Phase 2: learning engine — history, SRS review, mistakes, stats, exam, reminders

Answer history and schedules
- Every answer is recorded (deck, activity, topic, correct/wrong, time)
  in a versioned IndexedDB log (freezmo-learning v1, stores answers +
  srs), mirrored in memory for synchronous React reads and capped at
  20k answers (oldest pruned). StudyFeed records as it grades.
- Light SM-2 schedule per activity: 1 day, 3 days, then interval x
  ease; wrong answers return in ten minutes with the ease nudged down.

Review, mistakes, stats
- Library 'Smart review' card: due count, mistakes count (latest
  answer wrong — clears itself when answered correctly), today's goal
  progress. Review sessions freeze their item list at start.
- New /review (due across decks, ?mistakes=1 global or ?deck= per
  deck) built on a shared SessionFeed with the study feed's snap/keyboard
  mechanics, wake lock and a results slide.
- New /stats: day streak, five-week calendar, accuracy per subject and
  per deck, weakest topics (>=3 answers), daily-goal progress.
- Daily goal configurable in Settings (10/20/30/50).

Exam mode
- New /exam: pick decks, question count, optional timer; no hints
  (a NoHints context hides hint rows and the self-check escape);
  results with score, per-deck and per-topic breakdown; wrong answers
  land in the mistakes set through the normal history.

Reminders (conditional)
- VAPID-gated: GET/POST/DELETE /api/push and POST /api/push/test with
  the standard route pattern, RATE_LIMIT_PUSH, zod, auth before body.
  Subscriptions stored server-side as endpoint + keys only (PUSH_DIR).
  UI hidden entirely without keys; iOS install note; service worker
  push/notificationclick handlers; scripts/send-reminders.mjs for a
  cron/systemd timer; web-push added as the one server dependency.

Verified: new phase-2 suite 42/42 (history/SRS shapes from a real study
run, mistakes clearing, review session, stats math, exam timer and
breakdowns, VAPID-less hidden state plus the configured
subscribe/validate/test/delete path against a second instance) plus
regression 74/74, mobile 52/52, wizard 80/80, declutter 116/116,
animation 8/8, native 35/35, phase1 38/38, i18n 25/25. Key parity
709/709. Lint + build clean. SW freezmo-v26.

components/activities/shared.tsx

@@ -1,6 +1,7 @@
 "use client";
 
 import { motion, useReducedMotion } from "framer-motion";
+import { createContext, useContext } from "react";
 
 import { useI18n } from "@/lib/i18n";
 import type { Activity } from "@/lib/schemas";
@@ -21,6 +22,8 @@ export type ActivityComponentProps<A extends Activity = Activity> = {
   isLast: boolean;
   /** Overrides the feedback button label (the homework guide uses this). */
   nextLabel?: string;
+  /** Exam mode: hide hint rows and answer-reveal affordances. */
+  noHints?: boolean;
 };
 
 export const TYPE_META: Record<Activity["type"], { labelKey: string; icon: string; tint: string }> = {
@@ -213,5 +216,22 @@ export function FeedbackPanel({
 
 /** Small hint row under a question, e.g. "Tap a term, then its definition". */
 export function Hint({ children }: { children: React.ReactNode }) {
+  const noHints = useNoHints();
+  if (noHints) return null;
   return <p className="text-sm text-frost-600 dark:text-frost-300">{children}</p>;
 }
+
+/**
+ * Exam mode sets this through ActivityRenderer's `noHints` prop so the
+ * affordances that give the answer away disappear without touching every
+ * activity component.
+ */
+const NoHintsContext = createContext(false);
+
+export function NoHintsProvider({ value, children }: { value: boolean; children: React.ReactNode }) {
+  return <NoHintsContext.Provider value={value}>{children}</NoHintsContext.Provider>;
+}
+
+export function useNoHints(): boolean {
+  return useContext(NoHintsContext);
+}