diff --git a/changelog.md b/changelog.md
index 69be86f..5f3ec36 100644
--- a/changelog.md
+++ b/changelog.md
@@ -1,5 +1,16 @@
 # Changelog
 
+## 2026-02-01 - 4.1.1 - fix(tsmdb)
+add comprehensive unit tests for tsmdb components: checksum, query planner, index engine, session, and WAL
+
+- Add new tests: test.tsmdb.checksum.ts — CRC32 and document checksum utilities (add/verify/remove)
+- Add new tests: test.tsmdb.queryplanner.ts — QueryPlanner plans, index usage, selectivity, explain output, and edge cases
+- Add new tests: test.tsmdb.indexengine.ts — Index creation, unique/sparse options, candidate selection, and constraints
+- Add new tests: test.tsmdb.session.ts — Session lifecycle, touch/refresh/close, extractSessionId handling
+- Add new tests: test.tsmdb.wal.ts — WAL initialization, LSN increments, logging/recovery for inserts/updates/deletes, binary and nested data handling
+- Tests only — no production API changes; increases test coverage
+- Recommend patch bump from 4.1.0 to 4.1.1
+
 ## 2026-02-01 - 4.1.0 - feat(readme)
 expand README with storage integrity, WAL, query planner, session & transaction docs; update test script to enable verbose logging and increase timeout
 
diff --git a/test/test.tsmdb.checksum.ts b/test/test.tsmdb.checksum.ts
new file mode 100644
index 0000000..909ec1e
--- /dev/null
+++ b/test/test.tsmdb.checksum.ts
@@ -0,0 +1,232 @@
+import { expect, tap } from '@git.zone/tstest/tapbundle';
+import * as smartmongo from '../ts/index.js';
+
+const {
+  calculateCRC32,
+  calculateCRC32Buffer,
+  calculateDocumentChecksum,
+  addChecksum,
+  verifyChecksum,
+  removeChecksum,
+} = smartmongo.tsmdb;
+
+// ============================================================================
+// CRC32 String Tests
+// ============================================================================
+
+tap.test('checksum: calculateCRC32 should return consistent value for same input', async () => {
+  const result1 = calculateCRC32('hello world');
+  const result2 = calculateCRC32('hello world');
+  expect(result1).toEqual(result2);
+});
+
+tap.test('checksum: calculateCRC32 should return different values for different inputs', async () => {
+  const result1 = calculateCRC32('hello');
+  const result2 = calculateCRC32('world');
+  expect(result1).not.toEqual(result2);
+});
+
+tap.test('checksum: calculateCRC32 should return a 32-bit unsigned integer', async () => {
+  const result = calculateCRC32('test string');
+  expect(result).toBeGreaterThanOrEqual(0);
+  expect(result).toBeLessThanOrEqual(0xFFFFFFFF);
+});
+
+tap.test('checksum: calculateCRC32 should handle empty string', async () => {
+  const result = calculateCRC32('');
+  expect(typeof result).toEqual('number');
+  expect(result).toBeGreaterThanOrEqual(0);
+});
+
+tap.test('checksum: calculateCRC32 should handle special characters', async () => {
+  const result = calculateCRC32('hello\nworld\t!"#$%&\'()');
+  expect(typeof result).toEqual('number');
+  expect(result).toBeGreaterThanOrEqual(0);
+});
+
+tap.test('checksum: calculateCRC32 should handle unicode characters', async () => {
+  const result = calculateCRC32('hello 世界 🌍');
+  expect(typeof result).toEqual('number');
+  expect(result).toBeGreaterThanOrEqual(0);
+});
+
+// ============================================================================
+// CRC32 Buffer Tests
+// ============================================================================
+
+tap.test('checksum: calculateCRC32Buffer should return consistent value for same input', async () => {
+  const buffer = Buffer.from('hello world');
+  const result1 = calculateCRC32Buffer(buffer);
+  const result2 = calculateCRC32Buffer(buffer);
+  expect(result1).toEqual(result2);
+});
+
+tap.test('checksum: calculateCRC32Buffer should return different values for different inputs', async () => {
+  const buffer1 = Buffer.from('hello');
+  const buffer2 = Buffer.from('world');
+  const result1 = calculateCRC32Buffer(buffer1);
+  const result2 = calculateCRC32Buffer(buffer2);
+  expect(result1).not.toEqual(result2);
+});
+
+tap.test('checksum: calculateCRC32Buffer should handle empty buffer', async () => {
+  const result = calculateCRC32Buffer(Buffer.from(''));
+  expect(typeof result).toEqual('number');
+  expect(result).toBeGreaterThanOrEqual(0);
+});
+
+tap.test('checksum: calculateCRC32Buffer should handle binary data', async () => {
+  const buffer = Buffer.from([0x00, 0xFF, 0x7F, 0x80, 0x01]);
+  const result = calculateCRC32Buffer(buffer);
+  expect(typeof result).toEqual('number');
+  expect(result).toBeGreaterThanOrEqual(0);
+});
+
+// ============================================================================
+// Document Checksum Tests
+// ============================================================================
+
+tap.test('checksum: calculateDocumentChecksum should return consistent value', async () => {
+  const doc = { name: 'John', age: 30 };
+  const result1 = calculateDocumentChecksum(doc);
+  const result2 = calculateDocumentChecksum(doc);
+  expect(result1).toEqual(result2);
+});
+
+tap.test('checksum: calculateDocumentChecksum should exclude _checksum field', async () => {
+  const doc1 = { name: 'John', age: 30 };
+  const doc2 = { name: 'John', age: 30, _checksum: 12345 };
+  const result1 = calculateDocumentChecksum(doc1);
+  const result2 = calculateDocumentChecksum(doc2);
+  expect(result1).toEqual(result2);
+});
+
+tap.test('checksum: calculateDocumentChecksum should handle empty document', async () => {
+  const result = calculateDocumentChecksum({});
+  expect(typeof result).toEqual('number');
+  expect(result).toBeGreaterThanOrEqual(0);
+});
+
+tap.test('checksum: calculateDocumentChecksum should handle nested objects', async () => {
+  const doc = {
+    name: 'John',
+    address: {
+      street: '123 Main St',
+      city: 'Springfield',
+      zip: {
+        code: '12345',
+        plus4: '6789',
+      },
+    },
+  };
+  const result = calculateDocumentChecksum(doc);
+  expect(typeof result).toEqual('number');
+  expect(result).toBeGreaterThanOrEqual(0);
+});
+
+tap.test('checksum: calculateDocumentChecksum should handle arrays', async () => {
+  const doc = {
+    name: 'John',
+    tags: ['developer', 'tester', 'admin'],
+    scores: [95, 87, 92],
+  };
+  const result = calculateDocumentChecksum(doc);
+  expect(typeof result).toEqual('number');
+  expect(result).toBeGreaterThanOrEqual(0);
+});
+
+// ============================================================================
+// Add/Verify/Remove Checksum Tests
+// ============================================================================
+
+tap.test('checksum: addChecksum should add _checksum field to document', async () => {
+  const doc = { name: 'John', age: 30 };
+  const docWithChecksum = addChecksum(doc);
+
+  expect('_checksum' in docWithChecksum).toBeTrue();
+  expect(typeof docWithChecksum._checksum).toEqual('number');
+  expect(docWithChecksum.name).toEqual('John');
+  expect(docWithChecksum.age).toEqual(30);
+});
+
+tap.test('checksum: addChecksum should not modify the original document', async () => {
+  const doc = { name: 'John', age: 30 };
+  addChecksum(doc);
+  expect('_checksum' in doc).toBeFalse();
+});
+
+tap.test('checksum: verifyChecksum should return true for valid checksum', async () => {
+  const doc = { name: 'John', age: 30 };
+  const docWithChecksum = addChecksum(doc);
+  const isValid = verifyChecksum(docWithChecksum);
+  expect(isValid).toBeTrue();
+});
+
+tap.test('checksum: verifyChecksum should return false for tampered document', async () => {
+  const doc = { name: 'John', age: 30 };
+  const docWithChecksum = addChecksum(doc);
+
+  // Tamper with the document
+  docWithChecksum.age = 31;
+
+  const isValid = verifyChecksum(docWithChecksum);
+  expect(isValid).toBeFalse();
+});
+
+tap.test('checksum: verifyChecksum should return false for wrong checksum', async () => {
+  const doc = { name: 'John', age: 30, _checksum: 12345 };
+  const isValid = verifyChecksum(doc);
+  expect(isValid).toBeFalse();
+});
+
+tap.test('checksum: verifyChecksum should return true for document without checksum', async () => {
+  const doc = { name: 'John', age: 30 };
+  const isValid = verifyChecksum(doc);
+  expect(isValid).toBeTrue();
+});
+
+tap.test('checksum: removeChecksum should remove _checksum field', async () => {
+  const doc = { name: 'John', age: 30 };
+  const docWithChecksum = addChecksum(doc);
+  const docWithoutChecksum = removeChecksum(docWithChecksum);
+
+  expect('_checksum' in docWithoutChecksum).toBeFalse();
+  expect(docWithoutChecksum.name).toEqual('John');
+  expect(docWithoutChecksum.age).toEqual(30);
+});
+
+tap.test('checksum: removeChecksum should handle document without checksum', async () => {
+  const doc = { name: 'John', age: 30 };
+  const result = removeChecksum(doc);
+
+  expect('_checksum' in result).toBeFalse();
+  expect(result.name).toEqual('John');
+  expect(result.age).toEqual(30);
+});
+
+// ============================================================================
+// Round-trip Tests
+// ============================================================================
+
+tap.test('checksum: full round-trip - add, verify, remove', async () => {
+  const original = { name: 'Test', value: 42, nested: { a: 1, b: 2 } };
+
+  // Add checksum
+  const withChecksum = addChecksum(original);
+  expect('_checksum' in withChecksum).toBeTrue();
+
+  // Verify checksum
+  expect(verifyChecksum(withChecksum)).toBeTrue();
+
+  // Remove checksum
+  const restored = removeChecksum(withChecksum);
+  expect('_checksum' in restored).toBeFalse();
+
+  // Original data should be intact
+  expect(restored.name).toEqual('Test');
+  expect(restored.value).toEqual(42);
+  expect(restored.nested.a).toEqual(1);
+  expect(restored.nested.b).toEqual(2);
+});
+
+export default tap.start();
diff --git a/test/test.tsmdb.indexengine.ts b/test/test.tsmdb.indexengine.ts
new file mode 100644
index 0000000..cc139ab
--- /dev/null
+++ b/test/test.tsmdb.indexengine.ts
@@ -0,0 +1,417 @@
+import { expect, tap } from '@git.zone/tstest/tapbundle';
+import * as smartmongo from '../ts/index.js';
+
+const { IndexEngine, MemoryStorageAdapter, ObjectId } = smartmongo.tsmdb;
+
+let storage: InstanceType<typeof MemoryStorageAdapter>;
+let indexEngine: InstanceType<typeof IndexEngine>;
+
+const TEST_DB = 'testdb';
+const TEST_COLL = 'indextest';
+
+// ============================================================================
+// Setup
+// ============================================================================
+
+tap.test('indexengine: should create IndexEngine instance', async () => {
+  storage = new MemoryStorageAdapter();
+  await storage.initialize();
+  await storage.createCollection(TEST_DB, TEST_COLL);
+
+  indexEngine = new IndexEngine(TEST_DB, TEST_COLL, storage);
+  expect(indexEngine).toBeTruthy();
+});
+
+// ============================================================================
+// Index Creation Tests
+// ============================================================================
+
+tap.test('indexengine: createIndex should create single-field index', async () => {
+  const indexName = await indexEngine.createIndex({ name: 1 });
+
+  expect(indexName).toEqual('name_1');
+
+  const exists = await indexEngine.indexExists('name_1');
+  expect(exists).toBeTrue();
+});
+
+tap.test('indexengine: createIndex should create compound index', async () => {
+  const indexName = await indexEngine.createIndex({ city: 1, state: -1 });
+
+  expect(indexName).toEqual('city_1_state_-1');
+
+  const exists = await indexEngine.indexExists('city_1_state_-1');
+  expect(exists).toBeTrue();
+});
+
+tap.test('indexengine: createIndex should use custom name if provided', async () => {
+  const indexName = await indexEngine.createIndex({ email: 1 }, { name: 'custom_email_index' });
+
+  expect(indexName).toEqual('custom_email_index');
+
+  const exists = await indexEngine.indexExists('custom_email_index');
+  expect(exists).toBeTrue();
+});
+
+tap.test('indexengine: createIndex should handle unique option', async () => {
+  const indexName = await indexEngine.createIndex({ uniqueField: 1 }, { unique: true });
+
+  expect(indexName).toEqual('uniqueField_1');
+
+  const indexes = await indexEngine.listIndexes();
+  const uniqueIndex = indexes.find(i => i.name === 'uniqueField_1');
+  expect(uniqueIndex!.unique).toBeTrue();
+});
+
+tap.test('indexengine: createIndex should handle sparse option', async () => {
+  const indexName = await indexEngine.createIndex({ sparseField: 1 }, { sparse: true });
+
+  expect(indexName).toEqual('sparseField_1');
+
+  const indexes = await indexEngine.listIndexes();
+  const sparseIndex = indexes.find(i => i.name === 'sparseField_1');
+  expect(sparseIndex!.sparse).toBeTrue();
+});
+
+tap.test('indexengine: createIndex should return existing index name if already exists', async () => {
+  const indexName1 = await indexEngine.createIndex({ existingField: 1 }, { name: 'existing_idx' });
+  const indexName2 = await indexEngine.createIndex({ existingField: 1 }, { name: 'existing_idx' });
+
+  expect(indexName1).toEqual(indexName2);
+});
+
+// ============================================================================
+// Index Listing and Existence Tests
+// ============================================================================
+
+tap.test('indexengine: listIndexes should return all indexes', async () => {
+  const indexes = await indexEngine.listIndexes();
+
+  expect(indexes.length).toBeGreaterThanOrEqual(5); // _id_ + created indexes
+  expect(indexes.some(i => i.name === '_id_')).toBeTrue();
+  expect(indexes.some(i => i.name === 'name_1')).toBeTrue();
+});
+
+tap.test('indexengine: indexExists should return true for existing index', async () => {
+  const exists = await indexEngine.indexExists('name_1');
+  expect(exists).toBeTrue();
+});
+
+tap.test('indexengine: indexExists should return false for non-existent index', async () => {
+  const exists = await indexEngine.indexExists('nonexistent_index');
+  expect(exists).toBeFalse();
+});
+
+// ============================================================================
+// Document Operations and Index Updates
+// ============================================================================
+
+tap.test('indexengine: should insert documents for index testing', async () => {
+  // Create a fresh index engine for document operations
+  await storage.dropCollection(TEST_DB, TEST_COLL);
+  await storage.createCollection(TEST_DB, TEST_COLL);
+
+  indexEngine = new IndexEngine(TEST_DB, TEST_COLL, storage);
+
+  // Create indexes first
+  await indexEngine.createIndex({ age: 1 });
+  await indexEngine.createIndex({ category: 1 });
+
+  // Insert test documents
+  const docs = [
+    { _id: new ObjectId(), name: 'Alice', age: 25, category: 'A' },
+    { _id: new ObjectId(), name: 'Bob', age: 30, category: 'B' },
+    { _id: new ObjectId(), name: 'Charlie', age: 35, category: 'A' },
+    { _id: new ObjectId(), name: 'Diana', age: 28, category: 'C' },
+    { _id: new ObjectId(), name: 'Eve', age: 30, category: 'B' },
+  ];
+
+  for (const doc of docs) {
+    const stored = await storage.insertOne(TEST_DB, TEST_COLL, doc);
+    await indexEngine.onInsert(stored);
+  }
+});
+
+tap.test('indexengine: onInsert should update indexes', async () => {
+  const newDoc = {
+    _id: new ObjectId(),
+    name: 'Frank',
+    age: 40,
+    category: 'D',
+  };
+
+  const stored = await storage.insertOne(TEST_DB, TEST_COLL, newDoc);
+  await indexEngine.onInsert(stored);
+
+  // Find by the indexed field
+  const candidates = await indexEngine.findCandidateIds({ age: 40 });
+  expect(candidates).toBeTruthy();
+  expect(candidates!.size).toEqual(1);
+});
+
+tap.test('indexengine: onUpdate should update indexes correctly', async () => {
+  // Get an existing document
+  const docs = await storage.findAll(TEST_DB, TEST_COLL);
+  const oldDoc = docs.find(d => d.name === 'Alice')!;
+
+  // Update the document
+  const newDoc = { ...oldDoc, age: 26 };
+  await storage.updateById(TEST_DB, TEST_COLL, oldDoc._id, newDoc);
+  await indexEngine.onUpdate(oldDoc, newDoc);
+
+  // Old value should not be in index
+  const oldCandidates = await indexEngine.findCandidateIds({ age: 25 });
+  expect(oldCandidates).toBeTruthy();
+  expect(oldCandidates!.has(oldDoc._id.toHexString())).toBeFalse();
+
+  // New value should be in index
+  const newCandidates = await indexEngine.findCandidateIds({ age: 26 });
+  expect(newCandidates).toBeTruthy();
+  expect(newCandidates!.has(oldDoc._id.toHexString())).toBeTrue();
+});
+
+tap.test('indexengine: onDelete should remove from indexes', async () => {
+  const docs = await storage.findAll(TEST_DB, TEST_COLL);
+  const docToDelete = docs.find(d => d.name === 'Frank')!;
+
+  await storage.deleteById(TEST_DB, TEST_COLL, docToDelete._id);
+  await indexEngine.onDelete(docToDelete);
+
+  const candidates = await indexEngine.findCandidateIds({ age: 40 });
+  expect(candidates).toBeTruthy();
+  expect(candidates!.has(docToDelete._id.toHexString())).toBeFalse();
+});
+
+// ============================================================================
+// findCandidateIds Tests
+// ============================================================================
+
+tap.test('indexengine: findCandidateIds with equality filter', async () => {
+  const candidates = await indexEngine.findCandidateIds({ age: 30 });
+
+  expect(candidates).toBeTruthy();
+  expect(candidates!.size).toEqual(2); // Bob and Eve both have age 30
+});
+
+tap.test('indexengine: findCandidateIds with $in filter', async () => {
+  const candidates = await indexEngine.findCandidateIds({ age: { $in: [28, 30] } });
+
+  expect(candidates).toBeTruthy();
+  expect(candidates!.size).toEqual(3); // Diana (28), Bob (30), Eve (30)
+});
+
+tap.test('indexengine: findCandidateIds with no matching index', async () => {
+  const candidates = await indexEngine.findCandidateIds({ nonIndexedField: 'value' });
+
+  // Should return null when no index can be used
+  expect(candidates).toBeNull();
+});
+
+tap.test('indexengine: findCandidateIds with empty filter', async () => {
+  const candidates = await indexEngine.findCandidateIds({});
+
+  // Empty filter = no index can be used
+  expect(candidates).toBeNull();
+});
+
+// ============================================================================
+// Range Query Tests (B-Tree)
+// ============================================================================
+
+tap.test('indexengine: findCandidateIds with $gt', async () => {
+  const candidates = await indexEngine.findCandidateIds({ age: { $gt: 30 } });
+
+  expect(candidates).toBeTruthy();
+  // Charlie (35) is > 30
+  expect(candidates!.size).toBeGreaterThanOrEqual(1);
+});
+
+tap.test('indexengine: findCandidateIds with $lt', async () => {
+  const candidates = await indexEngine.findCandidateIds({ age: { $lt: 28 } });
+
+  expect(candidates).toBeTruthy();
+  // Alice (26) is < 28
+  expect(candidates!.size).toBeGreaterThanOrEqual(1);
+});
+
+tap.test('indexengine: findCandidateIds with $gte', async () => {
+  const candidates = await indexEngine.findCandidateIds({ age: { $gte: 30 } });
+
+  expect(candidates).toBeTruthy();
+  // Bob (30), Eve (30), Charlie (35)
+  expect(candidates!.size).toBeGreaterThanOrEqual(3);
+});
+
+tap.test('indexengine: findCandidateIds with $lte', async () => {
+  const candidates = await indexEngine.findCandidateIds({ age: { $lte: 28 } });
+
+  expect(candidates).toBeTruthy();
+  // Alice (26), Diana (28)
+  expect(candidates!.size).toBeGreaterThanOrEqual(2);
+});
+
+tap.test('indexengine: findCandidateIds with range $gt and $lt', async () => {
+  const candidates = await indexEngine.findCandidateIds({ age: { $gt: 26, $lt: 35 } });
+
+  expect(candidates).toBeTruthy();
+  // Diana (28), Bob (30), Eve (30) are between 26 and 35 exclusive
+  expect(candidates!.size).toBeGreaterThanOrEqual(3);
+});
+
+// ============================================================================
+// Index Selection Tests
+// ============================================================================
+
+tap.test('indexengine: selectIndex should return best index for equality', async () => {
+  const result = indexEngine.selectIndex({ age: 30 });
+
+  expect(result).toBeTruthy();
+  expect(result!.name).toEqual('age_1');
+});
+
+tap.test('indexengine: selectIndex should return best index for range query', async () => {
+  const result = indexEngine.selectIndex({ age: { $gt: 25 } });
+
+  expect(result).toBeTruthy();
+  expect(result!.name).toEqual('age_1');
+});
+
+tap.test('indexengine: selectIndex should return null for no matching filter', async () => {
+  const result = indexEngine.selectIndex({ nonIndexedField: 'value' });
+
+  expect(result).toBeNull();
+});
+
+tap.test('indexengine: selectIndex should return null for empty filter', async () => {
+  const result = indexEngine.selectIndex({});
+
+  expect(result).toBeNull();
+});
+
+tap.test('indexengine: selectIndex should prefer more specific indexes', async () => {
+  // Create a compound index
+  await indexEngine.createIndex({ age: 1, category: 1 }, { name: 'age_category_compound' });
+
+  // Query that matches compound index
+  const result = indexEngine.selectIndex({ age: 30, category: 'B' });
+
+  expect(result).toBeTruthy();
+  // Should prefer the compound index since it covers more fields
+  expect(result!.name).toEqual('age_category_compound');
+});
+
+// ============================================================================
+// Drop Index Tests
+// ============================================================================
+
+tap.test('indexengine: dropIndex should remove the index', async () => {
+  await indexEngine.createIndex({ dropTest: 1 }, { name: 'drop_test_idx' });
+  expect(await indexEngine.indexExists('drop_test_idx')).toBeTrue();
+
+  await indexEngine.dropIndex('drop_test_idx');
+  expect(await indexEngine.indexExists('drop_test_idx')).toBeFalse();
+});
+
+tap.test('indexengine: dropIndex should throw for _id index', async () => {
+  let threw = false;
+  try {
+    await indexEngine.dropIndex('_id_');
+  } catch (e) {
+    threw = true;
+  }
+  expect(threw).toBeTrue();
+});
+
+tap.test('indexengine: dropIndex should throw for non-existent index', async () => {
+  let threw = false;
+  try {
+    await indexEngine.dropIndex('nonexistent_index');
+  } catch (e) {
+    threw = true;
+  }
+  expect(threw).toBeTrue();
+});
+
+tap.test('indexengine: dropAllIndexes should remove all indexes except _id', async () => {
+  // Create some indexes to drop
+  await indexEngine.createIndex({ toDrop1: 1 });
+  await indexEngine.createIndex({ toDrop2: 1 });
+
+  await indexEngine.dropAllIndexes();
+
+  const indexes = await indexEngine.listIndexes();
+  expect(indexes.length).toEqual(1);
+  expect(indexes[0].name).toEqual('_id_');
+});
+
+// ============================================================================
+// Unique Index Constraint Tests
+// ============================================================================
+
+tap.test('indexengine: unique index should prevent duplicate inserts', async () => {
+  // Create fresh collection
+  await storage.dropCollection(TEST_DB, 'uniquetest');
+  await storage.createCollection(TEST_DB, 'uniquetest');
+
+  const uniqueIndexEngine = new IndexEngine(TEST_DB, 'uniquetest', storage);
+  await uniqueIndexEngine.createIndex({ email: 1 }, { unique: true });
+
+  // Insert first document
+  const doc1 = { _id: new ObjectId(), email: 'test@example.com', name: 'Test' };
+  const stored1 = await storage.insertOne(TEST_DB, 'uniquetest', doc1);
+  await uniqueIndexEngine.onInsert(stored1);
+
+  // Try to insert duplicate
+  const doc2 = { _id: new ObjectId(), email: 'test@example.com', name: 'Test2' };
+  const stored2 = await storage.insertOne(TEST_DB, 'uniquetest', doc2);
+
+  let threw = false;
+  try {
+    await uniqueIndexEngine.onInsert(stored2);
+  } catch (e: any) {
+    threw = true;
+    expect(e.message).toContain('duplicate key');
+  }
+
+  expect(threw).toBeTrue();
+});
+
+// ============================================================================
+// Sparse Index Tests
+// ============================================================================
+
+tap.test('indexengine: sparse index should not include documents without the field', async () => {
+  // Create fresh collection
+  await storage.dropCollection(TEST_DB, 'sparsetest');
+  await storage.createCollection(TEST_DB, 'sparsetest');
+
+  const sparseIndexEngine = new IndexEngine(TEST_DB, 'sparsetest', storage);
+  await sparseIndexEngine.createIndex({ optionalField: 1 }, { sparse: true });
+
+  // Insert doc with the field
+  const doc1 = { _id: new ObjectId(), optionalField: 'hasValue', name: 'HasField' };
+  const stored1 = await storage.insertOne(TEST_DB, 'sparsetest', doc1);
+  await sparseIndexEngine.onInsert(stored1);
+
+  // Insert doc without the field
+  const doc2 = { _id: new ObjectId(), name: 'NoField' };
+  const stored2 = await storage.insertOne(TEST_DB, 'sparsetest', doc2);
+  await sparseIndexEngine.onInsert(stored2);
+
+  // Search for documents with the field
+  const candidates = await sparseIndexEngine.findCandidateIds({ optionalField: 'hasValue' });
+  expect(candidates).toBeTruthy();
+  expect(candidates!.size).toEqual(1);
+  expect(candidates!.has(stored1._id.toHexString())).toBeTrue();
+});
+
+// ============================================================================
+// Cleanup
+// ============================================================================
+
+tap.test('indexengine: cleanup', async () => {
+  await storage.close();
+  expect(true).toBeTrue();
+});
+
+export default tap.start();
diff --git a/test/test.tsmdb.queryplanner.ts b/test/test.tsmdb.queryplanner.ts
new file mode 100644
index 0000000..b65ae07
--- /dev/null
+++ b/test/test.tsmdb.queryplanner.ts
@@ -0,0 +1,273 @@
+import { expect, tap } from '@git.zone/tstest/tapbundle';
+import * as smartmongo from '../ts/index.js';
+
+const { QueryPlanner, IndexEngine, MemoryStorageAdapter, ObjectId } = smartmongo.tsmdb;
+
+let storage: InstanceType<typeof MemoryStorageAdapter>;
+let indexEngine: InstanceType<typeof IndexEngine>;
+let queryPlanner: InstanceType<typeof QueryPlanner>;
+
+const TEST_DB = 'testdb';
+const TEST_COLL = 'testcoll';
+
+// ============================================================================
+// Setup
+// ============================================================================
+
+tap.test('queryplanner: should create QueryPlanner instance', async () => {
+  storage = new MemoryStorageAdapter();
+  await storage.initialize();
+  await storage.createCollection(TEST_DB, TEST_COLL);
+
+  indexEngine = new IndexEngine(TEST_DB, TEST_COLL, storage);
+  queryPlanner = new QueryPlanner(indexEngine);
+
+  expect(queryPlanner).toBeTruthy();
+});
+
+tap.test('queryplanner: should insert test documents', async () => {
+  // Insert test documents
+  const docs = [
+    { _id: new ObjectId(), name: 'Alice', age: 25, city: 'NYC', category: 'A' },
+    { _id: new ObjectId(), name: 'Bob', age: 30, city: 'LA', category: 'B' },
+    { _id: new ObjectId(), name: 'Charlie', age: 35, city: 'NYC', category: 'A' },
+    { _id: new ObjectId(), name: 'Diana', age: 28, city: 'Chicago', category: 'C' },
+    { _id: new ObjectId(), name: 'Eve', age: 32, city: 'LA', category: 'B' },
+  ];
+
+  for (const doc of docs) {
+    await storage.insertOne(TEST_DB, TEST_COLL, doc);
+  }
+});
+
+// ============================================================================
+// Basic Plan Tests
+// ============================================================================
+
+tap.test('queryplanner: empty filter should result in COLLSCAN', async () => {
+  const plan = await queryPlanner.plan({});
+
+  expect(plan.type).toEqual('COLLSCAN');
+  expect(plan.indexCovering).toBeFalse();
+  expect(plan.selectivity).toEqual(1.0);
+  expect(plan.explanation).toContain('No filter');
+});
+
+tap.test('queryplanner: null filter should result in COLLSCAN', async () => {
+  const plan = await queryPlanner.plan(null as any);
+
+  expect(plan.type).toEqual('COLLSCAN');
+});
+
+tap.test('queryplanner: filter with no matching index should result in COLLSCAN', async () => {
+  const plan = await queryPlanner.plan({ nonExistentField: 'value' });
+
+  expect(plan.type).toEqual('COLLSCAN');
+  expect(plan.explanation).toContain('No suitable index');
+});
+
+// ============================================================================
+// Index Scan Tests (with indexes)
+// ============================================================================
+
+tap.test('queryplanner: should create test indexes', async () => {
+  await indexEngine.createIndex({ age: 1 }, { name: 'age_1' });
+  await indexEngine.createIndex({ name: 1 }, { name: 'name_1' });
+  await indexEngine.createIndex({ city: 1, category: 1 }, { name: 'city_category_1' });
+
+  const indexes = await indexEngine.listIndexes();
+  expect(indexes.length).toBeGreaterThanOrEqual(4); // _id_ + 3 created
+});
+
+tap.test('queryplanner: simple equality filter should use IXSCAN', async () => {
+  const plan = await queryPlanner.plan({ age: 30 });
+
+  expect(plan.type).toEqual('IXSCAN');
+  expect(plan.indexName).toEqual('age_1');
+  expect(plan.indexFieldsUsed).toContain('age');
+  expect(plan.usesRange).toBeFalse();
+});
+
+tap.test('queryplanner: $eq operator should use IXSCAN', async () => {
+  const plan = await queryPlanner.plan({ name: { $eq: 'Alice' } });
+
+  expect(plan.type).toEqual('IXSCAN');
+  expect(plan.indexName).toEqual('name_1');
+  expect(plan.indexFieldsUsed).toContain('name');
+});
+
+tap.test('queryplanner: range filter ($gt) should use IXSCAN_RANGE', async () => {
+  const plan = await queryPlanner.plan({ age: { $gt: 25 } });
+
+  expect(plan.type).toEqual('IXSCAN_RANGE');
+  expect(plan.indexName).toEqual('age_1');
+  expect(plan.usesRange).toBeTrue();
+});
+
+tap.test('queryplanner: range filter ($lt) should use IXSCAN_RANGE', async () => {
+  const plan = await queryPlanner.plan({ age: { $lt: 35 } });
+
+  expect(plan.type).toEqual('IXSCAN_RANGE');
+  expect(plan.usesRange).toBeTrue();
+});
+
+tap.test('queryplanner: range filter ($gte, $lte) should use IXSCAN_RANGE', async () => {
+  const plan = await queryPlanner.plan({ age: { $gte: 25, $lte: 35 } });
+
+  expect(plan.type).toEqual('IXSCAN_RANGE');
+  expect(plan.usesRange).toBeTrue();
+});
+
+tap.test('queryplanner: $in operator should use IXSCAN', async () => {
+  const plan = await queryPlanner.plan({ age: { $in: [25, 30, 35] } });
+
+  expect(plan.type).toEqual('IXSCAN');
+  expect(plan.indexName).toEqual('age_1');
+});
+
+// ============================================================================
+// Compound Index Tests
+// ============================================================================
+
+tap.test('queryplanner: compound index - first field equality should use index', async () => {
+  const plan = await queryPlanner.plan({ city: 'NYC' });
+
+  expect(plan.type).toEqual('IXSCAN');
+  expect(plan.indexName).toEqual('city_category_1');
+  expect(plan.indexFieldsUsed).toContain('city');
+});
+
+tap.test('queryplanner: compound index - both fields should use full index', async () => {
+  const plan = await queryPlanner.plan({ city: 'NYC', category: 'A' });
+
+  expect(plan.type).toEqual('IXSCAN');
+  expect(plan.indexName).toEqual('city_category_1');
+  expect(plan.indexFieldsUsed).toContain('city');
+  expect(plan.indexFieldsUsed).toContain('category');
+  expect(plan.indexFieldsUsed.length).toEqual(2);
+});
+
+// ============================================================================
+// Selectivity Tests
+// ============================================================================
+
+tap.test('queryplanner: equality query should have low selectivity', async () => {
+  const plan = await queryPlanner.plan({ age: 30 });
+
+  expect(plan.selectivity).toBeLessThan(0.1);
+});
+
+tap.test('queryplanner: range query should have moderate selectivity', async () => {
+  const plan = await queryPlanner.plan({ age: { $gt: 25 } });
+
+  expect(plan.selectivity).toBeGreaterThan(0);
+  expect(plan.selectivity).toBeLessThan(1);
+});
+
+tap.test('queryplanner: $in query selectivity depends on array size', async () => {
+  const smallInPlan = await queryPlanner.plan({ age: { $in: [25] } });
+  const largeInPlan = await queryPlanner.plan({ age: { $in: [25, 26, 27, 28, 29, 30] } });
+
+  // Larger $in should have higher selectivity (less selective = more documents)
+  expect(largeInPlan.selectivity).toBeGreaterThanOrEqual(smallInPlan.selectivity);
+});
+
+// ============================================================================
+// Index Covering Tests
+// ============================================================================
+
+tap.test('queryplanner: query covering all filter fields should be index covering', async () => {
+  const plan = await queryPlanner.plan({ age: 30 });
+
+  // All filter fields are covered by the index
+  expect(plan.indexCovering).toBeTrue();
+});
+
+tap.test('queryplanner: query with residual filter should not be index covering', async () => {
+  const plan = await queryPlanner.plan({ city: 'NYC', name: 'Alice' });
+
+  // 'name' is not in the compound index city_category, so it's residual
+  expect(plan.indexCovering).toBeFalse();
+  expect(plan.residualFilter).toBeTruthy();
+});
+
+// ============================================================================
+// Explain Tests
+// ============================================================================
+
+tap.test('queryplanner: explain should return detailed plan info', async () => {
+  const explanation = await queryPlanner.explain({ age: 30 });
+
+  expect(explanation.queryPlanner).toBeTruthy();
+  expect(explanation.queryPlanner.plannerVersion).toEqual(1);
+  expect(explanation.queryPlanner.winningPlan).toBeTruthy();
+  expect(explanation.queryPlanner.rejectedPlans).toBeArray();
+});
+
+tap.test('queryplanner: explain should include winning and rejected plans', async () => {
+  const explanation = await queryPlanner.explain({ age: 30 });
+
+  expect(explanation.queryPlanner.winningPlan.type).toBeTruthy();
+  expect(explanation.queryPlanner.rejectedPlans.length).toBeGreaterThan(0);
+});
+
+tap.test('queryplanner: explain winning plan should be the best plan', async () => {
+  const explanation = await queryPlanner.explain({ age: 30 });
+
+  // Winning plan should use an index, not collection scan (if index exists)
+  expect(explanation.queryPlanner.winningPlan.type).toEqual('IXSCAN');
+
+  // There should be a COLLSCAN in rejected plans
+  const hasCOLLSCAN = explanation.queryPlanner.rejectedPlans.some(p => p.type === 'COLLSCAN');
+  expect(hasCOLLSCAN).toBeTrue();
+});
+
+// ============================================================================
+// $and Operator Tests
+// ============================================================================
+
+tap.test('queryplanner: $and conditions should be analyzed', async () => {
+  const plan = await queryPlanner.plan({
+    $and: [
+      { age: { $gte: 25 } },
+      { age: { $lte: 35 } },
+    ],
+  });
+
+  expect(plan.type).toEqual('IXSCAN_RANGE');
+  expect(plan.indexName).toEqual('age_1');
+});
+
+// ============================================================================
+// Edge Cases
+// ============================================================================
+
+tap.test('queryplanner: should handle complex nested operators', async () => {
+  const plan = await queryPlanner.plan({
+    age: { $gte: 20, $lte: 40 },
+    city: 'NYC',
+  });
+
+  expect(plan).toBeTruthy();
+  expect(plan.type).not.toBeUndefined();
+});
+
+tap.test('queryplanner: should handle $exists operator', async () => {
+  await indexEngine.createIndex({ email: 1 }, { name: 'email_1', sparse: true });
+
+  const plan = await queryPlanner.plan({ email: { $exists: true } });
+
+  // $exists can use sparse indexes
+  expect(plan).toBeTruthy();
+});
+
+// ============================================================================
+// Cleanup
+// ============================================================================
+
+tap.test('queryplanner: cleanup', async () => {
+  await storage.close();
+  expect(true).toBeTrue();
+});
+
+export default tap.start();
diff --git a/test/test.tsmdb.session.ts b/test/test.tsmdb.session.ts
new file mode 100644
index 0000000..3cc24cf
--- /dev/null
+++ b/test/test.tsmdb.session.ts
@@ -0,0 +1,361 @@
+import { expect, tap } from '@git.zone/tstest/tapbundle';
+import * as smartmongo from '../ts/index.js';
+
+const { SessionEngine } = smartmongo.tsmdb;
+
+let sessionEngine: InstanceType<typeof SessionEngine>;
+
+// ============================================================================
+// Setup
+// ============================================================================
+
+tap.test('session: should create SessionEngine instance', async () => {
+  sessionEngine = new SessionEngine({
+    sessionTimeoutMs: 1000, // 1 second for testing
+    cleanupIntervalMs: 10000, // 10 seconds to avoid cleanup during tests
+  });
+  expect(sessionEngine).toBeTruthy();
+});
+
+// ============================================================================
+// Session Lifecycle Tests
+// ============================================================================
+
+tap.test('session: startSession should create session with auto-generated ID', async () => {
+  const session = sessionEngine.startSession();
+
+  expect(session).toBeTruthy();
+  expect(session.id).toBeTruthy();
+  expect(session.id.length).toBeGreaterThanOrEqual(32); // UUID hex string (32 or 36 with hyphens)
+  expect(session.createdAt).toBeGreaterThan(0);
+  expect(session.lastActivityAt).toBeGreaterThan(0);
+  expect(session.inTransaction).toBeFalse();
+});
+
+tap.test('session: startSession should create session with specified ID', async () => {
+  const customId = 'custom-session-id-12345';
+  const session = sessionEngine.startSession(customId);
+
+  expect(session.id).toEqual(customId);
+});
+
+tap.test('session: startSession should create session with metadata', async () => {
+  const metadata = { client: 'test-client', version: '1.0' };
+  const session = sessionEngine.startSession(undefined, metadata);
+
+  expect(session.metadata).toBeTruthy();
+  expect(session.metadata!.client).toEqual('test-client');
+  expect(session.metadata!.version).toEqual('1.0');
+});
+
+tap.test('session: getSession should return session by ID', async () => {
+  const created = sessionEngine.startSession('get-session-test');
+  const retrieved = sessionEngine.getSession('get-session-test');
+
+  expect(retrieved).toBeTruthy();
+  expect(retrieved!.id).toEqual('get-session-test');
+  expect(retrieved!.id).toEqual(created.id);
+});
+
+tap.test('session: getSession should return undefined for non-existent session', async () => {
+  const session = sessionEngine.getSession('non-existent-session-id');
+  expect(session).toBeUndefined();
+});
+
+tap.test('session: touchSession should update lastActivityAt', async () => {
+  const session = sessionEngine.startSession('touch-test-session');
+  const originalLastActivity = session.lastActivityAt;
+
+  // Wait a bit to ensure time difference
+  await new Promise(resolve => setTimeout(resolve, 10));
+
+  const touched = sessionEngine.touchSession('touch-test-session');
+  expect(touched).toBeTrue();
+
+  const updated = sessionEngine.getSession('touch-test-session');
+  expect(updated!.lastActivityAt).toBeGreaterThanOrEqual(originalLastActivity);
+});
+
+tap.test('session: touchSession should return false for non-existent session', async () => {
+  const touched = sessionEngine.touchSession('non-existent-touch-session');
+  expect(touched).toBeFalse();
+});
+
+tap.test('session: endSession should remove the session', async () => {
+  sessionEngine.startSession('end-session-test');
+  expect(sessionEngine.getSession('end-session-test')).toBeTruthy();
+
+  const ended = await sessionEngine.endSession('end-session-test');
+  expect(ended).toBeTrue();
+
+  expect(sessionEngine.getSession('end-session-test')).toBeUndefined();
+});
+
+tap.test('session: endSession should return false for non-existent session', async () => {
+  const ended = await sessionEngine.endSession('non-existent-end-session');
+  expect(ended).toBeFalse();
+});
+
+// ============================================================================
+// Session Expiry Tests
+// ============================================================================
+
+tap.test('session: isSessionExpired should return false for fresh session', async () => {
+  const session = sessionEngine.startSession('fresh-session');
+  const isExpired = sessionEngine.isSessionExpired(session);
+  expect(isExpired).toBeFalse();
+});
+
+tap.test('session: isSessionExpired should return true for old session', async () => {
+  // Create a session with old lastActivityAt
+  const session = sessionEngine.startSession('old-session');
+  // Manually set lastActivityAt to old value (sessionTimeoutMs is 1000ms)
+  (session as any).lastActivityAt = Date.now() - 2000;
+
+  const isExpired = sessionEngine.isSessionExpired(session);
+  expect(isExpired).toBeTrue();
+});
+
+tap.test('session: getSession should return undefined for expired session', async () => {
+  const session = sessionEngine.startSession('expiring-session');
+  // Manually expire the session
+  (session as any).lastActivityAt = Date.now() - 2000;
+
+  const retrieved = sessionEngine.getSession('expiring-session');
+  expect(retrieved).toBeUndefined();
+});
+
+// ============================================================================
+// Transaction Integration Tests
+// ============================================================================
+
+tap.test('session: startTransaction should mark session as in transaction', async () => {
+  sessionEngine.startSession('txn-session-1');
+  const started = sessionEngine.startTransaction('txn-session-1', 'txn-id-1', 1);
+
+  expect(started).toBeTrue();
+
+  const session = sessionEngine.getSession('txn-session-1');
+  expect(session!.inTransaction).toBeTrue();
+  expect(session!.txnId).toEqual('txn-id-1');
+  expect(session!.txnNumber).toEqual(1);
+});
+
+tap.test('session: startTransaction should return false for non-existent session', async () => {
+  const started = sessionEngine.startTransaction('non-existent-txn-session', 'txn-id');
+  expect(started).toBeFalse();
+});
+
+tap.test('session: endTransaction should clear transaction state', async () => {
+  sessionEngine.startSession('txn-session-2');
+  sessionEngine.startTransaction('txn-session-2', 'txn-id-2');
+
+  const ended = sessionEngine.endTransaction('txn-session-2');
+  expect(ended).toBeTrue();
+
+  const session = sessionEngine.getSession('txn-session-2');
+  expect(session!.inTransaction).toBeFalse();
+  expect(session!.txnId).toBeUndefined();
+  expect(session!.txnNumber).toBeUndefined();
+});
+
+tap.test('session: endTransaction should return false for non-existent session', async () => {
+  const ended = sessionEngine.endTransaction('non-existent-end-txn-session');
+  expect(ended).toBeFalse();
+});
+
+tap.test('session: getTransactionId should return transaction ID', async () => {
+  sessionEngine.startSession('txn-id-session');
+  sessionEngine.startTransaction('txn-id-session', 'my-txn-id');
+
+  const txnId = sessionEngine.getTransactionId('txn-id-session');
+  expect(txnId).toEqual('my-txn-id');
+});
+
+tap.test('session: getTransactionId should return undefined for session without transaction', async () => {
+  sessionEngine.startSession('no-txn-session');
+  const txnId = sessionEngine.getTransactionId('no-txn-session');
+  expect(txnId).toBeUndefined();
+});
+
+tap.test('session: getTransactionId should return undefined for non-existent session', async () => {
+  const txnId = sessionEngine.getTransactionId('non-existent-txn-id-session');
+  expect(txnId).toBeUndefined();
+});
+
+tap.test('session: isInTransaction should return correct state', async () => {
+  sessionEngine.startSession('in-txn-check-session');
+
+  expect(sessionEngine.isInTransaction('in-txn-check-session')).toBeFalse();
+
+  sessionEngine.startTransaction('in-txn-check-session', 'txn-check');
+  expect(sessionEngine.isInTransaction('in-txn-check-session')).toBeTrue();
+
+  sessionEngine.endTransaction('in-txn-check-session');
+  expect(sessionEngine.isInTransaction('in-txn-check-session')).toBeFalse();
+});
+
+tap.test('session: isInTransaction should return false for non-existent session', async () => {
+  expect(sessionEngine.isInTransaction('non-existent-in-txn-session')).toBeFalse();
+});
+
+// ============================================================================
+// Session Listing Tests
+// ============================================================================
+
+tap.test('session: listSessions should return all active sessions', async () => {
+  // Close and recreate to have a clean slate
+  sessionEngine.close();
+  sessionEngine = new SessionEngine({
+    sessionTimeoutMs: 10000,
+    cleanupIntervalMs: 60000,
+  });
+
+  sessionEngine.startSession('list-session-1');
+  sessionEngine.startSession('list-session-2');
+  sessionEngine.startSession('list-session-3');
+
+  const sessions = sessionEngine.listSessions();
+  expect(sessions.length).toEqual(3);
+});
+
+tap.test('session: listSessions should not include expired sessions', async () => {
+  const session = sessionEngine.startSession('expired-list-session');
+  // Expire the session
+  (session as any).lastActivityAt = Date.now() - 20000;
+
+  const sessions = sessionEngine.listSessions();
+  const found = sessions.find(s => s.id === 'expired-list-session');
+  expect(found).toBeUndefined();
+});
+
+tap.test('session: getSessionCount should return correct count', async () => {
+  const count = sessionEngine.getSessionCount();
+  expect(count).toBeGreaterThanOrEqual(3); // We created 3 sessions above
+});
+
+tap.test('session: getSessionsWithTransactions should filter correctly', async () => {
+  // Clean slate
+  sessionEngine.close();
+  sessionEngine = new SessionEngine({
+    sessionTimeoutMs: 10000,
+    cleanupIntervalMs: 60000,
+  });
+
+  sessionEngine.startSession('no-txn-1');
+  sessionEngine.startSession('no-txn-2');
+  sessionEngine.startSession('with-txn-1');
+  sessionEngine.startSession('with-txn-2');
+
+  sessionEngine.startTransaction('with-txn-1', 'txn-a');
+  sessionEngine.startTransaction('with-txn-2', 'txn-b');
+
+  const txnSessions = sessionEngine.getSessionsWithTransactions();
+  expect(txnSessions.length).toEqual(2);
+  expect(txnSessions.every(s => s.inTransaction)).toBeTrue();
+});
+
+// ============================================================================
+// getOrCreateSession Tests
+// ============================================================================
+
+tap.test('session: getOrCreateSession should create if missing', async () => {
+  const session = sessionEngine.getOrCreateSession('get-or-create-new');
+  expect(session).toBeTruthy();
+  expect(session.id).toEqual('get-or-create-new');
+});
+
+tap.test('session: getOrCreateSession should return existing session', async () => {
+  const created = sessionEngine.startSession('get-or-create-existing');
+  const retrieved = sessionEngine.getOrCreateSession('get-or-create-existing');
+
+  expect(retrieved.id).toEqual(created.id);
+  expect(retrieved.createdAt).toEqual(created.createdAt);
+});
+
+tap.test('session: getOrCreateSession should touch existing session', async () => {
+  const session = sessionEngine.startSession('get-or-create-touch');
+  const originalLastActivity = session.lastActivityAt;
+
+  await new Promise(resolve => setTimeout(resolve, 10));
+
+  sessionEngine.getOrCreateSession('get-or-create-touch');
+  const updated = sessionEngine.getSession('get-or-create-touch');
+
+  expect(updated!.lastActivityAt).toBeGreaterThanOrEqual(originalLastActivity);
+});
+
+// ============================================================================
+// extractSessionId Static Method Tests
+// ============================================================================
+
+tap.test('session: extractSessionId should handle UUID object', async () => {
+  const { ObjectId } = smartmongo.tsmdb;
+  const uuid = new smartmongo.tsmdb.plugins.bson.UUID();
+  const lsid = { id: uuid };
+
+  const extracted = SessionEngine.extractSessionId(lsid);
+  expect(extracted).toEqual(uuid.toHexString());
+});
+
+tap.test('session: extractSessionId should handle string ID', async () => {
+  const lsid = { id: 'string-session-id' };
+
+  const extracted = SessionEngine.extractSessionId(lsid);
+  expect(extracted).toEqual('string-session-id');
+});
+
+tap.test('session: extractSessionId should handle binary format', async () => {
+  const binaryData = Buffer.from('test-binary-uuid', 'utf8').toString('base64');
+  const lsid = { id: { $binary: { base64: binaryData } } };
+
+  const extracted = SessionEngine.extractSessionId(lsid);
+  expect(extracted).toBeTruthy();
+  expect(typeof extracted).toEqual('string');
+});
+
+tap.test('session: extractSessionId should return undefined for null/undefined', async () => {
+  expect(SessionEngine.extractSessionId(null)).toBeUndefined();
+  expect(SessionEngine.extractSessionId(undefined)).toBeUndefined();
+});
+
+tap.test('session: extractSessionId should return undefined for empty object', async () => {
+  expect(SessionEngine.extractSessionId({})).toBeUndefined();
+});
+
+// ============================================================================
+// refreshSession Tests
+// ============================================================================
+
+tap.test('session: refreshSession should update lastActivityAt', async () => {
+  const session = sessionEngine.startSession('refresh-session-test');
+  const originalLastActivity = session.lastActivityAt;
+
+  await new Promise(resolve => setTimeout(resolve, 10));
+
+  const refreshed = sessionEngine.refreshSession('refresh-session-test');
+  expect(refreshed).toBeTrue();
+
+  const updated = sessionEngine.getSession('refresh-session-test');
+  expect(updated!.lastActivityAt).toBeGreaterThanOrEqual(originalLastActivity);
+});
+
+tap.test('session: refreshSession should return false for non-existent session', async () => {
+  const refreshed = sessionEngine.refreshSession('non-existent-refresh-session');
+  expect(refreshed).toBeFalse();
+});
+
+// ============================================================================
+// Cleanup
+// ============================================================================
+
+tap.test('session: close should clear all sessions', async () => {
+  sessionEngine.startSession('close-test-session');
+  expect(sessionEngine.getSessionCount()).toBeGreaterThan(0);
+
+  sessionEngine.close();
+
+  expect(sessionEngine.getSessionCount()).toEqual(0);
+});
+
+export default tap.start();
diff --git a/test/test.tsmdb.wal.ts b/test/test.tsmdb.wal.ts
new file mode 100644
index 0000000..3d304b0
--- /dev/null
+++ b/test/test.tsmdb.wal.ts
@@ -0,0 +1,411 @@
+import { expect, tap } from '@git.zone/tstest/tapbundle';
+import * as smartmongo from '../ts/index.js';
+import * as path from 'path';
+import * as fs from 'fs/promises';
+
+const { WAL, ObjectId } = smartmongo.tsmdb;
+
+let wal: InstanceType<typeof WAL>;
+const TEST_WAL_PATH = '/tmp/tsmdb-test-wal/test.wal';
+
+// Helper to clean up test files
+async function cleanupTestFiles() {
+  try {
+    await fs.rm('/tmp/tsmdb-test-wal', { recursive: true, force: true });
+  } catch {
+    // Ignore if doesn't exist
+  }
+}
+
+// ============================================================================
+// Setup
+// ============================================================================
+
+tap.test('wal: cleanup before tests', async () => {
+  await cleanupTestFiles();
+});
+
+tap.test('wal: should create WAL instance', async () => {
+  wal = new WAL(TEST_WAL_PATH, { checkpointInterval: 100 });
+  expect(wal).toBeTruthy();
+});
+
+tap.test('wal: should initialize WAL', async () => {
+  const result = await wal.initialize();
+  expect(result).toBeTruthy();
+  expect(result.recoveredEntries).toBeArray();
+  expect(result.recoveredEntries.length).toEqual(0);
+});
+
+// ============================================================================
+// LSN Tests
+// ============================================================================
+
+tap.test('wal: getCurrentLsn should return 0 initially', async () => {
+  const lsn = wal.getCurrentLsn();
+  expect(lsn).toEqual(0);
+});
+
+tap.test('wal: LSN should increment after logging', async () => {
+  const doc = { _id: new ObjectId(), name: 'Test' };
+  const lsn = await wal.logInsert('testdb', 'testcoll', doc as any);
+
+  expect(lsn).toEqual(1);
+  expect(wal.getCurrentLsn()).toEqual(1);
+});
+
+// ============================================================================
+// Insert Logging Tests
+// ============================================================================
+
+tap.test('wal: logInsert should create entry with correct structure', async () => {
+  const doc = { _id: new ObjectId(), name: 'InsertTest', value: 42 };
+  const lsn = await wal.logInsert('testdb', 'insertcoll', doc as any);
+
+  expect(lsn).toBeGreaterThan(0);
+
+  const entries = wal.getEntriesAfter(lsn - 1);
+  const entry = entries.find(e => e.lsn === lsn);
+
+  expect(entry).toBeTruthy();
+  expect(entry!.operation).toEqual('insert');
+  expect(entry!.dbName).toEqual('testdb');
+  expect(entry!.collName).toEqual('insertcoll');
+  expect(entry!.documentId).toEqual(doc._id.toHexString());
+  expect(entry!.data).toBeTruthy();
+  expect(entry!.timestamp).toBeGreaterThan(0);
+  expect(entry!.checksum).toBeGreaterThan(0);
+});
+
+tap.test('wal: logInsert with transaction ID', async () => {
+  const doc = { _id: new ObjectId(), name: 'TxnInsertTest' };
+  const lsn = await wal.logInsert('testdb', 'insertcoll', doc as any, 'txn-123');
+
+  const entries = wal.getEntriesAfter(lsn - 1);
+  const entry = entries.find(e => e.lsn === lsn);
+
+  expect(entry!.txnId).toEqual('txn-123');
+});
+
+// ============================================================================
+// Update Logging Tests
+// ============================================================================
+
+tap.test('wal: logUpdate should store old and new document', async () => {
+  const oldDoc = { _id: new ObjectId(), name: 'OldName', value: 1 };
+  const newDoc = { ...oldDoc, name: 'NewName', value: 2 };
+
+  const lsn = await wal.logUpdate('testdb', 'updatecoll', oldDoc as any, newDoc as any);
+
+  const entries = wal.getEntriesAfter(lsn - 1);
+  const entry = entries.find(e => e.lsn === lsn);
+
+  expect(entry).toBeTruthy();
+  expect(entry!.operation).toEqual('update');
+  expect(entry!.data).toBeTruthy();
+  expect(entry!.previousData).toBeTruthy();
+  expect(entry!.documentId).toEqual(oldDoc._id.toHexString());
+});
+
+// ============================================================================
+// Delete Logging Tests
+// ============================================================================
+
+tap.test('wal: logDelete should record deleted document', async () => {
+  const doc = { _id: new ObjectId(), name: 'ToDelete' };
+
+  const lsn = await wal.logDelete('testdb', 'deletecoll', doc as any);
+
+  const entries = wal.getEntriesAfter(lsn - 1);
+  const entry = entries.find(e => e.lsn === lsn);
+
+  expect(entry).toBeTruthy();
+  expect(entry!.operation).toEqual('delete');
+  expect(entry!.previousData).toBeTruthy();
+  expect(entry!.data).toBeUndefined();
+});
+
+// ============================================================================
+// Transaction Logging Tests
+// ============================================================================
+
+tap.test('wal: logBeginTransaction should create begin entry', async () => {
+  const lsn = await wal.logBeginTransaction('txn-begin-test');
+
+  const entries = wal.getEntriesAfter(lsn - 1);
+  const entry = entries.find(e => e.lsn === lsn);
+
+  expect(entry).toBeTruthy();
+  expect(entry!.operation).toEqual('begin');
+  expect(entry!.txnId).toEqual('txn-begin-test');
+});
+
+tap.test('wal: logCommitTransaction should create commit entry', async () => {
+  const lsn = await wal.logCommitTransaction('txn-commit-test');
+
+  const entries = wal.getEntriesAfter(lsn - 1);
+  const entry = entries.find(e => e.lsn === lsn);
+
+  expect(entry).toBeTruthy();
+  expect(entry!.operation).toEqual('commit');
+  expect(entry!.txnId).toEqual('txn-commit-test');
+});
+
+tap.test('wal: logAbortTransaction should create abort entry', async () => {
+  const lsn = await wal.logAbortTransaction('txn-abort-test');
+
+  const entries = wal.getEntriesAfter(lsn - 1);
+  const entry = entries.find(e => e.lsn === lsn);
+
+  expect(entry).toBeTruthy();
+  expect(entry!.operation).toEqual('abort');
+  expect(entry!.txnId).toEqual('txn-abort-test');
+});
+
+// ============================================================================
+// getTransactionEntries Tests
+// ============================================================================
+
+tap.test('wal: getTransactionEntries should return entries for transaction', async () => {
+  // Log a complete transaction
+  const txnId = 'txn-entries-test';
+  await wal.logBeginTransaction(txnId);
+
+  const doc1 = { _id: new ObjectId(), name: 'TxnDoc1' };
+  await wal.logInsert('testdb', 'txncoll', doc1 as any, txnId);
+
+  const doc2 = { _id: new ObjectId(), name: 'TxnDoc2' };
+  await wal.logInsert('testdb', 'txncoll', doc2 as any, txnId);
+
+  await wal.logCommitTransaction(txnId);
+
+  const entries = wal.getTransactionEntries(txnId);
+
+  expect(entries.length).toEqual(4); // begin + 2 inserts + commit
+  expect(entries.every(e => e.txnId === txnId)).toBeTrue();
+});
+
+tap.test('wal: getTransactionEntries should return empty for unknown transaction', async () => {
+  const entries = wal.getTransactionEntries('unknown-txn-id');
+  expect(entries.length).toEqual(0);
+});
+
+// ============================================================================
+// getEntriesAfter Tests
+// ============================================================================
+
+tap.test('wal: getEntriesAfter should filter by LSN', async () => {
+  const currentLsn = wal.getCurrentLsn();
+
+  // Add more entries
+  const doc = { _id: new ObjectId(), name: 'AfterTest' };
+  await wal.logInsert('testdb', 'aftercoll', doc as any);
+
+  const entries = wal.getEntriesAfter(currentLsn);
+  expect(entries.length).toEqual(1);
+  expect(entries[0].lsn).toBeGreaterThan(currentLsn);
+});
+
+tap.test('wal: getEntriesAfter with LSN 0 should return all entries', async () => {
+  const entries = wal.getEntriesAfter(0);
+  expect(entries.length).toBeGreaterThan(0);
+  expect(entries.length).toEqual(wal.getCurrentLsn());
+});
+
+// ============================================================================
+// Checkpoint Tests
+// ============================================================================
+
+tap.test('wal: checkpoint should create checkpoint entry', async () => {
+  const lsn = await wal.checkpoint();
+
+  expect(lsn).toBeGreaterThan(0);
+
+  // After checkpoint, getEntriesAfter(checkpoint) should be limited
+  const entries = wal.getEntriesAfter(0);
+  expect(entries.some(e => e.operation === 'checkpoint')).toBeTrue();
+});
+
+// ============================================================================
+// Document Recovery Tests
+// ============================================================================
+
+tap.test('wal: recoverDocument should deserialize document from entry', async () => {
+  const originalDoc = { _id: new ObjectId(), name: 'RecoverTest', nested: { a: 1, b: 2 } };
+  const lsn = await wal.logInsert('testdb', 'recovercoll', originalDoc as any);
+
+  const entries = wal.getEntriesAfter(lsn - 1);
+  const entry = entries.find(e => e.lsn === lsn);
+
+  const recovered = wal.recoverDocument(entry!);
+
+  expect(recovered).toBeTruthy();
+  expect(recovered!.name).toEqual('RecoverTest');
+  expect(recovered!.nested.a).toEqual(1);
+  expect(recovered!.nested.b).toEqual(2);
+});
+
+tap.test('wal: recoverDocument should return null for entry without data', async () => {
+  const lsn = await wal.logBeginTransaction('recover-no-data');
+
+  const entries = wal.getEntriesAfter(lsn - 1);
+  const entry = entries.find(e => e.lsn === lsn);
+
+  const recovered = wal.recoverDocument(entry!);
+  expect(recovered).toBeNull();
+});
+
+tap.test('wal: recoverPreviousDocument should deserialize previous state', async () => {
+  const oldDoc = { _id: new ObjectId(), name: 'Old', value: 100 };
+  const newDoc = { ...oldDoc, name: 'New', value: 200 };
+
+  const lsn = await wal.logUpdate('testdb', 'recovercoll', oldDoc as any, newDoc as any);
+
+  const entries = wal.getEntriesAfter(lsn - 1);
+  const entry = entries.find(e => e.lsn === lsn);
+
+  const previous = wal.recoverPreviousDocument(entry!);
+
+  expect(previous).toBeTruthy();
+  expect(previous!.name).toEqual('Old');
+  expect(previous!.value).toEqual(100);
+});
+
+tap.test('wal: recoverPreviousDocument should return null for insert entry', async () => {
+  const doc = { _id: new ObjectId(), name: 'NoPrevious' };
+  const lsn = await wal.logInsert('testdb', 'recovercoll', doc as any);
+
+  const entries = wal.getEntriesAfter(lsn - 1);
+  const entry = entries.find(e => e.lsn === lsn);
+
+  const previous = wal.recoverPreviousDocument(entry!);
+  expect(previous).toBeNull();
+});
+
+// ============================================================================
+// WAL Persistence and Recovery Tests
+// ============================================================================
+
+tap.test('wal: should persist and recover entries', async () => {
+  // Close current WAL
+  await wal.close();
+
+  // Create new WAL instance and initialize (should recover)
+  const wal2 = new WAL(TEST_WAL_PATH, { checkpointInterval: 100 });
+  const result = await wal2.initialize();
+
+  // Should have recovered entries
+  expect(result.recoveredEntries).toBeArray();
+  // After checkpoint, there might not be many recoverable entries
+  // but getCurrentLsn should be preserved or reset
+
+  await wal2.close();
+});
+
+// ============================================================================
+// Entry Checksum Tests
+// ============================================================================
+
+tap.test('wal: entries should have valid checksums', async () => {
+  wal = new WAL(TEST_WAL_PATH + '.checksum', { checkpointInterval: 100 });
+  await wal.initialize();
+
+  const doc = { _id: new ObjectId(), name: 'ChecksumTest' };
+  const lsn = await wal.logInsert('testdb', 'checksumcoll', doc as any);
+
+  const entries = wal.getEntriesAfter(lsn - 1);
+  const entry = entries.find(e => e.lsn === lsn);
+
+  expect(entry!.checksum).toBeGreaterThan(0);
+  expect(typeof entry!.checksum).toEqual('number');
+});
+
+// ============================================================================
+// Edge Cases
+// ============================================================================
+
+tap.test('wal: should handle special characters in document', async () => {
+  const doc = {
+    _id: new ObjectId(),
+    name: 'Test\nWith\tSpecial\r\nChars',
+    emoji: '🎉',
+    unicode: '日本語',
+  };
+
+  const lsn = await wal.logInsert('testdb', 'specialcoll', doc as any);
+
+  const entries = wal.getEntriesAfter(lsn - 1);
+  const entry = entries.find(e => e.lsn === lsn);
+
+  const recovered = wal.recoverDocument(entry!);
+  expect(recovered!.name).toEqual('Test\nWith\tSpecial\r\nChars');
+  expect(recovered!.emoji).toEqual('🎉');
+  expect(recovered!.unicode).toEqual('日本語');
+});
+
+tap.test('wal: should handle binary data in documents', async () => {
+  const doc = {
+    _id: new ObjectId(),
+    binaryField: Buffer.from([0x00, 0xFF, 0x7F, 0x80]),
+  };
+
+  const lsn = await wal.logInsert('testdb', 'binarycoll', doc as any);
+
+  const entries = wal.getEntriesAfter(lsn - 1);
+  const entry = entries.find(e => e.lsn === lsn);
+
+  const recovered = wal.recoverDocument(entry!);
+  expect(recovered).toBeTruthy();
+});
+
+tap.test('wal: should handle nested documents', async () => {
+  const doc = {
+    _id: new ObjectId(),
+    level1: {
+      level2: {
+        level3: {
+          value: 'deep',
+        },
+      },
+    },
+  };
+
+  const lsn = await wal.logInsert('testdb', 'nestedcoll', doc as any);
+
+  const entries = wal.getEntriesAfter(lsn - 1);
+  const entry = entries.find(e => e.lsn === lsn);
+
+  const recovered = wal.recoverDocument(entry!);
+  expect(recovered!.level1.level2.level3.value).toEqual('deep');
+});
+
+tap.test('wal: should handle arrays in documents', async () => {
+  const doc = {
+    _id: new ObjectId(),
+    tags: ['a', 'b', 'c'],
+    numbers: [1, 2, 3],
+    mixed: [1, 'two', { three: 3 }],
+  };
+
+  const lsn = await wal.logInsert('testdb', 'arraycoll', doc as any);
+
+  const entries = wal.getEntriesAfter(lsn - 1);
+  const entry = entries.find(e => e.lsn === lsn);
+
+  const recovered = wal.recoverDocument(entry!);
+  expect(recovered!.tags).toEqual(['a', 'b', 'c']);
+  expect(recovered!.numbers).toEqual([1, 2, 3]);
+  expect(recovered!.mixed[2].three).toEqual(3);
+});
+
+// ============================================================================
+// Cleanup
+// ============================================================================
+
+tap.test('wal: cleanup', async () => {
+  await wal.close();
+  await cleanupTestFiles();
+  expect(true).toBeTrue();
+});
+
+export default tap.start();
diff --git a/ts/00_commitinfo_data.ts b/ts/00_commitinfo_data.ts
index 132ca22..6c26a42 100644
--- a/ts/00_commitinfo_data.ts
+++ b/ts/00_commitinfo_data.ts
@@ -3,6 +3,6 @@
  */
 export const commitinfo = {
   name: '@push.rocks/smartmongo',
-  version: '4.1.0',
+  version: '4.1.1',
   description: 'A module for creating and managing a local MongoDB instance for testing purposes.'
 }