Bound the prerendered archive window

Prerendering every past answer page in six languages meant 700 static pages,
and the CI runner blew past Next's 60s per-page export timeout on
/puzzle/236, failing the build. The set also grew by six pages a day, so
every build would have been slower than the last.

generateStaticParams now covers the most recent 30 days per locale (202
pages, ~35s locally). Older days keep working exactly as before: they are
still linked, still in the sitemap and still indexable, but render on first
request and are then cached by ISR — measured at 180ms cold.

Also raises staticPageGenerationTimeout to 180s for headroom, since the
runner shares a host with Gitea and Postgres.

Refs #6

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QvQ1ErZNRUcWgCEkJ9uyrn

app/(en)/puzzle/[number]/page.tsx

@@ -2,7 +2,7 @@ import type { Metadata } from "next";
 import { notFound } from "next/navigation";
 import PuzzleAnswers from "@/components/PuzzleAnswers";
 import { ARCHIVE_COPY } from "@/lib/archive-content";
-import { getArchiveDateKeys, getPastPuzzleSet, getPuzzleNumber, getTodayKey } from "@/lib/game-engine";
+import { getPastPuzzleSet, getPuzzleNumber, getRecentArchiveDateKeys, getTodayKey } from "@/lib/game-engine";
 import { BASE_URL, puzzleHreflang, puzzlePath } from "@/lib/seo-content";
 
 export const revalidate = 3600;
@@ -11,11 +11,11 @@ type PuzzlePageProps = {
   params: Promise<{ number: string }>;
 };
 
-// Past answers never change, so every one of them is prerendered. Days that roll
-// over after the build are still served: dynamicParams stays on by default and
-// they get rendered (and cached) on first request.
+// Only the recent window is prerendered (see PRERENDERED_ARCHIVE_DAYS). Older
+// days and days that roll over after the build are still served: dynamicParams
+// stays on by default, so they render on first request and are then cached.
 export function generateStaticParams() {
-  return getArchiveDateKeys(getTodayKey()).map((dateKey) => ({
+  return getRecentArchiveDateKeys(getTodayKey()).map((dateKey) => ({
     number: String(getPuzzleNumber(dateKey)),
   }));
 }

app/(intl)/[locale]/puzzle/[number]/page.tsx

@@ -2,7 +2,7 @@ import type { Metadata } from "next";
 import { notFound } from "next/navigation";
 import PuzzleAnswers from "@/components/PuzzleAnswers";
 import { ARCHIVE_COPY } from "@/lib/archive-content";
-import { getArchiveDateKeys, getPastPuzzleSet, getPuzzleNumber, getTodayKey } from "@/lib/game-engine";
+import { getPastPuzzleSet, getPuzzleNumber, getRecentArchiveDateKeys, getTodayKey } from "@/lib/game-engine";
 import { BASE_URL, INTL_LOCALES, puzzleHreflang, puzzlePath } from "@/lib/seo-content";
 import { resolveIntlLocale } from "@/lib/intl-route";
 
@@ -12,10 +12,10 @@ type LocalePuzzleProps = {
   params: Promise<{ locale: string; number: string }>;
 };
 
-// 5 locales x every past day. They are tiny data-only pages, and prerendering
-// them is what makes the localized long tail crawlable without a cold render.
+// 5 locales x the recent window (see PRERENDERED_ARCHIVE_DAYS). The whole
+// archive is still crawlable — the rest is rendered on demand and cached.
 export function generateStaticParams() {
-  const numbers = getArchiveDateKeys(getTodayKey()).map((dateKey) => String(getPuzzleNumber(dateKey)));
+  const numbers = getRecentArchiveDateKeys(getTodayKey()).map((dateKey) => String(getPuzzleNumber(dateKey)));
   return INTL_LOCALES.flatMap((locale) => numbers.map((number) => ({ locale, number })));
 }
 

lib/game-engine.ts

@@ -55,6 +55,17 @@ export function getPastPuzzleSet(rawNumber: string): { number: number; dateKey:
   return { number, dateKey, sets };
 }
 
+// How many recent days get prerendered at build time. The archive grows by one
+// day forever, so an unbounded generateStaticParams would make every CI build
+// slower than the last — 700 pages already blew past Next's per-page export
+// timeout. Older answer pages stay fully public and indexable: they are just
+// rendered on first request and then cached by ISR.
+export const PRERENDERED_ARCHIVE_DAYS = 30;
+
+export function getRecentArchiveDateKeys(todayKey: string): string[] {
+  return getArchiveDateKeys(todayKey).slice(0, PRERENDERED_ARCHIVE_DAYS);
+}
+
 export function getDailyPuzzles(dateKey: string): Puzzle[] {
   const dated = puzzles.filter((puzzle) => puzzle.date === dateKey);
   const source = dated.length === DIFFICULTIES.length ? dated : getRotatingPuzzleSet(dateKey);

next.config.js

@@ -2,6 +2,9 @@
 const nextConfig = {
   htmlLimitedBots: /.*/,
   output: "standalone",
+  // The CI runner shares a host with other services, so a cold page render can
+  // occasionally crawl. 60s (the default) was not enough headroom.
+  staticPageGenerationTimeout: 180,
 };
 
 module.exports = nextConfig;