diff --git a/backend/src/migration/interfaces/puzzle.interface.ts b/backend/src/migration/interfaces/puzzle.interface.ts
index 7515e45f..413126b4 100644
--- a/backend/src/migration/interfaces/puzzle.interface.ts
+++ b/backend/src/migration/interfaces/puzzle.interface.ts
@@ -52,6 +52,11 @@ export interface MigrationResult {
     failedInserts: number;
     duplicatesSkipped: number;
   };
+  /**
+   * True when the import was aborted mid-way and the whole batch was
+   * rolled back, so no partial data was persisted.
+   */
+  rolledBack: boolean;
   errors: MigrationError[];
   uploadInfo: {
     filename: string;
diff --git a/backend/src/migration/services/migration.service.spec.ts b/backend/src/migration/services/migration.service.spec.ts
new file mode 100644
index 00000000..6952d712
--- /dev/null
+++ b/backend/src/migration/services/migration.service.spec.ts
@@ -0,0 +1,142 @@
+import { Test, TestingModule } from '@nestjs/testing';
+import { DataSource } from 'typeorm';
+import { getRepositoryToken } from '@nestjs/typeorm';
+import { MigrationService } from './migration.service';
+import { Puzzle } from '../entities/puzzle.entity';
+import { PuzzleData } from '../interfaces/puzzle.interface';
+
+function makePuzzle(title: string, category = 'math'): PuzzleData {
+  return {
+    title,
+    category,
+    difficulty: 'easy',
+    content: {
+      question: 'Question for ' + title,
+      answer: '42',
+      type: 'text',
+    },
+  };
+}
+
+describe('MigrationService (atomic / resumable import)', () => {
+  let service: MigrationService;
+  let dataSource: {
+    transaction: jest.Mock;
+  };
+  let puzzleRepository: {
+    findOne: jest.Mock;
+    create: jest.Mock;
+    save: jest.Mock;
+  };
+
+  // Shared manager object handed to the transaction callback. It returns
+  // the same fake puzzle repository regardless of which repository is
+  // requested, so state can be inspected after a run.
+  const buildManager = () => ({
+    getRepository: jest.fn(() => puzzleRepository),
+  });
+
+  beforeEach(async () => {
+    dataSource = {
+      transaction: jest.fn(),
+    };
+    puzzleRepository = {
+      findOne: jest.fn(),
+      create: jest.fn((data) => ({ id: 'new-id', ...data })),
+      save: jest.fn(async (data) => data),
+    };
+
+    const module: TestingModule = await Test.createTestingModule({
+      providers: [
+        MigrationService,
+        {
+          provide: DataSource,
+          useValue: dataSource,
+        },
+        {
+          provide: getRepositoryToken(Puzzle),
+          useValue: puzzleRepository,
+        },
+      ],
+    }).compile();
+
+    service = module.get<MigrationService>(MigrationService);
+  });
+
+  const uploadInfo = { filename: 'f.json', fileSize: 10, uploadedBy: 'admin' };
+
+  it('imports every row on a clean batch', async () => {
+    puzzleRepository.findOne.mockResolvedValue(undefined);
+
+    // Run the provided transaction callback against the fake manager.
+    dataSource.transaction.mockImplementation(async (cb) => cb(buildManager()));
+
+    const result = await service.migratePuzzles(
+      [makePuzzle('A'), makePuzzle('B')],
+      uploadInfo,
+    );
+
+    expect(result.success).toBe(true);
+    expect(result.rolledBack).toBe(false);
+    expect(result.summary.successfulInserts).toBe(2);
+    expect(result.summary.failedInserts).toBe(0);
+    expect(result.summary.duplicatesSkipped).toBe(0);
+    expect(puzzleRepository.save).toHaveBeenCalledTimes(2);
+  });
+
+  it('aborts and rolls back the whole batch when a row fails mid-import', async () => {
+    puzzleRepository.findOne.mockResolvedValue(undefined);
+
+    // Simulate the transaction throwing when the callback is run.
+    let manager: ReturnType<typeof buildManager>;
+    dataSource.transaction.mockImplementation(async (cb) => {
+      manager = buildManager();
+      puzzleRepository.save.mockReset();
+      puzzleRepository.save
+        .mockResolvedValueOnce({ id: 'a' })
+        .mockImplementationOnce(async () => {
+          throw new Error('unique constraint violated on in-batch duplicate');
+        });
+      try {
+        return await cb(manager);
+      } catch (err) {
+        // The real DataSource rolls back and rethrows here.
+        throw err;
+      }
+    });
+
+    const result = await service.migratePuzzles(
+      [makePuzzle('A'), makePuzzle('A')], // in-batch duplicate -> unique index error
+      uploadInfo,
+    );
+
+    expect(result.success).toBe(false);
+    expect(result.rolledBack).toBe(true);
+    // Because the transaction rolled back, nothing counted as persisted.
+    expect(result.summary.successfulInserts).toBe(0);
+    expect(result.summary.failedInserts).toBe(1);
+    expect(result.errors[0].error).toContain('rolled back');
+    expect(result.errors[0].index).toBe(1);
+  });
+
+  it('skips pre-existing rows so re-running the import is resumable', async () => {
+    // Row 'A' already exists in the DB; 'B' does not.
+    puzzleRepository.findOne.mockImplementation(async ({ where }) => {
+      return where.title === 'A' ? { id: 'existing' } : undefined;
+    });
+
+    dataSource.transaction.mockImplementation(async (cb) => cb(buildManager()));
+
+    const result = await service.migratePuzzles(
+      [makePuzzle('A'), makePuzzle('B')],
+      uploadInfo,
+    );
+
+    expect(result.success).toBe(true);
+    expect(result.rolledBack).toBe(false);
+    expect(result.summary.duplicatesSkipped).toBe(1);
+    expect(result.summary.successfulInserts).toBe(1);
+    // Only the non-duplicate row is saved.
+    expect(puzzleRepository.save).toHaveBeenCalledTimes(1);
+  });
+});
diff --git a/backend/src/migration/services/migration.service.ts b/backend/src/migration/services/migration.service.ts
index b451c3a9..07f3401c 100644
--- a/backend/src/migration/services/migration.service.ts
+++ b/backend/src/migration/services/migration.service.ts
@@ -1,20 +1,50 @@
 import { Injectable, Logger } from '@nestjs/common';
-import type { Repository } from 'typeorm';
-import type { Puzzle } from '../entities/puzzle.entity';
+import { InjectRepository } from '@nestjs/typeorm';
+import { DataSource, EntityManager, Repository } from 'typeorm';
+import { Puzzle } from '../entities/puzzle.entity';
 import type {
   PuzzleData,
   MigrationResult,
   MigrationError,
 } from '../interfaces/puzzle.interface';
 
+/**
+ * Thrown inside the migration transaction to abort the whole batch. Any
+ * error that escapes the transaction callback rolls back every row so a
+ * partial import can never leave categories/puzzles/dependencies/rewards
+ * in an inconsistent state.
+ */
+export class MigrationAbortError extends Error {
+  constructor(
+    readonly index: number,
+    readonly puzzle: Partial<PuzzleData>,
+    message: string,
+  ) {
+    super(message);
+    this.name = 'MigrationAbortError';
+  }
+}
+
 @Injectable()
 export class MigrationService {
   private readonly logger = new Logger(MigrationService.name);
 
-  constructor(private readonly puzzleRepository: Repository<Puzzle>) {}
+  constructor(
+    private readonly dataSource: DataSource,
+    @InjectRepository(Puzzle)
+    private readonly puzzleRepository: Repository<Puzzle>,
+  ) {}
 
   /**
-   * Migrate puzzle data to database
+   * Migrate puzzle data to database.
+   *
+   * The whole batch runs inside a single DB transaction (atomic import):
+   * if any row fails to persist, the transaction rolls back and nothing is
+   * written. Rows whose `(title, category)` pair already exists in the DB
+   * are skipped so re-running the same upload is safe and resumable, but a
+   * genuine failure (e.g. a duplicate pair within the same incoming batch,
+   * which violates the unique index) aborts the entire import rather than
+   * leaving a partial write behind.
    */
   async migratePuzzles(
     puzzleData: PuzzleData[],
@@ -25,57 +55,90 @@ export class MigrationService {
     const errors: MigrationError[] = [];
     let successfulInserts = 0;
     let duplicatesSkipped = 0;
-
-    for (let i = 0; i < puzzleData.length; i++) {
-      const puzzle = puzzleData[i];
-
-      try {
-        // Check for duplicates
-        const existingPuzzle = await this.puzzleRepository.findOne({
-          where: {
-            title: puzzle.title,
-            category: puzzle.category,
-          },
-        });
-
-        if (existingPuzzle) {
-          this.logger.warn(
-            `Duplicate puzzle found: ${puzzle.title} in category ${puzzle.category}`,
-          );
-          duplicatesSkipped++;
-          continue;
+    let rolledBack = false;
+
+    try {
+      await this.dataSource.transaction(async (manager: EntityManager) => {
+        const puzzleRepo = manager.getRepository(Puzzle);
+
+        for (let i = 0; i < puzzleData.length; i++) {
+          const puzzle = puzzleData[i];
+
+          try {
+            // Check for duplicates against rows already in the DB. Pre-existing
+            // duplicates are skipped (idempotent/resumable), not failures.
+            const existingPuzzle = await puzzleRepo.findOne({
+              where: {
+                title: puzzle.title,
+                category: puzzle.category,
+              },
+            });
+
+            if (existingPuzzle) {
+              this.logger.warn(
+                `Duplicate puzzle found: ${puzzle.title} in category ${puzzle.category}`,
+              );
+              duplicatesSkipped++;
+              continue;
+            }
+
+            // Create new puzzle entity
+            const newPuzzle = puzzleRepo.create({
+              title: puzzle.title,
+              description: puzzle.description,
+              difficulty: puzzle.difficulty,
+              category: puzzle.category,
+              content: puzzle.content,
+              metadata: puzzle.metadata,
+              tags: puzzle.tags,
+              isActive: puzzle.isActive,
+            });
+
+            await puzzleRepo.save(newPuzzle);
+            successfulInserts++;
+
+            this.logger.debug(`Successfully inserted puzzle: ${puzzle.title}`);
+          } catch (error) {
+            // Wrap with row context, then rethrow so the surrounding
+            // transaction rolls back every already-inserted row.
+            throw new MigrationAbortError(
+              i,
+              puzzle,
+              error instanceof Error ? error.message : String(error),
+            );
+          }
         }
-
-        // Create new puzzle entity
-        const newPuzzle = this.puzzleRepository.create({
-          title: puzzle.title,
-          description: puzzle.description,
-          difficulty: puzzle.difficulty,
-          category: puzzle.category,
-          content: puzzle.content,
-          metadata: puzzle.metadata,
-          tags: puzzle.tags,
-          isActive: puzzle.isActive,
-        });
-
-        await this.puzzleRepository.save(newPuzzle);
-        successfulInserts++;
-
-        this.logger.debug(`Successfully inserted puzzle: ${puzzle.title}`);
-      } catch (error) {
-        this.logger.error(
-          `Failed to insert puzzle at index ${i}: ${error.message}`,
-        );
-        errors.push({
-          index: i,
-          puzzle,
-          error: error.message,
-        });
-      }
+      });
+    } catch (error) {
+      // Any error here aborts the transaction, rolling back every row that
+      // the batch may have inserted before failing. Record the abort so the
+      // caller can see the import did not partially apply.
+      const abortError =
+        error instanceof MigrationAbortError
+          ? error
+          : new MigrationAbortError(
+              -1,
+              {},
+              error instanceof Error ? error.message : String(error),
+            );
+
+      rolledBack = true;
+      // The transaction rolled back, so nothing was actually persisted:
+      // report zero successful inserts and every row as not applied.
+      successfulInserts = 0;
+      errors.push({
+        index: abortError.index,
+        puzzle: abortError.puzzle,
+        error: `Import aborted and rolled back: ${abortError.message}`,
+      });
+
+      this.logger.error(
+        `Migration aborted and rolled back (row ${abortError.index}): ${abortError.message}`,
+      );
     }
 
     const result: MigrationResult = {
-      success: errors.length === 0,
+      success: !rolledBack && errors.length === 0,
       summary: {
         totalProcessed: puzzleData.length,
         successfulInserts,
@@ -83,6 +146,7 @@ export class MigrationService {
         duplicatesSkipped,
       },
       errors,
+      rolledBack,
       uploadInfo: {
         ...uploadInfo,
         uploadedAt: new Date(),
@@ -90,7 +154,7 @@ export class MigrationService {
     };
 
     this.logger.log(
-      `Migration completed: ${successfulInserts} inserted, ${duplicatesSkipped} duplicates skipped, ${errors.length} failed`,
+      `Migration completed: ${successfulInserts} inserted, ${duplicatesSkipped} duplicates skipped, ${errors.length} failed${rolledBack ? ' (rolled back)' : ''}`,
     );
 
     return result;