Pin seed->word across both languages with a shared hash

engine.ts used mulberry32 and engine.py used random.Random(seed). Same seed,
different word — so every ?seed= permalink on the site would have shown a
different puzzle than the recorded run it claimed to be replaying, and nobody
would have noticed until someone checked one by hand.

Both now derive the index from FNV-1a 32-bit over the decimal seed. A hash
rather than a PRNG because there is no honest one-line JavaScript equivalent of
Mersenne Twister, and this way there is nothing to keep in step: both sides
compute the same integer from the same string. Math.imul on the JS side is
load-bearing — a plain multiply overflows into a double and diverges after the
first few bytes.

Twelve seeds are pinned as a vector in both test suites.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019mt6sHQHEnEYrJZvoMCJSB

src/pages/NotFound.tsx

@@ -0,0 +1,101 @@
+import { Link, useLocation } from 'react-router-dom';
+import { ArrowRight } from 'lucide-react';
+
+import { allDemos, lineup, REPO_URL, routes } from '@/content/lineup';
+import * as s from '@/content/styles';
+
+/**
+ * A 404 with somewhere to go.
+ *
+ * The destinations are read from the registry and the lineup rather than
+ * hard-coded, so this page cannot become the one place on the site that still
+ * links to a demo we removed.
+ */
+export default function NotFound() {
+  const { pathname } = useLocation();
+  const topVerticals = lineup.slice(0, 4);
+
+  return (
+    <main className={`${s.shell} py-16 sm:py-24`}>
+      <p className={`${s.eyebrow} nums`}>404</p>
+      <h1 className={`${s.h1} mt-3 max-w-2xl`}>That page isn’t here.</h1>
+      <p className={`${s.lede} mt-5 max-w-2xl`}>
+        Nothing is served at{' '}
+        <code className="break-all font-mono text-fg">{pathname}</code>. Either the link is old or
+        we moved something. Here is everything this site has.
+      </p>
+
+      <div className="mt-8 flex flex-col gap-3 sm:flex-row">
+        <Link className={s.btnPrimary} to={routes.home}>
+          Start at the beginning
+        </Link>
+        <Link className={s.btnSecondary} to={routes.gallery}>
+          Every environment
+        </Link>
+      </div>
+
+      <div className="mt-12 grid gap-8 sm:grid-cols-2">
+        <nav aria-labelledby="nf-demos">
+          <h2 className={s.h3} id="nf-demos">
+            Demos
+          </h2>
+          <ul className="mt-3 space-y-2">
+            {allDemos.map((demo) => (
+              <li key={demo.slug}>
+                <Link className={`${s.link} text-sm`} to={routes.demo(demo.slug)}>
+                  {demo.title}
+                </Link>
+                <span className="ml-2 text-xs text-muted">
+                  {demo.status === 'live' ? 'Live' : 'Specification'}
+                </span>
+              </li>
+            ))}
+            {allDemos.length === 0 ? (
+              <li className="text-sm text-muted">No demos are registered yet.</li>
+            ) : null}
+          </ul>
+        </nav>
+
+        <nav aria-labelledby="nf-verticals">
+          <h2 className={s.h3} id="nf-verticals">
+            The lineup
+          </h2>
+          <ul className="mt-3 space-y-2">
+            {topVerticals.map((v) => (
+              <li key={v.slug}>
+                <Link className={`${s.link} text-sm`} to={routes.vertical(v.slug)}>
+                  {v.title}
+                </Link>
+              </li>
+            ))}
+            <li>
+              <Link
+                className="inline-flex items-center gap-1.5 text-sm font-medium text-muted transition-colors duration-1 ease-enter hover:text-fg"
+                to={routes.home}
+              >
+                All {lineup.length}
+                <ArrowRight aria-hidden="true" className="size-3.5" />
+              </Link>
+            </li>
+          </ul>
+        </nav>
+      </div>
+
+      <div className="card mt-12 p-5">
+        <h2 className={s.h3}>Looking for the numbers?</h2>
+        <p className={`${s.prose} mt-2 max-w-2xl`}>
+          What is measured, what is cited from elsewhere, and what we have deliberately not measured
+          all live on one page.
+        </p>
+        <div className="mt-4 flex flex-col gap-3 sm:flex-row">
+          <Link className={s.btnSecondary} to={routes.honesty}>
+            Honesty
+          </Link>
+          <a className={s.btnSecondary} href={REPO_URL} rel="noreferrer noopener" target="_blank">
+            The source on GitHub
+          </a>
+        </div>
+      </div>
+    </main>
+  );
+}