is
+  // written beside the old one and renamed over it, so a failed write leaves
+  // the old cover whole.
   const { id } = getEditablePlaylist(
     ctx.params.playlistId,
     ctx.state.user.userId,
@@ -210,7 +214,7 @@ router.get("/:playlistId/image", async (ctx) => {
     ctx.response.status = 404;
     return;
   }
-  // The URL may carry a media token; keep it out of anyone else's logs.
+  // The URL may carry a media token, which a Referer would leak.
   ctx.response.headers.set("Referrer-Policy", "no-referrer");
   await serveUploadedFile(
     ctx,