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.

lib/schemas.ts

@@ -280,3 +280,33 @@ export const deckSchema: z.ZodType<Deck> = z.object({
   attempts: z.number(),
   bestScore: z.number().optional(),
 });
+
+/* ------------------------------------------------------------------ */
+/* Learning history (IndexedDB, included in backups and sync)          */
+/* ------------------------------------------------------------------ */
+
+export const answerRecordSchema = z.object({
+  id: z.string().min(1).max(80),
+  deckId: z.string().min(1).max(80),
+  deckTitle: z.string().max(200),
+  activityId: z.string().min(1).max(80),
+  type: z.string().max(40),
+  topic: z.string().max(120).optional(),
+  correct: z.boolean(),
+  at: z.number(),
+});
+export type AnswerRecord = z.infer<typeof answerRecordSchema>;
+
+export const srsRecordSchema = z.object({
+  key: z.string().min(1).max(200),
+  deckId: z.string().min(1).max(80),
+  activityId: z.string().min(1).max(80),
+  ease: z.number().min(1).max(4),
+  reps: z.number().int().min(0).max(1000),
+  intervalDays: z.number().int().min(0).max(3650),
+  lapses: z.number().int().min(0).max(10000),
+  dueAt: z.number(),
+  lastAt: z.number(),
+  lastCorrect: z.boolean(),
+});
+export type SrsRecord = z.infer<typeof srsRecordSchema>;