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/config.ts

@@ -31,6 +31,7 @@ export type ServerConfig = {
     homework: number;
     health: number;
     sync: number;
+    push: number;
   };
   sync: {
     /** Where opaque encrypted sync blobs live (SYNC_DIR). */
@@ -40,6 +41,14 @@ export type ServerConfig = {
     /** Total cap for the whole directory in bytes (SYNC_TOTAL_BYTES). */
     totalBytes: number;
   };
+  push: {
+    /** VAPID keys — reminders are hidden entirely when either is empty. */
+    publicKey: string;
+    privateKey: string;
+    subject: string;
+    /** Where push subscriptions live (PUSH_DIR). */
+    dir: string;
+  };
 };
 
 /** What a single request should use to talk to Ollama. */
@@ -111,12 +120,20 @@ export function getServerConfig(): ServerConfig {
       health: positiveInt(process.env.RATE_LIMIT_HEALTH, 90),
       // Sync is cheap (no model calls) but shouldn't be hammered.
       sync: positiveInt(process.env.RATE_LIMIT_SYNC, 60),
+      // Push subscription changes and test sends.
+      push: positiveInt(process.env.RATE_LIMIT_PUSH, 30),
     },
     sync: {
       dir: process.env.SYNC_DIR?.trim() || path.join(process.cwd(), ".freezmo", "sync"),
       maxBytes: positiveInt(process.env.SYNC_MAX_BYTES, 12 * 1024 * 1024),
       totalBytes: positiveInt(process.env.SYNC_TOTAL_BYTES, 1024 * 1024 * 1024),
     },
+    push: {
+      publicKey: process.env.VAPID_PUBLIC_KEY?.trim() || "",
+      privateKey: process.env.VAPID_PRIVATE_KEY?.trim() || "",
+      subject: process.env.VAPID_SUBJECT?.trim() || "mailto:freezmo@localhost",
+      dir: process.env.PUSH_DIR?.trim() || path.join(process.cwd(), ".freezmo", "push"),
+    },
   };
 }