feat(quiz): variety in quiz question selection

Expand the seeded pool from 12 to 36 questions (migration 0020) and
select 10 per session preferring questions the couple has never seen,
then least recently used, with random tiebreaks, so repeat quizzes stop
serving the same set.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

apps/api/test/quiz.integration.test.ts

@@ -21,6 +21,7 @@ describe.skipIf(!url || !local)('quiz + PostgreSQL', () => {
   const couple = '55555555-5555-4555-8555-555555555555';
   const soloCouple = '66666666-6666-4666-8666-666666666666';
   const otherCouple = '77777777-7777-4777-8777-777777777777';
+  const userC = '88888888-8888-4888-8888-888888888888';
 
   beforeAll(async () => {
     await admin.query(`create schema "${schema}"`);
@@ -44,8 +45,8 @@ describe.skipIf(!url || !local)('quiz + PostgreSQL', () => {
     );
     await pool.query(
       `insert into profiles(id,couple_id) values
-        ($1,$5),($2,$5),($3,$6),($4,$7)`,
-      [userA, userB, soloUser, outsider, couple, soloCouple, otherCouple],
+        ($1,$5),($2,$5),($3,$6),($4,$7),($8,$7)`,
+      [userA, userB, soloUser, outsider, couple, soloCouple, otherCouple, userC],
     );
   });
 
@@ -206,4 +207,44 @@ describe.skipIf(!url || !local)('quiz + PostgreSQL', () => {
     const current = await repo.currentSession(userB);
     expect(current?.id).toBe(session.id);
   });
+
+  it('draws the next session from never-used questions once a session completes', async () => {
+    const { session: first } = await repo.startSession(userA);
+    const firstQuestionIds = first.questions.map((question) => question.id);
+    expect(firstQuestionIds).toHaveLength(10);
+
+    const answers = firstQuestionIds.map((id) => ({ question_id: id, self_index: 0, guess_index: 0 }));
+    await repo.submitAnswers(userA, first.id, answers);
+    const completed = await repo.submitAnswers(userB, first.id, answers);
+    expect(completed.status).toBe('completed');
+
+    const { session: second, created } = await repo.startSession(userA);
+    expect(created).toBe(true);
+    const secondQuestionIds = second.questions.map((question) => question.id);
+    expect(secondQuestionIds).toHaveLength(10);
+
+    // The seeded pool has 36 active questions, so the never-used-first preference
+    // guarantees the second session's questions are wholly disjoint from the first.
+    const overlap = secondQuestionIds.filter((id) => firstQuestionIds.includes(id));
+    expect(overlap).toEqual([]);
+  });
+
+  it('scopes selection to each couple independently', async () => {
+    const { session: coupleOneFirst } = await repo.startSession(userA);
+    const coupleOneFirstIds = coupleOneFirst.questions.map((question) => question.id);
+    const answers = coupleOneFirstIds.map((id) => ({ question_id: id, self_index: 0, guess_index: 0 }));
+    await repo.submitAnswers(userA, coupleOneFirst.id, answers);
+    await repo.submitAnswers(userB, coupleOneFirst.id, answers);
+
+    // A different couple with no prior sessions should still be able to draw a
+    // fresh set of 10 questions regardless of what the first couple has used,
+    // since the never-used-for-them preference is scoped per couple.
+    const { session: otherSession, created } = await repo.startSession(outsider);
+    expect(created).toBe(true);
+    expect(otherSession.questions).toHaveLength(10);
+
+    const partnerView = await repo.startSession(userC);
+    expect(partnerView.created).toBe(false);
+    expect(partnerView.session.id).toBe(otherSession.id);
+  });
 });