fix(auth): stop Turnstile SSR/client hydration mismatch on /login

components/security/Turnstile.tsx

@@ -63,16 +63,27 @@ export function Turnstile({
   // Cloudflare throws error 110200 and retries forever. Skip the real challenge
   // there — hand the form a sentinel, and the server bypasses Turnstile for
   // localhost too (lib/turnstile/verify.ts). Production is unaffected.
-  const isLocalhost = typeof window !== 'undefined'
-    && /^(localhost|127\.0\.0\.1|0\.0\.0\.0|\[::1\])$|\.local$/i.test(window.location.hostname);
+  //
+  // MUST default false and only flip after mount: the server can't read
+  // window.location, so deriving this synchronously from `window` made the SSR
+  // HTML (widget div) diverge from the client's first paint (null) on localhost
+  // — a hydration mismatch. Starting false keeps SSR and first client paint
+  // identical; the effect flips it (and fires the bypass token) post-hydration.
+  const isLocal = () => /^(localhost|127\.0\.0\.1|0\.0\.0\.0|\[::1\])$|\.local$/i.test(window.location.hostname);
+  const [isLocalhost, setIsLocalhost] = useState(false);
 
   useEffect(() => {
-    if (isLocalhost) onTokenRef.current('localhost-dev-bypass');
-  }, [isLocalhost]);
+    if (isLocal()) {
+      setIsLocalhost(true);
+      onTokenRef.current('localhost-dev-bypass');
+    }
+  }, []);
 
-  // Mount: render exactly one widget; clean it up on unmount.
+  // Mount: render exactly one widget; clean it up on unmount. Read localhost
+  // straight from window here (not the state, which lands a tick later) so the
+  // doomed real challenge is never kicked off on a dev host.
   useEffect(() => {
-    if (!SITE_KEY || isLocalhost) return;
+    if (!SITE_KEY || isLocal()) return;
     let cancelled = false;
     let poll: ReturnType<typeof setInterval> | undefined;
     let giveUp: ReturnType<typeof setTimeout> | undefined;

package.json

@@ -27,7 +27,7 @@
     "test:pill-tap": "node scripts/eval-pill-tap.mjs",
     "test:stale-state": "node scripts/eval-stale-state.mjs",
     "test:intent-live": "node scripts/eval-intent-matrix.mjs",
-    "clean": "next clean"
+    "clean": "rm -rf .next"
   },
   "dependencies": {
     "@google-analytics/data": "^5.2.1",