perf: replace N+1 dedup queries with batch pre-fetch in convertCandidates

- convertQuizCandidates: batch findMany all stems before loop, dedup in-memory
- convertFlashcardCandidates: batch findMany all fronts before loop, dedup in-memory
- 50 items now = 1 query instead of 50
- Update tests: mock findMany instead of per-item findFirst

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/modules/ai-runtime/internal/runtime-internal.service.spec.ts

@@ -67,8 +67,8 @@ describe('RuntimeInternalService', () => {
     mockQuestionGenerationPlan = { updateMany: jest.fn() };
     mockFlashcardGenerationPlan = { updateMany: jest.fn() };
     mockQuiz = { create: jest.fn(), update: jest.fn() };
-    mockQuizQuestion = { findFirst: jest.fn(), create: jest.fn() };
-    mockFlashcard = { findFirst: jest.fn(), create: jest.fn() };
+    mockQuizQuestion = { findMany: jest.fn(), create: jest.fn() };
+    mockFlashcard = { findMany: jest.fn(), create: jest.fn() };
     mockKnowledgeItem = { findMany: jest.fn().mockResolvedValue([]) };
     mockNotification = { create: jest.fn() };
 
@@ -558,7 +558,7 @@ describe('RuntimeInternalService', () => {
       mockAiRuntimeJob.update.mockResolvedValue({});
       mockQuestionGenerationPlan.updateMany.mockResolvedValue({ count: 1 });
       mockQuiz.create.mockResolvedValue({ id: 'quiz-1' });
-      mockQuizQuestion.findFirst.mockResolvedValue(null);
+      mockQuizQuestion.findMany.mockResolvedValue([]);
       mockQuizQuestion.create.mockResolvedValue({});
 
       await service.submitResult('j1', qDto);
@@ -576,7 +576,7 @@ describe('RuntimeInternalService', () => {
       mockAiRuntimeResult.create.mockResolvedValue({});
       mockAiRuntimeJob.update.mockResolvedValue({});
       mockFlashcardGenerationPlan.updateMany.mockResolvedValue({ count: 1 });
-      mockFlashcard.findFirst.mockResolvedValue(null);
+      mockFlashcard.findMany.mockResolvedValue([]);
       mockFlashcard.create.mockResolvedValue({});
 
       await service.submitResult('j1', fcDto);
@@ -860,7 +860,7 @@ describe('RuntimeInternalService', () => {
       mockAiRuntimeJob.update.mockResolvedValue({});
       mockQuestionGenerationPlan.updateMany.mockResolvedValue({ count: 1 });
       mockQuiz.create.mockResolvedValue({ id: 'quiz-1' });
-      mockQuizQuestion.findFirst.mockResolvedValue(null);
+      mockQuizQuestion.findMany.mockResolvedValue([]);
       mockQuizQuestion.create.mockResolvedValue({});
     });
 
@@ -892,8 +892,8 @@ describe('RuntimeInternalService', () => {
     it('skips duplicate questions (same stem for user)', async () => {
       const loggerSpy = jest.spyOn((service as any).logger, 'warn');
       mockAiRuntimeJob.findUnique.mockResolvedValue(qJob);
-      mockQuizQuestion.findFirst.mockResolvedValueOnce({ id: 'existing-q' }); // duplicate
-      mockQuizQuestion.findFirst.mockResolvedValueOnce(null); // unique
+      // Batch dedup: findMany returns existing stems; 'Duplicate?' is duplicate, 'Unique?' is new
+      mockQuizQuestion.findMany.mockResolvedValue([{ stem: 'Duplicate?' }]);
       mockQuiz.update.mockResolvedValue({});
 
       await service.submitResult('j1', {
@@ -946,7 +946,7 @@ describe('RuntimeInternalService', () => {
       mockAiRuntimeResult.create.mockResolvedValue({});
       mockAiRuntimeJob.update.mockResolvedValue({});
       mockFlashcardGenerationPlan.updateMany.mockResolvedValue({ count: 1 });
-      mockFlashcard.findFirst.mockResolvedValue(null);
+      mockFlashcard.findMany.mockResolvedValue([]);
       mockFlashcard.create.mockResolvedValue({});
     });
 
@@ -966,8 +966,8 @@ describe('RuntimeInternalService', () => {
     it('skips duplicate cards (same front for user)', async () => {
       const loggerSpy = jest.spyOn((service as any).logger, 'warn');
       mockAiRuntimeJob.findUnique.mockResolvedValue(fcJob);
-      mockFlashcard.findFirst.mockResolvedValueOnce({ id: 'dup-1' });
-      mockFlashcard.findFirst.mockResolvedValueOnce(null);
+      // Batch dedup: findMany returns existing fronts; 'Dup' is duplicate, 'Unique' is new
+      mockFlashcard.findMany.mockResolvedValue([{ front: 'Dup' }]);
 
       await service.submitResult('j1', {
         runtimeInstanceId: 'rt-1', schemaVersion: 'ov1', status: 'succeeded',

src/modules/ai-runtime/internal/runtime-internal.service.ts

@@ -458,19 +458,24 @@ export class RuntimeInternalService {
     });
 
     let created = 0;
-    for (let i = 0; i < valid.length; i++) {
-      const q = valid[i];
-      const stem = q.stem ?? q.question;
 
-      // Dedup: skip if same stem already exists for this user in any quiz
-      const existing = await this.prisma.quizQuestion.findFirst({
+    // Batch pre-fetch existing stems for dedup (avoids N+1 per-item queries)
+    const stems = valid.map(q => q.stem ?? q.question);
+    const existingStems = new Set(
+      (await this.prisma.quizQuestion.findMany({
         where: {
-          stem,
+          stem: { in: stems },
           quiz: { userId: job.userId },
         },
-        select: { id: true },
-      });
-      if (existing) {
+        select: { stem: true },
+      })).map(r => r.stem),
+    );
+
+    for (let i = 0; i < valid.length; i++) {
+      const q = valid[i];
+      const stem = stems[i];
+
+      if (existingStems.has(stem)) {
         this.logger.warn(`convertQuizCandidates: skipping duplicate question stem="${stem.substring(0, 50)}"`);
         continue;
       }
@@ -521,6 +526,15 @@ export class RuntimeInternalService {
         )
       : new Set<string>();
 
+    // Batch pre-fetch existing fronts for dedup (avoids N+1 per-item queries)
+    const fronts = valid.map(c => c.front ?? c.question);
+    const existingFronts = new Set(
+      (await this.prisma.flashcard.findMany({
+        where: { userId: job.userId, front: { in: fronts }, deletedAt: null },
+        select: { front: true },
+      })).map(r => r.front),
+    );
+
     for (const card of valid) {
       const rawIds: string[] = Array.isArray(card.sourceBlockIds) ? card.sourceBlockIds : [];
       const validIds = rawIds.filter(id => existingBlockIds.has(id));
@@ -528,14 +542,8 @@ export class RuntimeInternalService {
         this.logger.warn(`convertFlashcardCandidates: filtered ${rawIds.length - validIds.length} invalid sourceBlockIds`);
       }
 
-
-      // Dedup: skip if same front already exists for this user
       const front = card.front ?? card.question;
-      const dupCheck = await this.prisma.flashcard.findFirst({
-        where: { userId: job.userId, front, deletedAt: null },
-        select: { id: true },
-      });
-      if (dupCheck) {
+      if (existingFronts.has(front)) {
         this.logger.warn(`convertFlashcardCandidates: skipping duplicate front="${front.substring(0, 50)}"`);
         continue;
       }