feat: optimize state updates using flushSync for smoother exam transitions

frontend/src/App.tsx

@@ -1,4 +1,5 @@
 import { useState, useEffect, useCallback } from "react";
+import { flushSync } from "react-dom";
 import {
   useNavigate,
   useLocation,
@@ -136,15 +137,17 @@ function AppInner() {
       tweaks.feedbackMode === "auto"
         ? (data.feedbackMode ?? "end")
         : tweaks.feedbackMode;
-    setExam(data);
-    setExamState({
-      currentIdx: 0,
-      answers: {},
-      flags: {},
-      notes: "",
-      revealed: {},
-      startedAt: Date.now(),
-      feedbackMode: fm,
+    flushSync(() => {
+      setExam(data);
+      setExamState({
+        currentIdx: 0,
+        answers: {},
+        flags: {},
+        notes: "",
+        revealed: {},
+        startedAt: Date.now(),
+        feedbackMode: fm,
+      });
     });
     navigate(`/exam/${slugify(data.title)}/q1`);
   };
@@ -152,8 +155,10 @@ function AppInner() {
   const resume = () => {
     const saved = loadState();
     if (saved?.exam && saved?.state) {
-      setExam(saved.exam);
-      setExamState(withNotes(saved.state));
+      flushSync(() => {
+        setExam(saved.exam);
+        setExamState(withNotes(saved.state));
+      });
       navigate(
         `/exam/${slugify(saved.exam.title)}/q${saved.state.currentIdx + 1}`,
       );
@@ -235,18 +240,24 @@ function AppInner() {
         completedAt: number;
       }>(`/api/results/${remoteId}`)
         .then((data) => {
-          setExam(data.exam);
-          setExamState(withNotes(data.state));
+          flushSync(() => {
+            setExam(data.exam);
+            setExamState(withNotes(data.state));
+          });
           navigate(`/review/${slugify(entry.title)}`);
         })
         .catch(() => {
-          setExam(entry.exam);
-          setExamState(withNotes(entry.state));
+          flushSync(() => {
+            setExam(entry.exam);
+            setExamState(withNotes(entry.state));
+          });
           navigate(`/review/${slugify(entry.title)}`);
         });
     } else {
-      setExam(entry.exam);
-      setExamState(withNotes(entry.state));
+      flushSync(() => {
+        setExam(entry.exam);
+        setExamState(withNotes(entry.state));
+      });
       navigate(`/review/${slugify(entry.title)}`);
     }
   };