Remove the overloads in epheraml transport

benchmarks/sekp256k1.ts

@@ -7,6 +7,7 @@ const alicePublicKey = await alice.getPublicKey();
 const bobPublicKey = await bob.getPublicKey();
 
 const keyStart = performance.now();
+
 const aliceSharedSecret = await alice.getSharedSecret(bobPublicKey);
 const bobSharedSecret = await bob.getSharedSecret(alicePublicKey);
 

benchmarks/storage.ts

@@ -1,5 +1,6 @@
 import { AESKey } from '../src/crypto/aes-key.js';
 import { StorageMemory, EncryptedStorage, type BaseStorage } from '../src/storage/index.js';
+import { BTreeCache, KvCache } from '../src/cache/index.js';
 
 // ---------------------------------------------------------------------------
 // Helpers
@@ -49,7 +50,13 @@ function fmtOps(ops: number): string {
 /**
  * Run a full suite of benchmarks against a given storage instance.
  */
-async function benchmarkStorage(label: string, storage: BaseStorage<Doc>, docs: Doc[]) {
+async function benchmarkStorage(
+  label: string,
+  storage: BaseStorage<Doc>,
+  docs: Doc[],
+  options: { supportsRangeOps?: boolean; hasAgeIndex?: boolean } = {},
+) {
+  const { supportsRangeOps = true, hasAgeIndex = false } = options;
   const count = docs.length;
   console.log(`\n${'='.repeat(60)}`);
   console.log(` ${label}  (${count.toLocaleString()} documents)`);
@@ -67,32 +74,63 @@ async function benchmarkStorage(label: string, storage: BaseStorage<Doc>, docs:
   });
   console.log(`  find()              ${findAllMs.toFixed(2)}ms  (${fmtOps((count / findAllMs) * 1000)} docs/sec)`);
 
-  // --- Find by indexed field (single-key lookup, repeated) ---
+  // --- Find by indexed field (equality) ---
   const lookupCount = Math.min(count, 1_000);
   const findIndexedMs = await time(async () => {
     for (let i = 0; i < lookupCount; i++) {
-      await storage.findOne({ id: `id-${i}` } as Partial<Doc>);
+      await storage.findOne({ id: `id-${i}` });
     }
   });
   console.log(`  findOne indexed      ${findIndexedMs.toFixed(2)}ms  (${fmtOps((lookupCount / findIndexedMs) * 1000)} ops/sec)  [${lookupCount} lookups]`);
 
-  // --- Find by non-indexed field (full scan, repeated) ---
+  // --- Find by non-indexed field (full scan) ---
   const scanCount = Math.min(count, 1_000);
   const findScanMs = await time(async () => {
     for (let i = 0; i < scanCount; i++) {
-      await storage.findOne({ email: `user-${i}@test.com` } as Partial<Doc>);
+      await storage.findOne({ email: `user-${i}@test.com` });
     }
   });
   console.log(`  findOne scan         ${findScanMs.toFixed(2)}ms  (${fmtOps((scanCount / findScanMs) * 1000)} ops/sec)  [${scanCount} lookups]`);
 
+  // --- Range queries ---
+  if (supportsRangeOps) {
+    // Wide range: 20% selectivity (10 out of 50 age values).
+    const rangeCount = Math.min(count, 100);
+    let rangeWideTotal = 0;
+    const findRangeWideMs = await time(async () => {
+      for (let i = 0; i < rangeCount; i++) {
+        const results = await storage.find({ age: { $gte: 30, $lt: 40 } });
+        rangeWideTotal += results.length;
+      }
+    });
+    const indexLabel = hasAgeIndex ? 'B+Tree' : 'scan';
+    console.log(`  find wide  [${indexLabel}]  ${findRangeWideMs.toFixed(2)}ms  (${fmtOps((rangeCount / findRangeWideMs) * 1000)} ops/sec)  [${rangeCount}x, ~${Math.round(rangeWideTotal / rangeCount)} hits, 20% sel.]`);
+
+    // Narrow range: 2% selectivity (1 out of 50 age values).
+    let rangeNarrowTotal = 0;
+    const findRangeNarrowMs = await time(async () => {
+      for (let i = 0; i < rangeCount; i++) {
+        const results = await storage.find({ age: { $gte: 42, $lt: 43 } });
+        rangeNarrowTotal += results.length;
+      }
+    });
+    console.log(`  find narrow [${indexLabel}]  ${findRangeNarrowMs.toFixed(2)}ms  (${fmtOps((rangeCount / findRangeNarrowMs) * 1000)} ops/sec)  [${rangeCount}x, ~${Math.round(rangeNarrowTotal / rangeCount)} hits, 2% sel.]`);
+
+    // --- Combined equality + operator ---
+    const comboCount = Math.min(count, 1_000);
+    const findComboMs = await time(async () => {
+      for (let i = 0; i < comboCount; i++) {
+        await storage.find({ id: `id-${i}`, age: { $gte: 20 } });
+      }
+    });
+    console.log(`  find idx+operator    ${findComboMs.toFixed(2)}ms  (${fmtOps((comboCount / findComboMs) * 1000)} ops/sec)  [${comboCount} queries]`);
+  }
+
   // --- Update by indexed field ---
   const updateCount = Math.min(count, 1_000);
   const updateMs = await time(async () => {
     for (let i = 0; i < updateCount; i++) {
-      await storage.updateOne(
-        { id: `id-${i}` } as Partial<Doc>,
-        { age: 99 } as Partial<Doc>,
-      );
+      await storage.updateOne({ id: `id-${i}` }, { name: `updated-${i}` });
     }
   });
   console.log(`  updateOne indexed    ${updateMs.toFixed(2)}ms  (${fmtOps((updateCount / updateMs) * 1000)} ops/sec)  [${updateCount} updates]`);
@@ -101,7 +139,7 @@ async function benchmarkStorage(label: string, storage: BaseStorage<Doc>, docs:
   const deleteCount = Math.min(count, 1_000);
   const deleteMs = await time(async () => {
     for (let i = 0; i < deleteCount; i++) {
-      await storage.deleteOne({ id: `id-${i}` } as Partial<Doc>);
+      await storage.deleteOne({ id: `id-${i}` });
     }
   });
   console.log(`  deleteOne indexed    ${deleteMs.toFixed(2)}ms  (${fmtOps((deleteCount / deleteMs) * 1000)} ops/sec)  [${deleteCount} deletes]`);
@@ -116,7 +154,7 @@ async function benchmarkStorage(label: string, storage: BaseStorage<Doc>, docs:
 // ---------------------------------------------------------------------------
 
 // ---------------------------------------------------------------------------
-// StorageMemory — indexed vs non-indexed
+// StorageMemory — B+ Tree range queries vs full scan
 // ---------------------------------------------------------------------------
 
 const DOC_COUNTS = [1_000, 10_000, 50_000];
@@ -124,32 +162,55 @@ const DOC_COUNTS = [1_000, 10_000, 50_000];
 for (const count of DOC_COUNTS) {
   const docs = generateDocs(count);
 
+  // Indexes on id, name, AND age with explicit B+ Tree cache.
+  const indexedWithAgeBTree = StorageMemory.from<Doc>(
+    ['id', 'name', 'age'],
+    new BTreeCache(),
+  );
+  await benchmarkStorage('StorageMemory (B+Tree cache, indexed: id,name,age)', indexedWithAgeBTree, docs, { hasAgeIndex: true });
+
+  // Same indexes, but KV cache (no range support).
+  const indexedWithAgeKv = StorageMemory.from<Doc>(
+    ['id', 'name', 'age'],
+    new KvCache(),
+  );
+  await benchmarkStorage('StorageMemory (KV cache, indexed: id,name,age)', indexedWithAgeKv, docs);
+
+  // Indexes on id, name only — range queries on age fall back to full scan.
   const indexed = StorageMemory.from<Doc>(['id', 'name']);
   await benchmarkStorage('StorageMemory (indexed: id,name)', indexed, docs);
 
+  // No indexes at all.
   const noIndex = StorageMemory.from<Doc>();
   await benchmarkStorage('StorageMemory (no indexes)', noIndex, docs);
 }
 
 // ---------------------------------------------------------------------------
-// EncryptedStorage — crypto overhead dominates, so use smaller counts
+// EncryptedStorage
 // ---------------------------------------------------------------------------
 
-const ENCRYPTED_DOC_COUNTS = [100, 1_000, 10_000];
+const ENCRYPTED_DOC_COUNTS = [100, 1_000];
 const encryptionKey = await AESKey.fromSeed('benchmark-key');
 
 for (const count of ENCRYPTED_DOC_COUNTS) {
   const docs = generateDocs(count);
 
-  // Encrypted + indexed backing store.
-  const encBase = StorageMemory.from<Record<string, string>>(['id', 'name']);
-  const encrypted = EncryptedStorage.from<Doc>(encBase, encryptionKey);
-  await benchmarkStorage('EncryptedStorage (indexed backing store)', encrypted, docs);
+  // Indexed + plaintextKeys (age) — range queries on age use B+ Tree via backing store.
+  const encBaseA = StorageMemory.from<Record<string, any>>(['id', 'name', 'age']);
+  const encA = EncryptedStorage.from<Doc>(encBaseA, encryptionKey, {
+    plaintextKeys: ['age'],
+  });
+  await benchmarkStorage('Encrypted (indexed+age, plaintextKeys: age)', encA, docs, { hasAgeIndex: true });
 
-  // Encrypted + no-index backing store.
-  const encBaseNoIdx = StorageMemory.from<Record<string, string>>();
-  const encryptedNoIdx = EncryptedStorage.from<Doc>(encBaseNoIdx, encryptionKey);
-  await benchmarkStorage('EncryptedStorage (no indexes)', encryptedNoIdx, docs);
+  // Indexed, fully encrypted — no range ops.
+  const encBaseB = StorageMemory.from<Record<string, any>>(['id', 'name']);
+  const encB = EncryptedStorage.from<Doc>(encBaseB, encryptionKey);
+  await benchmarkStorage('Encrypted (indexed, fully encrypted)', encB, docs, { supportsRangeOps: false });
+
+  // No indexes, fully encrypted — worst case.
+  const encBaseC = StorageMemory.from<Record<string, any>>();
+  const encC = EncryptedStorage.from<Doc>(encBaseC, encryptionKey);
+  await benchmarkStorage('Encrypted (no indexes, fully encrypted)', encC, docs, { supportsRangeOps: false });
 }
 
 console.log('\nDone.\n');

package.json

@@ -6,8 +6,13 @@
   "scripts": {
     "build": "tsc",
     "format": "prettier --write .",
-    "test": "echo \"Error: no test specified\" && exit 1",
     
+    "test": "vitest --run",
+    "test:watch": "vitest",
+
+    "benchmark:sha256": "tsx benchmarks/sha256.ts",
+    "benchmark:diffie-helman": "tsx benchmarks/diffie-helman.ts",
+    "benchmark:encryption": "tsx benchmarks/sekp256k1.ts",
     "benchmark:storage": "tsx benchmarks/storage.ts"
   },
   "keywords": [],

src/cache/b-tree-cache.ts

@@ -0,0 +1,79 @@
+import { BPlusTree, type BPlusTreeEntry } from 'src/utils/btree.js';
+
+import { BaseCache, type CacheRangeOptions } from './base-cache.js';
+
+function tupleCompare(a: any[], b: any[]): number {
+  const len = Math.min(a.length, b.length);
+  for (let i = 0; i < len; i++) {
+    if (a[i] < b[i]) return -1;
+    if (a[i] > b[i]) return 1;
+  }
+  return a.length - b.length;
+}
+
+/**
+ * B+ tree-backed cache implementation.
+ *
+ * - Equality: O(log n)
+ * - Range: O(log n + k)
+ */
+export class BTreeCache extends BaseCache {
+  private trees = new Map<string, BPlusTree<any, number>>();
+
+  registerIndex(indexName: string, fields: string[]): void {
+    if (this.trees.has(indexName)) return;
+    const comparator = fields.length > 1 ? tupleCompare : undefined;
+    this.trees.set(indexName, new BPlusTree<any, number>(32, comparator));
+  }
+
+  clearIndex(indexName: string): void {
+    const tree = this.trees.get(indexName);
+    if (!tree) return;
+    tree.clear();
+  }
+
+  insert(indexName: string, key: any, internalKey: number): void {
+    const tree = this.trees.get(indexName);
+    if (!tree) return;
+    tree.insert(key, internalKey);
+  }
+
+  delete(indexName: string, key: any, internalKey: number): void {
+    const tree = this.trees.get(indexName);
+    if (!tree) return;
+    tree.delete(key, internalKey);
+  }
+
+  get(indexName: string, key: any): Iterable<number> {
+    const tree = this.trees.get(indexName);
+    if (!tree) return [];
+    return tree.get(key) ?? [];
+  }
+
+  range(
+    indexName: string,
+    min?: any,
+    max?: any,
+    options: CacheRangeOptions = {},
+  ): Iterable<number> | null {
+    const tree = this.trees.get(indexName);
+    if (!tree) return [];
+    const entries = tree.range(min, max, options);
+    return this.flattenEntryKeys(entries);
+  }
+
+  createChild(): BaseCache {
+    return new BTreeCache();
+  }
+
+  private flattenEntryKeys(entries: BPlusTreeEntry<any, number>[]): number[] {
+    const result: number[] = [];
+    for (const entry of entries) {
+      for (const key of entry.values) {
+        result.push(key);
+      }
+    }
+    return result;
+  }
+}
+

src/cache/base-cache.ts

@@ -0,0 +1,37 @@
+export type CacheRangeOptions = {
+  lowerInclusive?: boolean;
+  upperInclusive?: boolean;
+};
+
+/**
+ * Shared cache abstraction used by storage adapters for secondary indexes.
+ *
+ * Implementations may support only equality (`get`) or both equality and
+ * range queries (`range`). Returning `null` from `range` indicates the cache
+ * cannot serve that range query efficiently.
+ */
+export abstract class BaseCache {
+  abstract registerIndex(indexName: string, fields: string[]): void;
+
+  abstract clearIndex(indexName: string): void;
+
+  abstract insert(indexName: string, key: any, internalKey: number): void;
+
+  abstract delete(indexName: string, key: any, internalKey: number): void;
+
+  abstract get(indexName: string, key: any): Iterable<number>;
+
+  abstract range(
+    indexName: string,
+    min?: any,
+    max?: any,
+    options?: CacheRangeOptions,
+  ): Iterable<number> | null;
+
+  /**
+   * Create a new empty cache instance of the same concrete type.
+   * Used by deriveChild() to preserve cache strategy across children.
+   */
+  abstract createChild(): BaseCache;
+}
+

src/cache/index.ts

@@ -0,0 +1,4 @@
+export * from './base-cache.js';
+export * from './b-tree-cache.js';
+export * from './kv-cache.js';
+

src/cache/kv-cache.ts

@@ -0,0 +1,69 @@
+import { BaseCache, type CacheRangeOptions } from './base-cache.js';
+
+/**
+ * Hash-map cache implementation.
+ *
+ * - Equality: O(1) average
+ * - Range: unsupported (returns null -> caller falls back to scan)
+ */
+export class KvCache extends BaseCache {
+  private indexes = new Map<string, Map<string, Set<number>>>();
+
+  registerIndex(indexName: string, _fields: string[]): void {
+    if (!this.indexes.has(indexName)) {
+      this.indexes.set(indexName, new Map());
+    }
+  }
+
+  clearIndex(indexName: string): void {
+    this.indexes.get(indexName)?.clear();
+  }
+
+  insert(indexName: string, key: any, internalKey: number): void {
+    const index = this.indexes.get(indexName);
+    if (!index) return;
+
+    const keyStr = this.encodeKey(key);
+    const set = index.get(keyStr) ?? new Set<number>();
+    set.add(internalKey);
+    index.set(keyStr, set);
+  }
+
+  delete(indexName: string, key: any, internalKey: number): void {
+    const index = this.indexes.get(indexName);
+    if (!index) return;
+
+    const keyStr = this.encodeKey(key);
+    const set = index.get(keyStr);
+    if (!set) return;
+
+    set.delete(internalKey);
+    if (set.size === 0) {
+      index.delete(keyStr);
+    }
+  }
+
+  get(indexName: string, key: any): Iterable<number> {
+    const index = this.indexes.get(indexName);
+    if (!index) return [];
+    return index.get(this.encodeKey(key)) ?? [];
+  }
+
+  range(
+    _indexName: string,
+    _min?: any,
+    _max?: any,
+    _options?: CacheRangeOptions,
+  ): Iterable<number> | null {
+    return null;
+  }
+
+  createChild(): BaseCache {
+    return new KvCache();
+  }
+
+  private encodeKey(value: any): string {
+    return JSON.stringify(value);
+  }
+}
+

src/protocols/whisper.ts

@@ -19,6 +19,24 @@
  *  Only allow specific parameters, unless prefixed with 'x-'
  */
 
+/**
+ * What I *think* this is:
+ * Deps: List of transports
+ * 
+ * Recieving: 
+ * 1. Create from a list of tranpsports and a lsit of items. 
+ * 2. Starts listening on all of the transports and returns a URL (maybe a promise too? Not sure whether it should be a promise or event emitter. Maybe both?)
+ * 3. Once it recieves a message, decrypt it and resolve the promise with the message.
+ * 
+ * Sending:
+ * 1. Create from a list of transports and the URL.
+ * 2. Encrypt the message
+ * 3. Send the encrypted message to all of the transports that are in both the requestURL and the list of transports.
+ * 
+ * Possibilities:
+ * - Non-ephemeral. Keep listeners alive to allow for multiple requests
+ */
+
 import { z } from 'zod/v4';
 
 import { PublicKey } from 'src/crypto/index.js';

src/storage/base-storage.ts

@@ -19,6 +19,86 @@ export type FindOptions = {
  */
 export type IndexDefinition = string[] | string[][];
 
+/**
+ * MongoDB-style comparison and string operators for a single field value.
+ *
+ * - Comparison operators ($eq, $ne, $lt, $lte, $gt, $gte) are available for
+ *   all value types.
+ * - String operators ($startsWith, $contains) are only available when the
+ *   field value type extends `string`.
+ * - Field-level $not wraps another operator set, inverting its result:
+ *   `{ age: { $not: { $gte: 18 } } }` matches documents where age < 18.
+ */
+export type ComparisonOperators<V> = {
+  $eq?: V;
+  $ne?: V;
+  $lt?: V;
+  $lte?: V;
+  $gt?: V;
+  $gte?: V;
+  $not?: ComparisonOperators<V>;
+} & ([V] extends [string] ? { $startsWith?: string; $contains?: string } : {});
+
+/**
+ * A filter value for a single field — either a plain value (equality shorthand)
+ * or an object of comparison operators.
+ */
+export type FieldFilter<V> = V | ComparisonOperators<V>;
+
+/**
+ * Keys that represent top-level logical operators in a filter,
+ * as opposed to document field names.
+ */
+const LOGICAL_KEYS = new Set(['$and', '$or', '$not']);
+
+/**
+ * Returns true when `key` is a top-level logical operator ($and, $or, $not)
+ * rather than a document field name.
+ */
+export function isLogicalKey(key: string): boolean {
+  return LOGICAL_KEYS.has(key);
+}
+
+/**
+ * Query filter that supports equality shorthand, comparison operators,
+ * and top-level logical operators ($and, $or, $not).
+ *
+ * @example
+ * // Equality shorthand
+ * { name: 'foo' }
+ *
+ * // Comparison operators
+ * { age: { $gte: 18, $lt: 65 } }
+ *
+ * // String operators (type-safe — only on string fields)
+ * { name: { $startsWith: 'A' } }
+ *
+ * // Logical operators
+ * { $or: [{ name: 'foo' }, { age: { $gte: 18 } }] }
+ * { $not: { name: 'bar' } }
+ * { $and: [{ age: { $gte: 18 } }, { name: { $startsWith: 'A' } }] }
+ */
+export type Filter<T extends Record<string, any>> = {
+  [K in keyof T]?: FieldFilter<T[K]>;
+} & {
+  $and?: Filter<T>[];
+  $or?: Filter<T>[];
+  $not?: Filter<T>;
+};
+
+/**
+ * Detect whether a filter value is an operator object (e.g. `{ $lt: 50 }`)
+ * rather than a plain value. Guards against Date and Array which are objects
+ * but represent document values, not operators.
+ */
+export function isOperatorObject(value: unknown): value is ComparisonOperators<any> {
+  return value !== null
+    && typeof value === 'object'
+    && !Array.isArray(value)
+    && !(value instanceof Date)
+    && Object.keys(value).some((k) => k.startsWith('$'));
+}
+
 export type StorageEvent<T = Record<string, any>> = {
   insert: {
     value: T;
@@ -54,7 +134,7 @@ export abstract class BaseStorage<
    * Find a single document that matches the filter
    * @param filter MongoDB-like query filter
    */
-  async findOne(filter?: Partial<T>): Promise<T | null> {
+  async findOne(filter?: Filter<T>): Promise<T | null> {
     const results = await this.find(filter);
     return results.length > 0 ? results[0] : null;
   }
@@ -64,7 +144,7 @@ export abstract class BaseStorage<
    * @param filter MongoDB-like query filter
    * @param options Query options (limit, skip, sort)
    */
-  abstract find(filter?: Partial<T>, options?: FindOptions): Promise<T[]>;
+  abstract find(filter?: Filter<T>, options?: FindOptions): Promise<T[]>;
 
   /**
    * Update a document that matches the filter
@@ -72,7 +152,7 @@ export abstract class BaseStorage<
    * @param update Document or fields to update
    * @returns True if a document was updated, false otherwise
    */
-  async updateOne(filter: Partial<T>, update?: Partial<T>): Promise<boolean> {
+  async updateOne(filter: Filter<T>, update?: Partial<T>): Promise<boolean> {
     const results = await this.updateMany(filter, update, { limit: 1 });
     return results > 0;
   }
@@ -85,7 +165,7 @@ export abstract class BaseStorage<
    * @returns Number of documents updated
    */
   abstract updateMany(
-    filter: Partial<T>,
+    filter: Filter<T>,
     update: Partial<T>,
     options?: Partial<FindOptions>,
   ): Promise<number>;
@@ -95,7 +175,7 @@ export abstract class BaseStorage<
    * @param filter Query to match the document to delete
    * @returns True if a document was deleted, false otherwise
    */
-  async deleteOne(filter: Partial<T>): Promise<boolean> {
+  async deleteOne(filter: Filter<T>): Promise<boolean> {
     const results = await this.deleteMany(filter, { limit: 1 });
     return results > 0;
   }
@@ -107,8 +187,8 @@ export abstract class BaseStorage<
    * @returns Number of documents deleted
    */
   abstract deleteMany(
-    filter: Partial<T>,
-    options: Partial<FindOptions>,
+    filter: Filter<T>,
+    options?: Partial<FindOptions>,
   ): Promise<number>;
 
   /**

src/storage/encrypted-storage.ts

@@ -3,15 +3,36 @@ import { Packr } from 'msgpackr';
 import { AESKey } from 'src/crypto/aes-key.js';
 import { Bytes } from 'src/crypto/bytes.js';
 
-import { BaseStorage, type FindOptions } from './base-storage.js';
+import {
+  BaseStorage,
+  type ComparisonOperators,
+  type FindOptions,
+  type Filter,
+  isOperatorObject,
+  isLogicalKey,
+} from './base-storage.js';
 
-import { encodeExtendedJson, decodeExtendedJson, encodeExtendedJsonObject, decodeExtendedJsonObject } from 'src/utils/ext-json.js';
+import { encodeExtendedJsonObject, decodeExtendedJsonObject } from 'src/utils/ext-json.js';
+
+export type EncryptedStorageOptions = {
+  /**
+   * Fields that should be stored in plaintext (not encrypted).
+   * These fields retain their original types in the backing store, which
+   * allows comparison operators ($lt, $gt, etc.) to work on them.
+   * All other fields are encrypted.
+   */
+  plaintextKeys?: string[];
+};
 
 export class EncryptedStorage<
   T extends Record<string, any> = Record<string, any>,
 > extends BaseStorage<T> {
-  static from<T>(storage: BaseStorage<Record<string, string>>, key: AESKey) {
-    return new EncryptedStorage<T>(storage, key);
+  static from<T>(
+    storage: BaseStorage<Record<string, any>>,
+    key: AESKey,
+    options?: EncryptedStorageOptions,
+  ) {
+    return new EncryptedStorage<T>(storage, key, options);
   }
 
   private readonly msgpackr = new Packr({
@@ -33,34 +54,32 @@ export class EncryptedStorage<
    */
   private readonly decryptCache = new Map<string, any>();
 
+  /** Set of field names that are stored in plaintext (not encrypted). */
+  private readonly plaintextKeys: Set<string>;
+
   constructor(
-    private readonly storage: BaseStorage<Record<string, string>>,
+    private readonly storage: BaseStorage<Record<string, any>>,
     private readonly key: AESKey,
+    options?: EncryptedStorageOptions,
   ) {
     super();
 
-    // Forward events from the underlying storage, decrypting the data
-    this.storage.on('insert', async (event) => {
-      // De-crypt the value before emitting the event.
-      const decryptedValue = await this.convertToDecrypted(event.value as Record<string, string>);
+    this.plaintextKeys = new Set(options?.plaintextKeys ?? []);
     
-      // Re-emit the insert event with the original payload.
+    // Forward events from the underlying storage, converting data back.
+    this.storage.on('insert', async (event) => {
+      const decryptedValue = await this.convertFromStorage(event.value);
       this.emit('insert', { value: decryptedValue });
     });
     
     this.storage.on('update', async (event) => {
-      // Decrypt both old and new values before re-emitting.
-      const decryptedOldValue = await this.convertToDecrypted(event.oldValue as Record<string, string>);
-      const decryptedValue = await this.convertToDecrypted(event.value as Record<string, string>);
-
+      const decryptedOldValue = await this.convertFromStorage(event.oldValue);
+      const decryptedValue = await this.convertFromStorage(event.value);
       this.emit('update', { oldValue: decryptedOldValue, value: decryptedValue });
     });
     
     this.storage.on('delete', async (event) => {
-      // De-crypt the value before emitting the event.
-      const decryptedValue = await this.convertToDecrypted(event.value as Record<string, string>);
-
-      // Re-emit the delete event with the original payload.
+      const decryptedValue = await this.convertFromStorage(event.value);
       this.emit('delete', { value: decryptedValue });
     });
     
@@ -70,53 +89,83 @@ export class EncryptedStorage<
   }
 
   async insertMany(documents: Array<T>): Promise<void> {
-    // Encrypt all documents in parallel.
-    const encrypted = await Promise.all(
-      documents.map((doc) => this.convertToEncrypted(doc)),
+    const converted = await Promise.all(
+      documents.map((doc) => this.convertForStorage(doc)),
     );
-    await this.storage.insertMany(encrypted);
+    await this.storage.insertMany(converted);
   }
 
-  async find(filter?: Partial<T>, options?: FindOptions): Promise<T[]> {
-    const encryptedFilter = filter ? await this.convertToEncrypted(filter) : undefined;
-    const documents = await this.storage.find(encryptedFilter, options);
+  async find(filter?: Filter<T>, options?: FindOptions): Promise<T[]> {
+    const convertedFilter = filter
+      ? await this.convertFilterForStorage(filter)
+      : undefined;
+    const documents = await this.storage.find(convertedFilter, options);
     return Promise.all(
-      documents.map(async (document) => this.convertToDecrypted(document)),
+      documents.map((doc) => this.convertFromStorage(doc)),
     );
   }
 
   async updateMany(
-    filter: Partial<T>,
+    filter: Filter<T>,
     update: Partial<T>,
     options: Partial<FindOptions> = {},
   ): Promise<number> {
-    const encryptedFilter = await this.convertToEncrypted(filter);
-    const encryptedUpdate = await this.convertToEncrypted(update);
-    return this.storage.updateMany(encryptedFilter, encryptedUpdate, options);
+    const convertedFilter = await this.convertFilterForStorage(filter);
+    const convertedUpdate = await this.convertForStorage(update);
+    return this.storage.updateMany(convertedFilter, convertedUpdate, options);
   }
 
   async deleteMany(
-    filter: Partial<T>,
+    filter: Filter<T>,
     options: Partial<FindOptions> = {},
   ): Promise<number> {
-    const encryptedFilter = await this.convertToEncrypted(filter);
-    return this.storage.deleteMany(encryptedFilter, options);
+    const convertedFilter = await this.convertFilterForStorage(filter);
+    return this.storage.deleteMany(convertedFilter, options);
   }
 
   deriveChild<C>(path: string): BaseStorage<C> {
-    return EncryptedStorage.from(this.storage.deriveChild(path), this.key);
+    return EncryptedStorage.from<C>(
+      this.storage.deriveChild(path),
+      this.key,
+      { plaintextKeys: [...this.plaintextKeys] },
+    );
   }
 
-  private async convertToEncrypted(
+  // ---------------------------------------------------------------------------
+  // Storage conversion — documents (insert/update values)
+  // ---------------------------------------------------------------------------
+
+  /**
+   * Convert a document for storage. Encrypted fields are encrypted;
+   * plaintext fields are passed through with value formatting only.
+   */
+  private async convertForStorage(
     document: Partial<T>,
-  ): Promise<Record<string, string>> {
-    const encrypted: Record<string, string> = {};
+  ): Promise<Record<string, any>> {
+    const result: Record<string, any> = {};
     const formattedDocument = this.formatDocumentForEncryption(document);
     const entries = Object.entries(formattedDocument);
 
-    // Encrypt all fields in parallel, using the cache when possible.
-    const results = await Promise.all(
-      entries.map(async ([key, value]) => {
+    // Split into plaintext and encrypted fields.
+    const plaintextEntries: Array<[string, any]> = [];
+    const encryptedEntries: Array<[string, any]> = [];
+
+    for (const entry of entries) {
+      if (this.plaintextKeys.has(entry[0])) {
+        plaintextEntries.push(entry);
+      } else {
+        encryptedEntries.push(entry);
+      }
+    }
+
+    // Plaintext fields pass through directly.
+    for (const [key, value] of plaintextEntries) {
+      result[key] = value;
+    }
+
+    // Encrypt fields in parallel, with memoization.
+    const encrypted = await Promise.all(
+      encryptedEntries.map(async ([key, value]) => {
         const bin = this.msgpackr.pack(value);
         const cacheKey = Bytes.from(bin).toBase64();
 
@@ -131,21 +180,36 @@ export class EncryptedStorage<
       }),
     );
 
-    for (const [key, ciphertext] of results) {
-      encrypted[key] = ciphertext;
+    for (const [key, ciphertext] of encrypted) {
+      result[key] = ciphertext;
     }
 
-    return encrypted;
+    return result;
   }
 
-  private async convertToDecrypted(
-    document: Record<string, string>,
+  /**
+   * Convert a stored document back to its original form. Encrypted fields
+   * are decrypted; plaintext fields are passed through with value formatting.
+   */
+  private async convertFromStorage(
+    document: Record<string, any>,
   ): Promise<T> {
     const entries = Object.entries(document);
 
-    // Decrypt all fields in parallel, using the cache when possible.
-    const results = await Promise.all(
-      entries.map(async ([key, ciphertext]) => {
+    const plaintextEntries: Array<[string, any]> = [];
+    const encryptedEntries: Array<[string, any]> = [];
+
+    for (const entry of entries) {
+      if (this.plaintextKeys.has(entry[0])) {
+        plaintextEntries.push(entry);
+      } else {
+        encryptedEntries.push(entry);
+      }
+    }
+
+    // Decrypt encrypted fields in parallel, with memoization.
+    const decrypted = await Promise.all(
+      encryptedEntries.map(async ([key, ciphertext]) => {
         let value = this.decryptCache.get(ciphertext);
         if (value === undefined) {
           const bin = await this.key.decrypt(Bytes.fromBase64(ciphertext));
@@ -156,70 +220,159 @@ export class EncryptedStorage<
       }),
     );
 
-    const decrypted: Record<string, any> = {};
-    for (const [key, value] of results) {
-      decrypted[key] = value;
+    const result: Record<string, any> = {};
+
+    for (const [key, value] of plaintextEntries) {
+      result[key] = value;
+    }
+    for (const [key, value] of decrypted) {
+      result[key] = value;
     }
 
-    const decodedDocument = this.formatDocumentFromDecryption(decrypted);
+    const decodedDocument = this.formatDocumentFromDecryption(result);
     return decodedDocument as T;
   }
 
-  private formatDocumentForEncryption(document: any): any {
-    // First, iterate through each key and value in the document and format the value for encryption.
-    const formattedDocument: any = {};
+  // ---------------------------------------------------------------------------
+  // Storage conversion — filters (may contain operator objects)
+  // ---------------------------------------------------------------------------
 
+  /**
+   * Convert a query filter for storage. Handles plain equality values,
+   * operator objects, and top-level logical operators ($and, $or, $not).
+   *
+   * - Plaintext fields: values and operator objects pass through as-is.
+   * - Encrypted fields: plain values are encrypted. Operator objects throw
+   *   because range/string comparisons are meaningless on ciphertext.
+   * - Logical operators: sub-filters are recursively converted.
+   */
+  private async convertFilterForStorage(
+    filter: Filter<T>,
+  ): Promise<Filter<Record<string, any>>> {
+    const result: Record<string, any> = {};
+    const entries = Object.entries(filter);
+
+    // Recursively convert logical operator sub-filters.
+    if (filter.$and) {
+      result.$and = await Promise.all(
+        filter.$and.map((f) => this.convertFilterForStorage(f)),
+      );
+    }
+    if (filter.$or) {
+      result.$or = await Promise.all(
+        filter.$or.map((f) => this.convertFilterForStorage(f)),
+      );
+    }
+    if (filter.$not) {
+      result.$not = await this.convertFilterForStorage(filter.$not);
+    }
+
+    const encryptionTasks: Array<Promise<readonly [string, any]>> = [];
+
+    for (const [key, value] of entries) {
+      // Logical operator keys are already handled above.
+      if (isLogicalKey(key)) continue;
+
+      if (this.plaintextKeys.has(key)) {
+        // Plaintext field — pass through (including operator objects).
+        result[key] = isOperatorObject(value)
+          ? this.formatOperatorValuesForStorage(value)
+          : this.formatValueForEncryption(value);
+      } else if (isOperatorObject(value)) {
+        // Encrypted field with an operator — not supported.
+        throw new Error(
+          `Operators ($lt, $gt, $startsWith, $contains, $not, etc.) cannot be used on encrypted field '${key}'. ` +
+          `Add '${key}' to plaintextKeys if you need operator queries on this field.`,
+        );
+      } else {
+        // Encrypted field with a plain equality value — encrypt it.
+        const formatted = this.formatValueForEncryption(value);
+        encryptionTasks.push(
+          (async () => {
+            const bin = this.msgpackr.pack(formatted);
+            const cacheKey = Bytes.from(bin).toBase64();
+
+            let ciphertext = this.encryptCache.get(cacheKey);
+            if (ciphertext === undefined) {
+              const encryptedValue = await this.key.encrypt(bin, true);
+              ciphertext = encryptedValue.toBase64();
+              this.encryptCache.set(cacheKey, ciphertext);
+            }
+
+            return [key, ciphertext] as const;
+          })(),
+        );
+      }
+    }
+
+    const encryptedResults = await Promise.all(encryptionTasks);
+    for (const [key, ciphertext] of encryptedResults) {
+      result[key] = ciphertext;
+    }
+
+    return result;
+  }
+
+  /**
+   * Normalize operator object values for plaintext fields so they use the
+   * same storage representation as document values (e.g. Date).
+   */
+  private formatOperatorValuesForStorage(
+    ops: ComparisonOperators<any>,
+  ): ComparisonOperators<any> {
+    const result: Record<string, any> = {};
+    for (const [op, value] of Object.entries(ops)) {
+      if (op === '$not' && isOperatorObject(value)) {
+        result[op] = this.formatOperatorValuesForStorage(value);
+        continue;
+      }
+      result[op] = this.formatValueForEncryption(value);
+    }
+    return result as ComparisonOperators<any>;
+  }
+
+  // ---------------------------------------------------------------------------
+  // Value formatting
+  // ---------------------------------------------------------------------------
+
+  private formatDocumentForEncryption(document: any): any {
+    const formattedDocument: any = {};
     for (const [key, value] of Object.entries(document)) {
       formattedDocument[key] = this.formatValueForEncryption(value);
     }
-
-    // Then, encode the document to extended JSON.
-    const encodedDocument = encodeExtendedJsonObject(formattedDocument);
-
-    return encodedDocument;
+    return encodeExtendedJsonObject(formattedDocument);
   }
 
   private formatDocumentFromDecryption(document: any): any {
-    // First, decode the document from extended JSON.
     const decodedDocument = decodeExtendedJsonObject(document);
-
-    // Then, iterate through each key and value in the document and format the value from decryption.
     for (const [key, value] of Object.entries(decodedDocument)) {
       decodedDocument[key] = this.formatValueFromDecryption(value);
     }
-
     return decodedDocument;
   }
 
+  /**
+   * Format a value before encryption. Converts types that msgpackr
+   * doesn't natively support (e.g. Date) into serialisable forms.
+   */
   private formatValueForEncryption(value: any): any {
-    // msgpackr doesnt support Date, so we need to convert it to a string.
     if (value instanceof Date) {
       return `<Date: ${value.getTime()}>`;
     }
-
     return value;
   }
 
+  /**
+   * Restore a value after decryption. Reverses the transformations
+   * applied by `formatValueForEncryption`.
+   */
   private formatValueFromDecryption(value: any): any {
-    // msgpackr doesnt support Date, so we need to convert it to a Date.
     if (typeof value === 'string') {
-      // Check if this value matches an Extended JSON encoded date.
-      // TODO: Do this without a regex for performance reasons.
-      // const dateMatch = value.match(/<Date: (?<time>[0-9]+)>/);
-
-      // Without regex
       if (value.startsWith('<Date: ') && value.endsWith('>')) {
         const time = value.slice(7, -1);
         return new Date(parseInt(time));
       }
-
-      // If it does, convert it to a Date.
-      // if (dateMatch) {
-      //   const { time } = dateMatch.groups!;
-      //   return new Date(parseInt(time));
-      // }
     }
-
     return value;
   }
 }

src/storage/storage-localstorage.ts

@@ -1,4 +1,13 @@
-import { BaseStorage, FindOptions, type IndexDefinition } from './base-storage.js';
+import {
+  BaseStorage,
+  FindOptions,
+  type IndexDefinition,
+  type Filter,
+  type ComparisonOperators,
+  isOperatorObject,
+  isLogicalKey,
+} from './base-storage.js';
+import { BaseCache, BTreeCache } from 'src/cache/index.js';
 
 /**
  * Key prefix separator used to namespace documents within localStorage.
@@ -18,7 +27,14 @@ const MANIFEST_SUFFIX = '__keys__';
 const COUNTER_SUFFIX = '__next__';
 
 /**
- * Separator used when joining multiple field values into a single index key.
+ * Suffix for the mutation/version marker. This value increments on every
+ * write operation so other tabs can detect index-staleness even when the
+ * manifest key set itself is unchanged (e.g. updateMany).
+ */
+const VERSION_SUFFIX = '__version__';
+
+/**
+ * Separator used when joining field names to create the index map key.
  */
 const INDEX_KEY_SEP = '\x00';
 
@@ -43,9 +59,9 @@ function normalizeIndexes(indexes?: IndexDefinition): string[][] {
  * tracks all internal keys so that read operations avoid scanning every
  * key in localStorage.
  *
- * Optional indexes provide fast lookups when a query filter matches
- * an index exactly. Indexes are held in memory and rebuilt only when a
- * cross-tab manifest change is detected.
+ * Optional indexes are backed by B+ Trees, providing O(log n) equality
+ * lookups and O(log n + k) range queries. Indexes are held in memory and
+ * rebuilt only when a cross-tab manifest change is detected.
  *
  * Because localStorage is synchronous and string-only, all values are
  * JSON-serialised on write and parsed on read.
@@ -59,8 +75,9 @@ export class StorageLocalStorage<
   static from<T extends Record<string, any>>(
     prefix = 'qs',
     indexes?: IndexDefinition,
+    cache?: BaseCache,
   ): StorageLocalStorage<T> {
-    return new StorageLocalStorage<T>(prefix, indexes);
+    return new StorageLocalStorage<T>(prefix, indexes, cache);
   }
 
   /**
@@ -79,17 +96,13 @@ export class StorageLocalStorage<
    * valid and we skip the expensive rebuild.
    */
   private lastManifestRaw: string;
+  private lastVersionRaw: string;
 
   /** The normalized index definitions supplied at construction time. */
   private indexDefs: string[][];
 
-  /**
-   * Secondary index maps (same structure as StorageMemory).
-   * Outer key  = index name (joined field names).
-   * Inner key  = index value (joined field values from a document).
-   * Inner value = set of internal numeric keys.
-   */
-  private indexes: Map<string, Map<string, Set<number>>>;
+  /** Secondary index cache (B-Tree or KV implementation). */
+  private cache: BaseCache;
 
   /** Lazily-created child storage instances. */
   private children: Map<string, StorageLocalStorage<any>>;
@@ -97,18 +110,21 @@ export class StorageLocalStorage<
   constructor(
     private readonly prefix: string = 'qs',
     indexes?: IndexDefinition,
+    cache?: BaseCache,
   ) {
     super();
 
     this.children = new Map();
     this.indexDefs = normalizeIndexes(indexes);
-    this.indexes = new Map();
+    this.cache = cache ?? new BTreeCache();
     for (const fields of this.indexDefs) {
-      this.indexes.set(fields.join(INDEX_KEY_SEP), new Map());
+      const name = fields.join(INDEX_KEY_SEP);
+      this.cache.registerIndex(name, fields);
     }
 
     // Bootstrap from localStorage.
     this.lastManifestRaw = '';
+    this.lastVersionRaw = '';
     this.manifest = new Set();
     this.nextKey = 0;
     this.refreshManifest();
@@ -132,23 +148,24 @@ export class StorageLocalStorage<
     this.persistManifest();
   }
 
-  async find(filter?: Partial<T>, options?: FindOptions): Promise<T[]> {
+  async find(filter?: Filter<T>, options?: FindOptions): Promise<T[]> {
     this.refreshManifest();
 
     let results: T[];
-    const indexedKeys = this.resolveIndexKeys(filter);
+    const resolution = this.resolveIndexKeys(filter);
+
+    if (resolution !== null) {
+      const { keys, resolvedFields } = resolution;
+      const needsVerification = this.filterNeedsVerification(filter, resolvedFields);
 
-    if (indexedKeys !== null) {
-      // Use the index to narrow which documents we read from localStorage.
       results = [];
-      for (const key of indexedKeys) {
+      for (const key of keys) {
         const raw = localStorage.getItem(this.docKey(key));
         if (raw === null) continue;
         const doc = JSON.parse(raw) as T;
-        if (this.matchesFilter(doc, filter)) {
+        if (needsVerification && !this.matchesFilter(doc, filter)) continue;
         results.push(doc);
       }
-      }
     } else {
       // Full scan over all documents in the manifest.
       results = [];
@@ -175,7 +192,7 @@ export class StorageLocalStorage<
   }
 
   async updateMany(
-    filter: Partial<T>,
+    filter: Filter<T>,
     update: Partial<T>,
     options: Partial<FindOptions> = {},
   ): Promise<number> {
@@ -207,7 +224,7 @@ export class StorageLocalStorage<
   }
 
   async deleteMany(
-    filter: Partial<T>,
+    filter: Filter<T>,
     options: Partial<FindOptions> = {},
   ): Promise<number> {
     this.refreshManifest();
@@ -239,7 +256,7 @@ export class StorageLocalStorage<
       const childPrefix = `${this.prefix}${KEY_SEP}${path}`;
       this.children.set(
         path,
-        new StorageLocalStorage<C>(childPrefix, this.indexDefs),
+        new StorageLocalStorage<C>(childPrefix, this.indexDefs, this.cache.createChild()),
       );
     }
     return this.children.get(path) as StorageLocalStorage<C>;
@@ -250,26 +267,94 @@ export class StorageLocalStorage<
   // ---------------------------------------------------------------------------
 
   /**
-   * Checks whether a document satisfies every field in the filter.
+   * Checks whether a document satisfies a filter.
+   *
+   * Handles top-level logical operators ($and, $or, $not) first via
+   * recursion, then evaluates remaining field-level conditions.
    */
-  private matchesFilter(item: T, filter?: Partial<T>): boolean {
+  private matchesFilter(item: T, filter?: Filter<T>): boolean {
     if (!filter || Object.keys(filter).length === 0) return true;
+
+    // Top-level logical operators.
+    if (filter.$and && !filter.$and.every((f) => this.matchesFilter(item, f))) return false;
+    if (filter.$or && !filter.$or.some((f) => this.matchesFilter(item, f))) return false;
+    if (filter.$not && this.matchesFilter(item, filter.$not)) return false;
+
+    // Field-level conditions (skip logical operator keys).
     for (const [key, value] of Object.entries(filter)) {
+      if (isLogicalKey(key)) continue;
+      if (isOperatorObject(value)) {
+        if (!this.matchesOperators(item[key], value)) return false;
+      } else {
         if (item[key] !== value) return false;
       }
+    }
     return true;
   }
 
+  /**
+   * Evaluate a set of comparison / string operators against a single field value.
+   * All operators must pass for the field to match.
+   */
+  private matchesOperators(fieldValue: any, ops: ComparisonOperators<any>): boolean {
+    if (ops.$eq !== undefined && fieldValue !== ops.$eq) return false;
+    if (ops.$ne !== undefined && fieldValue === ops.$ne) return false;
+    if (ops.$lt !== undefined && !(fieldValue < ops.$lt)) return false;
+    if (ops.$lte !== undefined && !(fieldValue <= ops.$lte)) return false;
+    if (ops.$gt !== undefined && !(fieldValue > ops.$gt)) return false;
+    if (ops.$gte !== undefined && !(fieldValue >= ops.$gte)) return false;
+
+    if (ops.$startsWith !== undefined) {
+      if (typeof fieldValue !== 'string' || !fieldValue.startsWith(ops.$startsWith)) return false;
+    }
+    if (ops.$contains !== undefined) {
+      if (typeof fieldValue !== 'string' || !fieldValue.includes(ops.$contains)) return false;
+    }
+
+    // Field-level $not: invert the enclosed operator set.
+    if (ops.$not !== undefined) {
+      if (this.matchesOperators(fieldValue, ops.$not)) return false;
+    }
+
+    return true;
+  }
+
+  /**
+   * Determine whether candidate documents returned by index resolution still
+   * require full filter verification.
+   */
+  private filterNeedsVerification(
+    filter: Filter<T> | undefined,
+    resolvedFields: string[],
+  ): boolean {
+    if (!filter) return false;
+    const filterKeys = Object.keys(filter);
+    const hasLogicalOps = filterKeys.some(isLogicalKey);
+    return hasLogicalOps
+      || filterKeys.some((k) => !isLogicalKey(k) && !resolvedFields.includes(k));
+  }
+
   /**
    * Collect all [internalKey, document] pairs that match a filter.
    * Uses an index when possible, otherwise falls back to a full scan.
    */
-  private collectMatches(filter?: Partial<T>): Array<[number, T]> {
-    const indexKeys = this.resolveIndexKeys(filter);
-    const keysToScan = indexKeys ?? this.manifest;
+  private collectMatches(filter?: Filter<T>): Array<[number, T]> {
+    const resolution = this.resolveIndexKeys(filter);
     const results: Array<[number, T]> = [];
 
-    for (const key of keysToScan) {
+    if (resolution !== null) {
+      const { keys, resolvedFields } = resolution;
+      const needsVerification = this.filterNeedsVerification(filter, resolvedFields);
+
+      for (const key of keys) {
+        const raw = localStorage.getItem(this.docKey(key));
+        if (raw === null) continue;
+        const doc = JSON.parse(raw) as T;
+        if (needsVerification && !this.matchesFilter(doc, filter)) continue;
+        results.push([key, doc]);
+      }
+    } else {
+      for (const key of this.manifest) {
         const raw = localStorage.getItem(this.docKey(key));
         if (raw === null) continue;
         const doc = JSON.parse(raw) as T;
@@ -277,6 +362,7 @@ export class StorageLocalStorage<
           results.push([key, doc]);
         }
       }
+    }
 
     return results;
   }
@@ -300,82 +386,203 @@ export class StorageLocalStorage<
   // ---------------------------------------------------------------------------
 
   /**
-   * Build the index value string for a given document and set of fields.
-   * Returns `null` if any field is missing from the document.
+   * Build the B+ Tree key for a document and a set of index fields.
+   * - Single-field indexes return the raw field value.
+   * - Compound indexes return an array of raw field values.
+   * Returns `null` if any required field is missing from the document.
    */
-  private buildIndexValue(doc: Record<string, any>, fields: string[]): string | null {
-    const parts: string[] = [];
+  private buildIndexKey(doc: Record<string, any>, fields: string[]): any | null {
+    if (fields.length === 1) {
+      if (!(fields[0] in doc)) return null;
+      return doc[fields[0]];
+    }
+
+    const parts: any[] = [];
     for (const field of fields) {
       if (!(field in doc)) return null;
-      parts.push(String(doc[field]));
+      parts.push(doc[field]);
     }
-    return parts.join(INDEX_KEY_SEP);
+    return parts;
   }
 
   /** Register a document in all applicable indexes. */
   private addToIndexes(internalKey: number, doc: T): void {
     for (const fields of this.indexDefs) {
-      const indexName = fields.join(INDEX_KEY_SEP);
-      const indexValue = this.buildIndexValue(doc, fields);
-      if (indexValue === null) continue;
+      const indexKey = this.buildIndexKey(doc, fields);
+      if (indexKey === null) continue;
 
-      const indexMap = this.indexes.get(indexName)!;
-      let bucket = indexMap.get(indexValue);
-      if (!bucket) {
-        bucket = new Set();
-        indexMap.set(indexValue, bucket);
-      }
-      bucket.add(internalKey);
+      const name = fields.join(INDEX_KEY_SEP);
+      this.cache.insert(name, indexKey, internalKey);
     }
   }
 
   /** Remove a document from all applicable indexes. */
   private removeFromIndexes(internalKey: number, doc: T): void {
     for (const fields of this.indexDefs) {
-      const indexName = fields.join(INDEX_KEY_SEP);
-      const indexValue = this.buildIndexValue(doc, fields);
-      if (indexValue === null) continue;
+      const indexKey = this.buildIndexKey(doc, fields);
+      if (indexKey === null) continue;
 
-      const indexMap = this.indexes.get(indexName)!;
-      const bucket = indexMap.get(indexValue);
-      if (bucket) {
-        bucket.delete(internalKey);
-        if (bucket.size === 0) indexMap.delete(indexValue);
-      }
+      const name = fields.join(INDEX_KEY_SEP);
+      this.cache.delete(name, indexKey, internalKey);
     }
   }
 
   /**
    * Attempt to resolve candidate internal keys from the indexes.
    * Returns `null` if no index can serve the query.
+   *
+   * Supports three resolution strategies:
+   * 1. Equality lookup via B+ Tree `.get()` — O(log n)
+   * 2. Range scan via B+ Tree `.range()` — O(log n + k)
+   * 3. Compound equality — B+ Tree `.get()` with a tuple key
    */
-  private resolveIndexKeys(filter?: Partial<T>): Set<number> | null {
+  private resolveIndexKeys(
+    filter?: Filter<T>,
+  ): { keys: Iterable<number>; resolvedFields: string[] } | null {
     if (!filter) return null;
     const filterKeys = Object.keys(filter);
     if (filterKeys.length === 0) return null;
 
     for (const fields of this.indexDefs) {
-      if (!fields.every((f) => f in filter)) continue;
-
       const indexName = fields.join(INDEX_KEY_SEP);
-      const indexValue = this.buildIndexValue(filter, fields);
-      if (indexValue === null) continue;
 
-      const indexMap = this.indexes.get(indexName)!;
-      const bucket = indexMap.get(indexValue);
-      return bucket ?? new Set();
+      if (fields.length === 1) {
+        // --- Single-field index ---
+        const field = fields[0];
+        if (!(field in filter)) continue;
+
+        const filterValue = (filter as any)[field];
+
+        if (isOperatorObject(filterValue)) {
+          const keys = this.resolveOperatorViaTree(indexName, filterValue);
+          if (keys !== null) return { keys, resolvedFields: [field] };
+          continue;
+        }
+
+        // Plain equality.
+        return { keys: this.cache.get(indexName, filterValue), resolvedFields: [field] };
+      } else {
+        // --- Compound index — all fields must be plain equality ---
+        if (!fields.every((f) => f in filter && !isOperatorObject((filter as any)[f]))) {
+          continue;
+        }
+
+        const tupleKey = fields.map((f) => (filter as any)[f]);
+        return { keys: this.cache.get(indexName, tupleKey), resolvedFields: [...fields] };
+      }
     }
 
     return null;
   }
 
   /**
-   * Rebuild all in-memory index maps by reading every document from
+   * Try to resolve an operator filter against a single-field B+ Tree index.
+   * Returns a flat array of matching internal keys, or null if the
+   * operators can't be efficiently served by the tree.
+   *
+   * Supported acceleration:
+   * - `$eq`         → point lookup via `.get()`
+   * - `$gt/$gte/$lt/$lte` → range scan via `.range()`
+   * - `$startsWith` → converted to a range scan on the prefix
+   * - `$ne`, `$contains`, `$not` → cannot use index, returns null
+   */
+  private resolveOperatorViaTree(
+    indexName: string,
+    ops: ComparisonOperators<any>,
+  ): Iterable<number> | null {
+    // Operators that prevent efficient index use.
+    if (ops.$ne !== undefined || ops.$contains !== undefined || ops.$not !== undefined) return null;
+
+    if (ops.$eq !== undefined) {
+      // If $eq is combined with other operators, this path does not fully
+      // resolve the predicate. Let caller fall back to verification/full scan.
+      if (
+        ops.$gt !== undefined
+        || ops.$gte !== undefined
+        || ops.$lt !== undefined
+        || ops.$lte !== undefined
+        || ops.$startsWith !== undefined
+      ) {
+        return null;
+      }
+      return this.cache.get(indexName, ops.$eq);
+    }
+
+    // $startsWith is converted to a range scan: "abc" → ["abc", "abd").
+    if (ops.$startsWith !== undefined) {
+      const prefix = ops.$startsWith;
+      if (prefix.length === 0) return null;
+      const upper = prefix.slice(0, -1)
+        + String.fromCharCode(prefix.charCodeAt(prefix.length - 1) + 1);
+      const entries = this.cache.range(indexName, prefix, upper, {
+        lowerInclusive: true,
+        upperInclusive: false,
+      });
+      return entries;
+    }
+
+    // Extract range bounds from the remaining operators.
+    // If strict/non-strict variants are both provided, use the stricter bound.
+    let min: any = undefined;
+    let max: any = undefined;
+    let lowerInclusive = true;
+    let upperInclusive = false;
+
+    if (ops.$gt !== undefined && ops.$gte !== undefined) {
+      if (ops.$gt > ops.$gte) {
+        min = ops.$gt;
+        lowerInclusive = false;
+      } else if (ops.$gt < ops.$gte) {
+        min = ops.$gte;
+        lowerInclusive = true;
+      } else {
+        min = ops.$gt;
+        lowerInclusive = false;
+      }
+    } else if (ops.$gt !== undefined) {
+      min = ops.$gt;
+      lowerInclusive = false;
+    } else if (ops.$gte !== undefined) {
+      min = ops.$gte;
+      lowerInclusive = true;
+    }
+
+    if (ops.$lt !== undefined && ops.$lte !== undefined) {
+      if (ops.$lt < ops.$lte) {
+        max = ops.$lt;
+        upperInclusive = false;
+      } else if (ops.$lt > ops.$lte) {
+        max = ops.$lte;
+        upperInclusive = true;
+      } else {
+        max = ops.$lt;
+        upperInclusive = false;
+      }
+    } else if (ops.$lt !== undefined) {
+      max = ops.$lt;
+      upperInclusive = false;
+    } else if (ops.$lte !== undefined) {
+      max = ops.$lte;
+      upperInclusive = true;
+    }
+
+    if (min === undefined && max === undefined) return null;
+    if (min !== undefined && max !== undefined) {
+      if (min > max) return [];
+      if (min === max && (!lowerInclusive || !upperInclusive)) return [];
+    }
+
+    return this.cache.range(indexName, min, max, { lowerInclusive, upperInclusive });
+  }
+
+  /**
+   * Rebuild all in-memory index B+ Trees by reading every document from
    * localStorage. Called only when a cross-tab manifest change is detected.
    */
   private rebuildIndexes(): void {
-    for (const [, indexMap] of this.indexes) {
-      indexMap.clear();
+    for (const fields of this.indexDefs) {
+      const name = fields.join(INDEX_KEY_SEP);
+      this.cache.clearIndex(name);
     }
 
     for (const key of this.manifest) {
@@ -405,6 +612,11 @@ export class StorageLocalStorage<
     return `${this.prefix}${KEY_SEP}${COUNTER_SUFFIX}`;
   }
 
+  /** Build the localStorage key used to persist the mutation version. */
+  private versionKey(): string {
+    return `${this.prefix}${KEY_SEP}${VERSION_SUFFIX}`;
+  }
+
   /**
    * Re-read the manifest from localStorage into memory.
    * Called at the start of every public method so that cross-tab writes
@@ -415,23 +627,41 @@ export class StorageLocalStorage<
    */
   private refreshManifest(): void {
     const raw = localStorage.getItem(this.manifestKey()) ?? '[]';
+    const versionRaw = localStorage.getItem(this.versionKey()) ?? '0';
 
-    if (raw === this.lastManifestRaw) return;
+    if (raw === this.lastManifestRaw && versionRaw === this.lastVersionRaw) return;
 
-    this.lastManifestRaw = raw;
+    let parsedKeys: number[] = [];
+    let parsedOk = true;
 
     try {
-      const keys: number[] = JSON.parse(raw);
-      this.manifest = new Set(keys);
+      parsedKeys = JSON.parse(raw);
     } catch {
+      parsedOk = false;
       this.manifest = new Set();
     }
 
+    if (parsedOk) {
+      this.manifest = new Set(parsedKeys);
+      this.lastManifestRaw = raw;
+    }
+    this.lastVersionRaw = versionRaw;
+
     // Restore the counter from localStorage.
     const counterRaw = localStorage.getItem(this.counterKey());
-    this.nextKey = counterRaw !== null ? Number(counterRaw) : 0;
+    if (counterRaw !== null) {
+      this.nextKey = Number(counterRaw);
+    } else if (this.manifest.size > 0) {
+      let max = -1;
+      for (const key of this.manifest) {
+        if (key > max) max = key;
+      }
+      this.nextKey = max + 1;
+    } else {
+      this.nextKey = 0;
+    }
 
-    // Manifest changed — indexes are potentially stale.
+    // Manifest or version changed — indexes are potentially stale.
     if (this.indexDefs.length > 0) {
       this.rebuildIndexes();
     }
@@ -442,11 +672,16 @@ export class StorageLocalStorage<
    */
   private persistManifest(): void {
     const raw = JSON.stringify([...this.manifest]);
+    const nextVersion = Number(localStorage.getItem(this.versionKey()) ?? '0') + 1;
+    const versionRaw = String(nextVersion);
+
     localStorage.setItem(this.manifestKey(), raw);
     localStorage.setItem(this.counterKey(), String(this.nextKey));
+    localStorage.setItem(this.versionKey(), versionRaw);
 
-    // Keep the cached raw string in sync so the next refreshManifest()
-    // recognises this as "our own write" and skips the rebuild.
+    // Keep cached values in sync so the next refreshManifest() recognises
+    // this as our own write and skips unnecessary rebuild work.
     this.lastManifestRaw = raw;
+    this.lastVersionRaw = versionRaw;
   }
 }

src/storage/storage-memory-synced.ts

@@ -1,4 +1,4 @@
-import { BaseStorage, FindOptions } from './base-storage.js';
+import { BaseStorage, FindOptions, type Filter } from './base-storage.js';
 import { StorageMemory } from './storage-memory.js';
 
 /**
@@ -7,11 +7,17 @@ import { StorageMemory } from './storage-memory.js';
  * All read operations will use system memory - all write operations will use the provided adapter.
  */
 export class StorageMemorySynced<T extends Record<string, any> = Record<string, any>> extends BaseStorage<T> {
+  private isPrimed: boolean;
+  private primePromise: Promise<void> | null;
+
   constructor(
     private inMemoryCache: StorageMemory<T>,
     private store: BaseStorage<T>,
+    isPrimed = false,
   ) {
     super();
+    this.isPrimed = isPrimed;
+    this.primePromise = null;
 
     // Hook into all write operations so that we can sync the In-Memory cache.
     this.store.on('insert', async (payload) => {
@@ -44,6 +50,23 @@ export class StorageMemorySynced<T extends Record<string, any> = Record<string,
     });
   }
 
+  /**
+   * Ensure the in-memory cache has been initialized from the backing store.
+   * This is especially important for derived children, whose caches start empty.
+   */
+  private async ensurePrimed(): Promise<void> {
+    if (this.isPrimed) return;
+    if (!this.primePromise) {
+      this.primePromise = (async () => {
+        await this.inMemoryCache.deleteMany({});
+        const allDocuments = await this.store.find();
+        await this.inMemoryCache.insertMany(allDocuments);
+        this.isPrimed = true;
+      })();
+    }
+    await this.primePromise;
+  }
+
   static async create<T extends Record<string, any>>(store: BaseStorage<T>) {
     // Instantiate in-memory cache and the backing store.
     const inMemoryCache = new StorageMemory<T>();
@@ -58,6 +81,7 @@ export class StorageMemorySynced<T extends Record<string, any> = Record<string,
     }
 
     // Return our instance of this store.
+    memorySyncedStore.isPrimed = true;
     return memorySyncedStore;
   }
 
@@ -65,19 +89,22 @@ export class StorageMemorySynced<T extends Record<string, any> = Record<string,
     await this.store.insertMany(documents);
   }
 
-  async find(filter?: Partial<T>, options?: FindOptions): Promise<T[]> {
+  async find(filter?: Filter<T>, options?: FindOptions): Promise<T[]> {
+    await this.ensurePrimed();
     return await this.inMemoryCache.find(filter, options);
   }
 
   async updateMany(
-    filter: Partial<T>,
+    filter: Filter<T>,
     update: Partial<T>,
-    options: FindOptions = {} as FindOptions
+    options: Partial<FindOptions> = {},
   ): Promise<number> {
+    await this.ensurePrimed();
     return await this.store.updateMany(filter, update, options);
   }
 
-  async deleteMany(filter: Partial<T>, options: FindOptions = {} as FindOptions): Promise<number> {
+  async deleteMany(filter: Filter<T>, options: Partial<FindOptions> = {}): Promise<number> {
+    await this.ensurePrimed();
     return await this.store.deleteMany(filter, options);
   }
 
@@ -85,7 +112,11 @@ export class StorageMemorySynced<T extends Record<string, any> = Record<string,
     const childStore = this.store.deriveChild<C>(path);
     const childMemory = this.inMemoryCache.deriveChild<C>(path);
 
+    if (!(childMemory instanceof StorageMemory)) {
+      throw new Error('Expected derived in-memory cache to be a StorageMemory instance');
+    }
+
     // Create a new synced storage for the child
-    return new StorageMemorySynced<C>(childMemory as StorageMemory<C>, childStore);
+    return new StorageMemorySynced<C>(childMemory, childStore);
   }
 }

src/storage/storage-memory.ts

@@ -1,8 +1,16 @@
-import { BaseStorage, FindOptions, type IndexDefinition } from './base-storage.js';
+import {
+  BaseStorage,
+  FindOptions,
+  type IndexDefinition,
+  type Filter,
+  type ComparisonOperators,
+  isOperatorObject,
+  isLogicalKey,
+} from './base-storage.js';
+import { BaseCache, BTreeCache } from 'src/cache/index.js';
 
 /**
- * Separator used when joining multiple field values into a single index key.
- * Chosen to be unlikely to appear in real field values.
+ * Separator used when joining field names to create the index map key.
  */
 const INDEX_KEY_SEP = '\x00';
 
@@ -27,16 +35,17 @@ function normalizeIndexes(indexes?: IndexDefinition): string[][] {
  *
  * @remarks
  * Documents are keyed internally by an auto-incrementing numeric key.
- * Optional indexes provide O(1) lookups when a query filter matches
- * an index exactly.
+ * Optional indexes are backed by B+ Trees, providing O(log n) equality
+ * lookups and O(log n + k) range queries.
  */
 export class StorageMemory<
   T extends Record<string, any> = Record<string, any>,
 > extends BaseStorage<T> {
   static from<T extends Record<string, any>>(
     indexes?: IndexDefinition,
+    cache?: BaseCache,
   ): StorageMemory<T> {
-    return new StorageMemory<T>(indexes);
+    return new StorageMemory<T>(indexes, cache);
   }
 
   /** Auto-incrementing counter used to generate internal keys. */
@@ -45,13 +54,8 @@ export class StorageMemory<
   /** Primary document store keyed by an opaque internal key. */
   private store: Map<number, T>;
 
-  /**
-   * Secondary index maps.
-   * Outer key  = index name (joined field names).
-   * Inner key  = index value (joined field values from a document).
-   * Inner value = set of internal keys that share this index value.
-   */
-  private indexes: Map<string, Map<string, Set<number>>>;
+  /** Secondary index cache (B-Tree or KV implementation). */
+  private cache: BaseCache;
 
   /** The normalized index definitions supplied at construction time. */
   private indexDefs: string[][];
@@ -59,17 +63,17 @@ export class StorageMemory<
   /** Lazily-created child storage instances. */
   private children: Map<string, StorageMemory<any>>;
 
-  constructor(indexes?: IndexDefinition) {
+  constructor(indexes?: IndexDefinition, cache?: BaseCache) {
     super();
 
     this.store = new Map();
     this.children = new Map();
     this.indexDefs = normalizeIndexes(indexes);
 
-    // Initialise an empty map for each index definition.
-    this.indexes = new Map();
+    this.cache = cache ?? new BTreeCache();
     for (const fields of this.indexDefs) {
-      this.indexes.set(fields.join(INDEX_KEY_SEP), new Map());
+      const name = fields.join(INDEX_KEY_SEP);
+      this.cache.registerIndex(name, fields);
     }
   }
 
@@ -86,7 +90,7 @@ export class StorageMemory<
     }
   }
 
-  async find(filter?: Partial<T>, options?: FindOptions): Promise<T[]> {
+  async find(filter?: Filter<T>, options?: FindOptions): Promise<T[]> {
     let results: T[];
 
     // Attempt to satisfy the query via an index.
@@ -118,7 +122,7 @@ export class StorageMemory<
   }
 
   async updateMany(
-    filter: Partial<T>,
+    filter: Filter<T>,
     update: Partial<T>,
     options: Partial<FindOptions> = {},
   ): Promise<number> {
@@ -147,7 +151,7 @@ export class StorageMemory<
   }
 
   async deleteMany(
-    filter: Partial<T>,
+    filter: Filter<T>,
     options: Partial<FindOptions> = {},
   ): Promise<number> {
     const rowsToDelete = this.collectMatches(filter);
@@ -171,7 +175,7 @@ export class StorageMemory<
 
   deriveChild<C>(path: string): BaseStorage<C> {
     if (!this.children.has(path)) {
-      this.children.set(path, new StorageMemory<C>(this.indexDefs));
+      this.children.set(path, new StorageMemory<C>(this.indexDefs, this.cache.createChild()));
     }
     return this.children.get(path) as StorageMemory<C>;
   }
@@ -181,38 +185,93 @@ export class StorageMemory<
   // ---------------------------------------------------------------------------
 
   /**
-   * Checks whether a document satisfies every field in the filter.
-   * An empty or undefined filter matches everything.
+   * Checks whether a document satisfies a filter.
+   *
+   * Handles top-level logical operators ($and, $or, $not) first via
+   * recursion, then evaluates remaining field-level conditions.
    */
-  private matchesFilter(item: T, filter?: Partial<T>): boolean {
+  private matchesFilter(item: T, filter?: Filter<T>): boolean {
     if (!filter || Object.keys(filter).length === 0) {
       return true;
     }
 
+    // Top-level logical operators.
+    if (filter.$and && !filter.$and.every((f) => this.matchesFilter(item, f))) return false;
+    if (filter.$or && !filter.$or.some((f) => this.matchesFilter(item, f))) return false;
+    if (filter.$not && this.matchesFilter(item, filter.$not)) return false;
+
+    // Field-level conditions (skip logical operator keys).
     for (const [key, value] of Object.entries(filter)) {
-      if (item[key] !== value) {
-        return false;
+      if (isLogicalKey(key)) continue;
+      if (isOperatorObject(value)) {
+        if (!this.matchesOperators(item[key], value)) return false;
+      } else {
+        if (item[key] !== value) return false;
       }
     }
     return true;
   }
 
+  /**
+   * Evaluate a set of comparison / string operators against a single field value.
+   * All operators must pass for the field to match.
+   */
+  private matchesOperators(fieldValue: any, ops: ComparisonOperators<any>): boolean {
+    if (ops.$eq !== undefined && fieldValue !== ops.$eq) return false;
+    if (ops.$ne !== undefined && fieldValue === ops.$ne) return false;
+    if (ops.$lt !== undefined && !(fieldValue < ops.$lt)) return false;
+    if (ops.$lte !== undefined && !(fieldValue <= ops.$lte)) return false;
+    if (ops.$gt !== undefined && !(fieldValue > ops.$gt)) return false;
+    if (ops.$gte !== undefined && !(fieldValue >= ops.$gte)) return false;
+
+    if (ops.$startsWith !== undefined) {
+      if (typeof fieldValue !== 'string' || !fieldValue.startsWith(ops.$startsWith)) return false;
+    }
+    if (ops.$contains !== undefined) {
+      if (typeof fieldValue !== 'string' || !fieldValue.includes(ops.$contains)) return false;
+    }
+
+    // Field-level $not: invert the enclosed operator set.
+    if (ops.$not !== undefined) {
+      if (this.matchesOperators(fieldValue, ops.$not)) return false;
+    }
+
+    return true;
+  }
+
+  /**
+   * Determine whether candidate documents returned by index resolution still
+   * require full filter verification.
+   */
+  private filterNeedsVerification(
+    filter: Filter<T> | undefined,
+    resolvedFields: string[],
+  ): boolean {
+    if (!filter) return false;
+    const filterKeys = Object.keys(filter);
+    const hasLogicalOps = filterKeys.some(isLogicalKey);
+    return hasLogicalOps
+      || filterKeys.some((k) => !isLogicalKey(k) && !resolvedFields.includes(k));
+  }
+
   /**
    * Collect all [internalKey, document] pairs that match a filter.
    * Uses an index when possible, otherwise falls back to a full scan.
    */
-  private collectMatches(filter?: Partial<T>): Array<[number, T]> {
-    const indexKeys = this.resolveIndexKeys(filter);
+  private collectMatches(filter?: Filter<T>): Array<[number, T]> {
+    const resolution = this.resolveIndexKeys(filter);
+
+    if (resolution !== null) {
+      const { keys, resolvedFields } = resolution;
+      const needsVerification = this.filterNeedsVerification(filter, resolvedFields);
 
-    if (indexKeys !== null) {
-      // We have candidate internal keys from the index — fetch and verify.
       const results: Array<[number, T]> = [];
-      for (const key of indexKeys) {
+      for (const key of keys) {
         const doc = this.store.get(key);
-        if (doc && this.matchesFilter(doc, filter)) {
+        if (!doc) continue;
+        if (needsVerification && !this.matchesFilter(doc, filter)) continue;
         results.push([key, doc]);
       }
-      }
       return results;
     }
 
@@ -246,97 +305,216 @@ export class StorageMemory<
   // ---------------------------------------------------------------------------
 
   /**
-   * Build the index value string for a given document and set of fields.
-   * Returns `null` if any of the fields are missing from the document,
-   * since we can't meaningfully index a partial key.
+   * Build the B+ Tree key for a document and a set of index fields.
+   * - Single-field indexes return the raw field value.
+   * - Compound indexes return an array of raw field values.
+   * Returns `null` if any required field is missing from the document.
    */
-  private buildIndexValue(doc: Record<string, any>, fields: string[]): string | null {
-    const parts: string[] = [];
+  private buildIndexKey(doc: Record<string, any>, fields: string[]): any | null {
+    if (fields.length === 1) {
+      if (!(fields[0] in doc)) return null;
+      return doc[fields[0]];
+    }
+
+    const parts: any[] = [];
     for (const field of fields) {
       if (!(field in doc)) return null;
-      parts.push(String(doc[field]));
+      parts.push(doc[field]);
     }
-    return parts.join(INDEX_KEY_SEP);
+    return parts;
   }
 
   /** Register a document in all applicable indexes. */
   private addToIndexes(internalKey: number, doc: T): void {
     for (const fields of this.indexDefs) {
-      const indexName = fields.join(INDEX_KEY_SEP);
-      const indexValue = this.buildIndexValue(doc, fields);
-      if (indexValue === null) continue;
+      const indexKey = this.buildIndexKey(doc, fields);
+      if (indexKey === null) continue;
 
-      const indexMap = this.indexes.get(indexName)!;
-      let bucket = indexMap.get(indexValue);
-      if (!bucket) {
-        bucket = new Set();
-        indexMap.set(indexValue, bucket);
-      }
-      bucket.add(internalKey);
+      const name = fields.join(INDEX_KEY_SEP);
+      this.cache.insert(name, indexKey, internalKey);
     }
   }
 
   /** Remove a document from all applicable indexes. */
   private removeFromIndexes(internalKey: number, doc: T): void {
     for (const fields of this.indexDefs) {
-      const indexName = fields.join(INDEX_KEY_SEP);
-      const indexValue = this.buildIndexValue(doc, fields);
-      if (indexValue === null) continue;
+      const indexKey = this.buildIndexKey(doc, fields);
+      if (indexKey === null) continue;
 
-      const indexMap = this.indexes.get(indexName)!;
-      const bucket = indexMap.get(indexValue);
-      if (bucket) {
-        bucket.delete(internalKey);
-        if (bucket.size === 0) indexMap.delete(indexValue);
-      }
+      const name = fields.join(INDEX_KEY_SEP);
+      this.cache.delete(name, indexKey, internalKey);
     }
   }
 
   /**
-   * Attempt to resolve a set of candidate internal keys from the indexes.
-   * Returns `null` if no index can serve the query.
-   *
-   * An index is used when the filter fields are a superset of (or equal to)
-   * an index's fields — meaning the index value can be fully constructed
-   * from the filter.
+   * Result of an index resolution attempt.
+   * `keys` is an iterable of candidate internal keys.
+   * `resolvedFields` lists the filter fields fully satisfied by the index,
+   * so callers can skip re-verifying those conditions in matchesFilter.
    */
-  private resolveIndexKeys(filter?: Partial<T>): Set<number> | null {
+  private resolveIndexKeys(
+    filter?: Filter<T>,
+  ): { keys: Iterable<number>; resolvedFields: string[] } | null {
     if (!filter) return null;
     const filterKeys = Object.keys(filter);
     if (filterKeys.length === 0) return null;
 
     for (const fields of this.indexDefs) {
-      // Every field in the index must be present in the filter.
-      if (!fields.every((f) => f in filter)) continue;
-
       const indexName = fields.join(INDEX_KEY_SEP);
-      const indexValue = this.buildIndexValue(filter, fields);
-      if (indexValue === null) continue;
 
-      const indexMap = this.indexes.get(indexName)!;
-      const bucket = indexMap.get(indexValue);
-      return bucket ?? new Set();
+      if (fields.length === 1) {
+        // --- Single-field index ---
+        const field = fields[0];
+        if (!(field in filter)) continue;
+
+        const filterValue = (filter as any)[field];
+
+        if (isOperatorObject(filterValue)) {
+          const keys = this.resolveOperatorViaTree(indexName, filterValue);
+          if (keys !== null) return { keys, resolvedFields: [field] };
+          continue;
+        }
+
+        // Plain equality.
+        return { keys: this.cache.get(indexName, filterValue), resolvedFields: [field] };
+      } else {
+        // --- Compound index — all fields must be plain equality ---
+        if (!fields.every((f) => f in filter && !isOperatorObject((filter as any)[f]))) {
+          continue;
+        }
+
+        const tupleKey = fields.map((f) => (filter as any)[f]);
+        return { keys: this.cache.get(indexName, tupleKey), resolvedFields: [...fields] };
+      }
     }
 
     return null;
   }
 
+  /**
+   * Try to resolve an operator filter against a single-field B+ Tree index.
+   * Returns a flat array of matching internal keys, or null if the
+   * operators can't be efficiently served by the tree.
+   *
+   * Supported acceleration:
+   * - `$eq`         → point lookup via `.get()`
+   * - `$gt/$gte/$lt/$lte` → range scan via `.range()`
+   * - `$startsWith` → converted to a range scan on the prefix
+   * - `$ne`, `$contains`, `$not` → cannot use index, returns null
+   */
+  private resolveOperatorViaTree(
+    indexName: string,
+    ops: ComparisonOperators<any>,
+  ): Iterable<number> | null {
+    // Operators that prevent efficient index use.
+    if (ops.$ne !== undefined || ops.$contains !== undefined || ops.$not !== undefined) return null;
+
+    // $eq is a point lookup.
+    if (ops.$eq !== undefined) {
+      // If $eq is combined with other operators, this path does not fully
+      // resolve the predicate. Let caller fall back to verification/full scan.
+      if (
+        ops.$gt !== undefined
+        || ops.$gte !== undefined
+        || ops.$lt !== undefined
+        || ops.$lte !== undefined
+        || ops.$startsWith !== undefined
+      ) {
+        return null;
+      }
+      return this.cache.get(indexName, ops.$eq);
+    }
+
+    // $startsWith is converted to a range scan: "abc" → ["abc", "abd").
+    if (ops.$startsWith !== undefined) {
+      const prefix = ops.$startsWith;
+      if (prefix.length === 0) return null;
+      const upper = prefix.slice(0, -1)
+        + String.fromCharCode(prefix.charCodeAt(prefix.length - 1) + 1);
+      const entries = this.cache.range(indexName, prefix, upper, {
+        lowerInclusive: true,
+        upperInclusive: false,
+      });
+      return entries;
+    }
+
+    // Extract range bounds from the remaining operators.
+    // If strict/non-strict variants are both provided, use the stricter bound.
+    let min: any = undefined;
+    let max: any = undefined;
+    let lowerInclusive = true;
+    let upperInclusive = false;
+
+    if (ops.$gt !== undefined && ops.$gte !== undefined) {
+      if (ops.$gt > ops.$gte) {
+        min = ops.$gt;
+        lowerInclusive = false;
+      } else if (ops.$gt < ops.$gte) {
+        min = ops.$gte;
+        lowerInclusive = true;
+      } else {
+        min = ops.$gt;
+        lowerInclusive = false;
+      }
+    } else if (ops.$gt !== undefined) {
+      min = ops.$gt;
+      lowerInclusive = false;
+    } else if (ops.$gte !== undefined) {
+      min = ops.$gte;
+      lowerInclusive = true;
+    }
+
+    if (ops.$lt !== undefined && ops.$lte !== undefined) {
+      if (ops.$lt < ops.$lte) {
+        max = ops.$lt;
+        upperInclusive = false;
+      } else if (ops.$lt > ops.$lte) {
+        max = ops.$lte;
+        upperInclusive = true;
+      } else {
+        max = ops.$lt;
+        upperInclusive = false;
+      }
+    } else if (ops.$lt !== undefined) {
+      max = ops.$lt;
+      upperInclusive = false;
+    } else if (ops.$lte !== undefined) {
+      max = ops.$lte;
+      upperInclusive = true;
+    }
+
+    if (min === undefined && max === undefined) return null;
+    if (min !== undefined && max !== undefined) {
+      if (min > max) return [];
+      if (min === max && (!lowerInclusive || !upperInclusive)) return [];
+    }
+
+    return this.cache.range(indexName, min, max, { lowerInclusive, upperInclusive });
+  }
+
   /**
    * Try to answer a `find` query entirely through an index.
    * Returns `null` when no index can serve the filter, signalling
    * the caller to fall back to a full scan.
+   *
+   * When the index covers every field in the filter, matchesFilter
+   * is skipped entirely — the B+ Tree has already ensured the
+   * conditions are met.
    */
-  private findViaIndex(filter?: Partial<T>): T[] | null {
-    const keys = this.resolveIndexKeys(filter);
-    if (keys === null) return null;
+  private findViaIndex(filter?: Filter<T>): T[] | null {
+    const resolution = this.resolveIndexKeys(filter);
+    if (resolution === null) return null;
+
+    const { keys, resolvedFields } = resolution;
+    const needsVerification = this.filterNeedsVerification(filter, resolvedFields);
 
     const results: T[] = [];
     for (const key of keys) {
       const doc = this.store.get(key);
-      if (doc && this.matchesFilter(doc, filter)) {
+      if (!doc) continue;
+      if (needsVerification && !this.matchesFilter(doc, filter)) continue;
       results.push(doc);
     }
-    }
     return results;
   }
 }

src/transports/ephemeral-transport.ts

@@ -17,17 +17,17 @@ export class EphemeralTransport {
     return response;
   }
 
-  async receive<T extends ZodType>(url: string, schema: T): Promise<output<T>>;
-  async receive(url: string): Promise<unknown>;
-  async receive(url: string, schema?: ZodType): Promise<unknown> {
+  async receive<T extends ZodType | undefined>(url: string, schema?: T): Promise<T extends undefined ? unknown : output<T>> {
     const transport = await this.transports(url);
     const message = await transport.waitFor('message', () => true);
     transport.disconnect();
 
     if (schema) {
-      return schema.parse(message);
+      // TODO: Figure out how the hell to fix this assertion. It shouldnt be needed, but TS is being a bitch.
+      return schema.parse(message) as T extends undefined ? unknown : output<T>;
     }
 
-    return message;
+    // TODO: Figure out how the hell to fix this assertion. It shouldnt be needed, but TS is being a bitch.
+    return message as T extends undefined ? unknown : output<T>;
   }
 }

src/utils/btree.ts

@@ -0,0 +1,553 @@
+/**
+ * Generic comparator function. Returns negative if a < b, positive if a > b, 0 if equal.
+ */
+export type Comparator<K> = (a: K, b: K) => number;
+
+/**
+ * Options for range queries.
+ */
+export type RangeOptions = {
+  /** Whether the lower bound is inclusive (default: true). */
+  lowerInclusive?: boolean;
+  /** Whether the upper bound is inclusive (default: false). */
+  upperInclusive?: boolean;
+};
+
+/**
+ * A single entry returned by range queries and iteration.
+ */
+export type BPlusTreeEntry<K, V> = {
+  key: K;
+  values: Set<V>;
+};
+
+// ---------------------------------------------------------------------------
+// Node types
+// ---------------------------------------------------------------------------
+
+/**
+ * Internal (non-leaf) node. Stores keys that guide searches and pointers
+ * to child nodes. Does NOT store values — all values live in leaves.
+ */
+class InternalNode<K, V> {
+  keys: K[] = [];
+  children: Array<InternalNode<K, V> | LeafNode<K, V>> = [];
+}
+
+/**
+ * Leaf node. Stores key/value-set pairs and maintains a doubly-linked
+ * list across all leaves for efficient range scans.
+ */
+class LeafNode<K, V> {
+  keys: K[] = [];
+  values: Array<Set<V>> = [];
+  next: LeafNode<K, V> | null = null;
+  prev: LeafNode<K, V> | null = null;
+}
+
+type Node<K, V> = InternalNode<K, V> | LeafNode<K, V>;
+
+function isLeaf<K, V>(node: Node<K, V>): node is LeafNode<K, V> {
+  return node instanceof LeafNode;
+}
+
+// ---------------------------------------------------------------------------
+// Default comparator
+// ---------------------------------------------------------------------------
+
+/**
+ * Default comparator using native `<` / `>` operators.
+ * Works correctly for numbers, strings, and Dates.
+ */
+function defaultComparator<K>(a: K, b: K): number {
+  if (a < b) return -1;
+  if (a > b) return 1;
+  return 0;
+}
+
+// ---------------------------------------------------------------------------
+// B+ Tree
+// ---------------------------------------------------------------------------
+
+/**
+ * In-memory B+ Tree with duplicate-key support.
+ *
+ * Each unique key maps to a `Set<V>`, allowing multiple values to share
+ * the same key (e.g. many documents with the same indexed field value).
+ *
+ * Leaf nodes are linked in a doubly-linked list so range scans are O(k)
+ * after the initial O(log n) descent.
+ *
+ * @typeParam K - Key type (must be comparable via the provided comparator)
+ * @typeParam V - Value type stored in each key's Set
+ */
+export class BPlusTree<K, V> {
+  /** Maximum number of keys per node. A node splits when it exceeds this. */
+  private readonly maxKeys: number;
+
+  /** Minimum number of keys a non-root node must hold after deletion. */
+  private readonly minKeys: number;
+
+  private readonly compare: Comparator<K>;
+
+  private root: Node<K, V>;
+
+  /** Total number of individual values across all keys. */
+  private _size = 0;
+
+  constructor(order = 32, comparator?: Comparator<K>) {
+    if (order < 3) throw new Error('B+ Tree order must be at least 3');
+    this.maxKeys = order - 1;
+    this.minKeys = Math.ceil(order / 2) - 1;
+    this.compare = comparator ?? defaultComparator;
+    this.root = new LeafNode<K, V>();
+  }
+
+  // -------------------------------------------------------------------------
+  // Public API
+  // -------------------------------------------------------------------------
+
+  /** Total number of individual values stored in the tree. */
+  get size(): number {
+    return this._size;
+  }
+
+  /** Remove all entries from the tree. */
+  clear(): void {
+    this.root = new LeafNode<K, V>();
+    this._size = 0;
+  }
+
+  /**
+   * Insert a value under the given key. If the key already exists the
+   * value is added to its Set; otherwise a new key entry is created.
+   */
+  insert(key: K, value: V): void {
+    const leaf = this.findLeaf(key);
+    const idx = this.leafKeyIndex(leaf, key);
+
+    if (idx < leaf.keys.length && this.compare(leaf.keys[idx], key) === 0) {
+      // Key exists — add to its value set.
+      const before = leaf.values[idx].size;
+      leaf.values[idx].add(value);
+      this._size += leaf.values[idx].size - before;
+    } else {
+      // New key — splice into position.
+      leaf.keys.splice(idx, 0, key);
+      leaf.values.splice(idx, 0, new Set([value]));
+      this._size++;
+    }
+
+    // Split if the leaf overflows.
+    if (leaf.keys.length > this.maxKeys) {
+      this.splitLeaf(leaf);
+    }
+  }
+
+  /**
+   * Look up all values associated with the exact key.
+   * Returns `undefined` if the key is not present.
+   */
+  get(key: K): Set<V> | undefined {
+    const leaf = this.findLeaf(key);
+    const idx = this.leafKeyIndex(leaf, key);
+    if (idx < leaf.keys.length && this.compare(leaf.keys[idx], key) === 0) {
+      return leaf.values[idx];
+    }
+    return undefined;
+  }
+
+  /**
+   * Delete a value (or all values) for the given key.
+   *
+   * - If `value` is provided, only that value is removed from the key's Set.
+   *   The key entry is removed when its Set becomes empty.
+   * - If `value` is omitted, the entire key entry (with all values) is removed.
+   *
+   * @returns `true` if something was removed, `false` if the key/value wasn't found.
+   */
+  delete(key: K, value?: V): boolean {
+    const leaf = this.findLeaf(key);
+    const idx = this.leafKeyIndex(leaf, key);
+
+    if (idx >= leaf.keys.length || this.compare(leaf.keys[idx], key) !== 0) {
+      return false;
+    }
+
+    if (value !== undefined) {
+      const set = leaf.values[idx];
+      if (!set.has(value)) return false;
+      set.delete(value);
+      this._size--;
+
+      if (set.size > 0) return true;
+      // Set empty — fall through to remove the key entry entirely.
+    } else {
+      this._size -= leaf.values[idx].size;
+    }
+
+    leaf.keys.splice(idx, 1);
+    leaf.values.splice(idx, 1);
+
+    // Rebalance if needed (skip for root leaf).
+    if (leaf !== this.root && leaf.keys.length < this.minKeys) {
+      this.rebalanceLeaf(leaf);
+    }
+
+    // Shrink tree height if the root internal node has a single child.
+    if (!isLeaf(this.root) && this.root.children.length === 1) {
+      this.root = this.root.children[0];
+    }
+
+    return true;
+  }
+
+  /**
+   * Range query. Returns all entries whose keys fall within `[min, max]`
+   * (bounds configurable via `opts`).
+   *
+   * - Omit `min` for an unbounded lower end.
+   * - Omit `max` for an unbounded upper end.
+   * - Omit both to iterate the entire tree in key order.
+   *
+   * Default bounds: lower inclusive, upper exclusive (half-open interval).
+   */
+  range(
+    min?: K,
+    max?: K,
+    opts?: RangeOptions,
+  ): BPlusTreeEntry<K, V>[] {
+    const lowerInc = opts?.lowerInclusive ?? true;
+    const upperInc = opts?.upperInclusive ?? false;
+
+    const results: BPlusTreeEntry<K, V>[] = [];
+
+    // Find the starting leaf.
+    let leaf: LeafNode<K, V>;
+    let startIdx: number;
+
+    if (min !== undefined) {
+      leaf = this.findLeaf(min);
+      startIdx = this.leafKeyIndex(leaf, min);
+      // Adjust for exclusive lower bound.
+      if (!lowerInc && startIdx < leaf.keys.length && this.compare(leaf.keys[startIdx], min) === 0) {
+        startIdx++;
+      }
+    } else {
+      leaf = this.firstLeaf();
+      startIdx = 0;
+    }
+
+    // Walk the leaf chain collecting matching entries.
+    let currentLeaf: LeafNode<K, V> | null = leaf;
+    let i = startIdx;
+
+    while (currentLeaf) {
+      while (i < currentLeaf.keys.length) {
+        const key = currentLeaf.keys[i];
+
+        if (max !== undefined) {
+          const cmp = this.compare(key, max);
+          if (cmp > 0 || (cmp === 0 && !upperInc)) {
+            return results;
+          }
+        }
+
+        results.push({ key, values: currentLeaf.values[i] });
+        i++;
+      }
+
+      currentLeaf = currentLeaf.next;
+      i = 0;
+    }
+
+    return results;
+  }
+
+  /**
+   * Iterate over all entries in key order.
+   */
+  *entries(): IterableIterator<BPlusTreeEntry<K, V>> {
+    let leaf: LeafNode<K, V> | null = this.firstLeaf();
+    while (leaf) {
+      for (let i = 0; i < leaf.keys.length; i++) {
+        yield { key: leaf.keys[i], values: leaf.values[i] };
+      }
+      leaf = leaf.next;
+    }
+  }
+
+  // -------------------------------------------------------------------------
+  // Tree navigation
+  // -------------------------------------------------------------------------
+
+  /**
+   * Descend to the leaf node that should contain the given key.
+   */
+  private findLeaf(key: K): LeafNode<K, V> {
+    let node: Node<K, V> = this.root;
+    while (!isLeaf(node)) {
+      const internal = node as InternalNode<K, V>;
+      let childIdx = internal.keys.length;
+      for (let i = 0; i < internal.keys.length; i++) {
+        if (this.compare(key, internal.keys[i]) < 0) {
+          childIdx = i;
+          break;
+        }
+      }
+      node = internal.children[childIdx];
+    }
+    return node;
+  }
+
+  /** Get the leftmost leaf in the tree. */
+  private firstLeaf(): LeafNode<K, V> {
+    let node: Node<K, V> = this.root;
+    while (!isLeaf(node)) {
+      node = (node as InternalNode<K, V>).children[0];
+    }
+    return node;
+  }
+
+  /**
+   * Binary search within a leaf for the insertion position of `key`.
+   * Returns the index of the first key >= `key`.
+   */
+  private leafKeyIndex(leaf: LeafNode<K, V>, key: K): number {
+    let lo = 0;
+    let hi = leaf.keys.length;
+    while (lo < hi) {
+      const mid = (lo + hi) >>> 1;
+      if (this.compare(leaf.keys[mid], key) < 0) {
+        lo = mid + 1;
+      } else {
+        hi = mid;
+      }
+    }
+    return lo;
+  }
+
+  // -------------------------------------------------------------------------
+  // Splitting
+  // -------------------------------------------------------------------------
+
+  /**
+   * Split an overflowing leaf node. The right half becomes a new leaf,
+   * and a copy of its first key is promoted to the parent.
+   */
+  private splitLeaf(leaf: LeafNode<K, V>): void {
+    const mid = Math.ceil(leaf.keys.length / 2);
+    const newLeaf = new LeafNode<K, V>();
+
+    newLeaf.keys = leaf.keys.splice(mid);
+    newLeaf.values = leaf.values.splice(mid);
+
+    // Maintain the doubly-linked list.
+    newLeaf.next = leaf.next;
+    newLeaf.prev = leaf;
+    if (leaf.next) leaf.next.prev = newLeaf;
+    leaf.next = newLeaf;
+
+    const promotedKey = newLeaf.keys[0];
+    this.insertIntoParent(leaf, promotedKey, newLeaf);
+  }
+
+  /**
+   * Split an overflowing internal node. The middle key is pushed up
+   * to the parent (not copied — it's removed from this level).
+   */
+  private splitInternal(node: InternalNode<K, V>): void {
+    const mid = Math.floor(node.keys.length / 2);
+    const promotedKey = node.keys[mid];
+
+    const newNode = new InternalNode<K, V>();
+    newNode.keys = node.keys.splice(mid + 1);
+    newNode.children = node.children.splice(mid + 1);
+    node.keys.splice(mid, 1); // remove the promoted key
+
+    this.insertIntoParent(node, promotedKey, newNode);
+  }
+
+  /**
+   * Insert a promoted key and new right child into the parent of `left`.
+   * If `left` is the root, a new root is created.
+   */
+  private insertIntoParent(
+    left: Node<K, V>,
+    key: K,
+    right: Node<K, V>,
+  ): void {
+    if (left === this.root) {
+      const newRoot = new InternalNode<K, V>();
+      newRoot.keys = [key];
+      newRoot.children = [left, right];
+      this.root = newRoot;
+      return;
+    }
+
+    const parent = this.findParent(this.root, left) as InternalNode<K, V>;
+    const idx = parent.children.indexOf(left);
+
+    parent.keys.splice(idx, 0, key);
+    parent.children.splice(idx + 1, 0, right);
+
+    if (parent.keys.length > this.maxKeys) {
+      this.splitInternal(parent);
+    }
+  }
+
+  // -------------------------------------------------------------------------
+  // Rebalancing (deletion)
+  // -------------------------------------------------------------------------
+
+  /**
+   * Rebalance a leaf that has fewer than `minKeys` entries after deletion.
+   * Tries to borrow from a sibling first; if neither sibling can spare
+   * a key, merges with a sibling.
+   */
+  private rebalanceLeaf(leaf: LeafNode<K, V>): void {
+    const parent = this.findParent(this.root, leaf) as InternalNode<K, V>;
+    const idx = parent.children.indexOf(leaf);
+
+    // Try borrowing from the right sibling.
+    if (idx < parent.children.length - 1) {
+      const rightSibling = parent.children[idx + 1] as LeafNode<K, V>;
+      if (rightSibling.keys.length > this.minKeys) {
+        leaf.keys.push(rightSibling.keys.shift()!);
+        leaf.values.push(rightSibling.values.shift()!);
+        parent.keys[idx] = rightSibling.keys[0];
+        return;
+      }
+    }
+
+    // Try borrowing from the left sibling.
+    if (idx > 0) {
+      const leftSibling = parent.children[idx - 1] as LeafNode<K, V>;
+      if (leftSibling.keys.length > this.minKeys) {
+        leaf.keys.unshift(leftSibling.keys.pop()!);
+        leaf.values.unshift(leftSibling.values.pop()!);
+        parent.keys[idx - 1] = leaf.keys[0];
+        return;
+      }
+    }
+
+    // Merge with a sibling.
+    if (idx < parent.children.length - 1) {
+      this.mergeLeaves(leaf, parent.children[idx + 1] as LeafNode<K, V>, parent, idx);
+    } else {
+      this.mergeLeaves(parent.children[idx - 1] as LeafNode<K, V>, leaf, parent, idx - 1);
+    }
+  }
+
+  /**
+   * Merge `right` leaf into `left` leaf and remove the separator key
+   * from the parent.
+   */
+  private mergeLeaves(
+    left: LeafNode<K, V>,
+    right: LeafNode<K, V>,
+    parent: InternalNode<K, V>,
+    separatorIdx: number,
+  ): void {
+    left.keys.push(...right.keys);
+    left.values.push(...right.values);
+
+    // Fix linked list pointers.
+    left.next = right.next;
+    if (right.next) right.next.prev = left;
+
+    // Remove the separator key and right child from the parent.
+    parent.keys.splice(separatorIdx, 1);
+    parent.children.splice(separatorIdx + 1, 1);
+
+    // Recursively rebalance the parent if needed.
+    if (parent !== this.root && parent.keys.length < this.minKeys) {
+      this.rebalanceInternal(parent);
+    }
+  }
+
+  /**
+   * Rebalance an internal node that has too few keys after a merge.
+   */
+  private rebalanceInternal(node: InternalNode<K, V>): void {
+    const parent = this.findParent(this.root, node) as InternalNode<K, V>;
+    const idx = parent.children.indexOf(node);
+
+    // Try borrowing from the right sibling.
+    if (idx < parent.children.length - 1) {
+      const rightSibling = parent.children[idx + 1] as InternalNode<K, V>;
+      if (rightSibling.keys.length > this.minKeys) {
+        node.keys.push(parent.keys[idx]);
+        parent.keys[idx] = rightSibling.keys.shift()!;
+        node.children.push(rightSibling.children.shift()!);
+        return;
+      }
+    }
+
+    // Try borrowing from the left sibling.
+    if (idx > 0) {
+      const leftSibling = parent.children[idx - 1] as InternalNode<K, V>;
+      if (leftSibling.keys.length > this.minKeys) {
+        node.keys.unshift(parent.keys[idx - 1]);
+        parent.keys[idx - 1] = leftSibling.keys.pop()!;
+        node.children.unshift(leftSibling.children.pop()!);
+        return;
+      }
+    }
+
+    // Merge with a sibling.
+    if (idx < parent.children.length - 1) {
+      const rightSibling = parent.children[idx + 1] as InternalNode<K, V>;
+      this.mergeInternal(node, rightSibling, parent, idx);
+    } else {
+      const leftSibling = parent.children[idx - 1] as InternalNode<K, V>;
+      this.mergeInternal(leftSibling, node, parent, idx - 1);
+    }
+  }
+
+  /**
+   * Merge two internal nodes by pulling down the separator key from the
+   * parent and concatenating children.
+   */
+  private mergeInternal(
+    left: InternalNode<K, V>,
+    right: InternalNode<K, V>,
+    parent: InternalNode<K, V>,
+    separatorIdx: number,
+  ): void {
+    left.keys.push(parent.keys[separatorIdx]);
+    left.keys.push(...right.keys);
+    left.children.push(...right.children);
+
+    parent.keys.splice(separatorIdx, 1);
+    parent.children.splice(separatorIdx + 1, 1);
+
+    if (parent !== this.root && parent.keys.length < this.minKeys) {
+      this.rebalanceInternal(parent);
+    }
+  }
+
+  // -------------------------------------------------------------------------
+  // Utilities
+  // -------------------------------------------------------------------------
+
+  /**
+   * Walk the tree from `current` downward to find the parent of `target`.
+   * Returns `null` if `target` is the root or not found.
+   */
+  private findParent(
+    current: Node<K, V>,
+    target: Node<K, V>,
+  ): InternalNode<K, V> | null {
+    if (isLeaf(current)) return null;
+    const internal = current as InternalNode<K, V>;
+
+    for (const child of internal.children) {
+      if (child === target) return internal;
+      const found = this.findParent(child, target);
+      if (found) return found;
+    }
+
+    return null;
+  }
+}

src/utils/index.ts

@@ -1,3 +1,4 @@
 export * from './event-emitter.js';
 export * from './exponential-backoff.js';
 export * from './sse-session.js';
+export * from './btree.js';

tests/storage/storage-regressions.test.ts

@@ -0,0 +1,58 @@
+import { describe, expect, it } from 'vitest';
+
+import { AESKey } from 'src/crypto/aes-key.js';
+
+import { EncryptedStorage } from 'src/storage/encrypted-storage.js';
+import { StorageMemory } from 'src/storage/storage-memory.js';
+import { StorageMemorySynced } from 'src/storage/storage-memory-synced.js';
+
+describe('storage regressions', () => {
+  it('does not treat $eq as fully resolved when mixed with other operators', async () => {
+    const storage = StorageMemory.from<{ age: number }>(['age']);
+    await storage.insertMany([{ age: 25 }, { age: 35 }]);
+
+    const results = await storage.find({ age: { $eq: 25, $gt: 30 } });
+    expect(results).toEqual([]);
+  });
+
+  it('normalizes conflicting lower/upper bounds to strictest constraints', async () => {
+    const storage = StorageMemory.from<{ age: number }>(['age']);
+    await storage.insertMany([{ age: 30 }, { age: 31 }, { age: 32 }]);
+
+    const lower = await storage.find({ age: { $gt: 30, $gte: 30 } });
+    expect(lower.map((d) => d.age).sort((a, b) => a - b)).toEqual([31, 32]);
+
+    const upper = await storage.find({ age: { $lt: 32, $lte: 32 } });
+    expect(upper.map((d) => d.age).sort((a, b) => a - b)).toEqual([30, 31]);
+  });
+
+  it('formats plaintext operator values in encrypted filters', async () => {
+    type Doc = { createdAt: Date; name: string };
+    const key = await AESKey.fromSeed('storage-regression-test-key');
+    const base = StorageMemory.from<Record<string, any>>(['createdAt']);
+    const storage = EncryptedStorage.from<Doc>(base, key, { plaintextKeys: ['createdAt'] });
+
+    await storage.insertOne({
+      createdAt: new Date('2024-01-02T00:00:00.000Z'),
+      name: 'alice',
+    });
+
+    const results = await storage.find({
+      createdAt: { $gte: new Date('2024-01-01T00:00:00.000Z') },
+    });
+    expect(results).toHaveLength(1);
+    expect(results[0].name).toBe('alice');
+  });
+
+  it('primes derived child cache in StorageMemorySynced', async () => {
+    const store = StorageMemory.from<Record<string, any>>();
+    const child = store.deriveChild<{ value: number }>('child');
+    await child.insertOne({ value: 42 });
+
+    const synced = await StorageMemorySynced.create(store);
+    const syncedChild = synced.deriveChild<{ value: number }>('child');
+    const results = await syncedChild.find();
+
+    expect(results).toEqual([{ value: 42 }]);
+  });
+});

tests/utils/btree.test.ts

@@ -0,0 +1,392 @@
+import { describe, it, expect, beforeEach } from 'vitest';
+import { BPlusTree } from '../../src/utils/btree.js';
+
+describe('BPlusTree', () => {
+  let tree: BPlusTree<number, string>;
+
+  beforeEach(() => {
+    tree = new BPlusTree<number, string>();
+  });
+
+  // -------------------------------------------------------------------------
+  // Construction
+  // -------------------------------------------------------------------------
+
+  describe('constructor', () => {
+    it('should create an empty tree', () => {
+      expect(tree.size).toBe(0);
+    });
+
+    it('should reject order < 3', () => {
+      expect(() => new BPlusTree(2)).toThrow('order must be at least 3');
+    });
+  });
+
+  // -------------------------------------------------------------------------
+  // Insert & Get
+  // -------------------------------------------------------------------------
+
+  describe('insert and get', () => {
+    it('should insert and retrieve a single entry', () => {
+      tree.insert(10, 'a');
+      expect(tree.get(10)).toEqual(new Set(['a']));
+      expect(tree.size).toBe(1);
+    });
+
+    it('should handle multiple distinct keys', () => {
+      tree.insert(10, 'a');
+      tree.insert(20, 'b');
+      tree.insert(5, 'c');
+      expect(tree.get(10)).toEqual(new Set(['a']));
+      expect(tree.get(20)).toEqual(new Set(['b']));
+      expect(tree.get(5)).toEqual(new Set(['c']));
+      expect(tree.size).toBe(3);
+    });
+
+    it('should return undefined for missing keys', () => {
+      tree.insert(10, 'a');
+      expect(tree.get(99)).toBeUndefined();
+    });
+
+    it('should accumulate duplicate keys into a Set', () => {
+      tree.insert(10, 'a');
+      tree.insert(10, 'b');
+      tree.insert(10, 'c');
+      expect(tree.get(10)).toEqual(new Set(['a', 'b', 'c']));
+      expect(tree.size).toBe(3);
+    });
+
+    it('should not double-count duplicate values for the same key', () => {
+      tree.insert(10, 'a');
+      tree.insert(10, 'a');
+      expect(tree.get(10)).toEqual(new Set(['a']));
+      expect(tree.size).toBe(1);
+    });
+  });
+
+  // -------------------------------------------------------------------------
+  // Delete
+  // -------------------------------------------------------------------------
+
+  describe('delete', () => {
+    it('should delete a specific value from a key', () => {
+      tree.insert(10, 'a');
+      tree.insert(10, 'b');
+      expect(tree.delete(10, 'a')).toBe(true);
+      expect(tree.get(10)).toEqual(new Set(['b']));
+      expect(tree.size).toBe(1);
+    });
+
+    it('should remove the key entry when its last value is deleted', () => {
+      tree.insert(10, 'a');
+      expect(tree.delete(10, 'a')).toBe(true);
+      expect(tree.get(10)).toBeUndefined();
+      expect(tree.size).toBe(0);
+    });
+
+    it('should delete all values for a key when value is omitted', () => {
+      tree.insert(10, 'a');
+      tree.insert(10, 'b');
+      expect(tree.delete(10)).toBe(true);
+      expect(tree.get(10)).toBeUndefined();
+      expect(tree.size).toBe(0);
+    });
+
+    it('should return false for non-existent key', () => {
+      expect(tree.delete(99)).toBe(false);
+    });
+
+    it('should return false for non-existent value', () => {
+      tree.insert(10, 'a');
+      expect(tree.delete(10, 'z')).toBe(false);
+      expect(tree.size).toBe(1);
+    });
+  });
+
+  // -------------------------------------------------------------------------
+  // Range queries
+  // -------------------------------------------------------------------------
+
+  describe('range', () => {
+    beforeEach(() => {
+      for (let i = 0; i < 100; i++) {
+        tree.insert(i, `v${i}`);
+      }
+    });
+
+    it('should return all entries when no bounds given', () => {
+      const result = tree.range();
+      expect(result.length).toBe(100);
+      expect(result[0].key).toBe(0);
+      expect(result[99].key).toBe(99);
+    });
+
+    it('should return entries in key order', () => {
+      const keys = tree.range().map((e) => e.key);
+      for (let i = 1; i < keys.length; i++) {
+        expect(keys[i]).toBeGreaterThan(keys[i - 1]);
+      }
+    });
+
+    it('should respect lower bound (inclusive by default)', () => {
+      const result = tree.range(50);
+      expect(result.length).toBe(50);
+      expect(result[0].key).toBe(50);
+    });
+
+    it('should respect upper bound (exclusive by default)', () => {
+      const result = tree.range(undefined, 10);
+      expect(result.length).toBe(10);
+      expect(result[result.length - 1].key).toBe(9);
+    });
+
+    it('should support inclusive upper bound', () => {
+      const result = tree.range(undefined, 10, { upperInclusive: true });
+      expect(result.length).toBe(11);
+      expect(result[result.length - 1].key).toBe(10);
+    });
+
+    it('should support exclusive lower bound', () => {
+      const result = tree.range(50, undefined, { lowerInclusive: false });
+      expect(result.length).toBe(49);
+      expect(result[0].key).toBe(51);
+    });
+
+    it('should handle combined bounds', () => {
+      const result = tree.range(20, 30);
+      expect(result.length).toBe(10);
+      expect(result[0].key).toBe(20);
+      expect(result[result.length - 1].key).toBe(29);
+    });
+
+    it('should return empty array for no-result range', () => {
+      const result = tree.range(200, 300);
+      expect(result).toEqual([]);
+    });
+
+    it('should return empty for inverted bounds', () => {
+      const result = tree.range(50, 10);
+      expect(result).toEqual([]);
+    });
+  });
+
+  // -------------------------------------------------------------------------
+  // Edge cases
+  // -------------------------------------------------------------------------
+
+  describe('edge cases', () => {
+    it('should handle get on empty tree', () => {
+      expect(tree.get(1)).toBeUndefined();
+    });
+
+    it('should handle range on empty tree', () => {
+      expect(tree.range()).toEqual([]);
+      expect(tree.range(1, 2)).toEqual([]);
+    });
+
+    it('should handle delete on empty tree', () => {
+      expect(tree.delete(1)).toBe(false);
+    });
+
+    it('should handle insert-then-delete-all back to empty', () => {
+      for (let i = 0; i < 50; i++) {
+        tree.insert(i, `v${i}`);
+      }
+      for (let i = 0; i < 50; i++) {
+        expect(tree.delete(i, `v${i}`)).toBe(true);
+      }
+      expect(tree.size).toBe(0);
+      expect(tree.range()).toEqual([]);
+      // Verify we can still insert after emptying.
+      tree.insert(1, 'new');
+      expect(tree.get(1)).toEqual(new Set(['new']));
+    });
+  });
+
+  // -------------------------------------------------------------------------
+  // Clear
+  // -------------------------------------------------------------------------
+
+  describe('clear', () => {
+    it('should reset the tree to empty', () => {
+      for (let i = 0; i < 100; i++) tree.insert(i, `v${i}`);
+      expect(tree.size).toBe(100);
+      tree.clear();
+      expect(tree.size).toBe(0);
+      expect(tree.get(0)).toBeUndefined();
+      expect(tree.range()).toEqual([]);
+    });
+  });
+
+  // -------------------------------------------------------------------------
+  // Entries iterator
+  // -------------------------------------------------------------------------
+
+  describe('entries', () => {
+    it('should yield all entries in key order', () => {
+      tree.insert(30, 'c');
+      tree.insert(10, 'a');
+      tree.insert(20, 'b');
+
+      const result = [...tree.entries()];
+      expect(result.map((e) => e.key)).toEqual([10, 20, 30]);
+    });
+
+    it('should yield nothing for empty tree', () => {
+      expect([...tree.entries()]).toEqual([]);
+    });
+  });
+
+  // -------------------------------------------------------------------------
+  // Large dataset
+  // -------------------------------------------------------------------------
+
+  describe('large dataset', () => {
+    const N = 10_000;
+
+    it('should correctly store and retrieve N items', () => {
+      for (let i = 0; i < N; i++) {
+        tree.insert(i, `v${i}`);
+      }
+      expect(tree.size).toBe(N);
+
+      // Spot-check some values.
+      expect(tree.get(0)).toEqual(new Set(['v0']));
+      expect(tree.get(N - 1)).toEqual(new Set([`v${N - 1}`]));
+      expect(tree.get(Math.floor(N / 2))).toEqual(new Set([`v${Math.floor(N / 2)}`]));
+    });
+
+    it('should produce correct range results on large dataset', () => {
+      for (let i = 0; i < N; i++) {
+        tree.insert(i, `v${i}`);
+      }
+
+      const result = tree.range(5000, 5010);
+      expect(result.length).toBe(10);
+      expect(result[0].key).toBe(5000);
+      expect(result[9].key).toBe(5009);
+    });
+
+    it('should survive inserting and deleting many items', () => {
+      for (let i = 0; i < N; i++) {
+        tree.insert(i, `v${i}`);
+      }
+
+      // Delete the first half.
+      for (let i = 0; i < N / 2; i++) {
+        expect(tree.delete(i, `v${i}`)).toBe(true);
+      }
+
+      expect(tree.size).toBe(N / 2);
+      expect(tree.get(0)).toBeUndefined();
+      expect(tree.get(N / 2)).toEqual(new Set([`v${N / 2}`]));
+
+      // Remaining range should start at N/2.
+      const remaining = tree.range();
+      expect(remaining.length).toBe(N / 2);
+      expect(remaining[0].key).toBe(N / 2);
+    });
+  });
+
+  // -------------------------------------------------------------------------
+  // Custom comparator
+  // -------------------------------------------------------------------------
+
+  describe('custom comparator', () => {
+    it('should support reverse ordering', () => {
+      const reverseTree = new BPlusTree<number, string>(32, (a, b) => b - a);
+      reverseTree.insert(1, 'a');
+      reverseTree.insert(2, 'b');
+      reverseTree.insert(3, 'c');
+
+      const entries = [...reverseTree.entries()];
+      expect(entries.map((e) => e.key)).toEqual([3, 2, 1]);
+    });
+  });
+
+  // -------------------------------------------------------------------------
+  // Node splitting (small order to force splits)
+  // -------------------------------------------------------------------------
+
+  describe('node splitting with small order', () => {
+    let smallTree: BPlusTree<number, string>;
+
+    beforeEach(() => {
+      smallTree = new BPlusTree<number, string>(4);
+    });
+
+    it('should handle splits correctly', () => {
+      // Order 4 means max 3 keys per node — splits after the 4th insert.
+      for (let i = 0; i < 20; i++) {
+        smallTree.insert(i, `v${i}`);
+      }
+      expect(smallTree.size).toBe(20);
+
+      // All values should be retrievable.
+      for (let i = 0; i < 20; i++) {
+        expect(smallTree.get(i)).toEqual(new Set([`v${i}`]));
+      }
+    });
+
+    it('should maintain sorted order after many splits', () => {
+      // Insert in random order to stress split logic.
+      const values = Array.from({ length: 50 }, (_, i) => i);
+      for (let i = values.length - 1; i > 0; i--) {
+        const j = Math.floor(Math.random() * (i + 1));
+        [values[i], values[j]] = [values[j], values[i]];
+      }
+
+      for (const v of values) {
+        smallTree.insert(v, `v${v}`);
+      }
+
+      const entries = [...smallTree.entries()];
+      const keys = entries.map((e) => e.key);
+      expect(keys).toEqual([...keys].sort((a, b) => a - b));
+    });
+
+    it('should handle delete with merging at small order', () => {
+      for (let i = 0; i < 20; i++) {
+        smallTree.insert(i, `v${i}`);
+      }
+
+      // Delete enough to trigger merges.
+      for (let i = 0; i < 15; i++) {
+        expect(smallTree.delete(i, `v${i}`)).toBe(true);
+      }
+
+      expect(smallTree.size).toBe(5);
+
+      // Remaining keys should be intact.
+      for (let i = 15; i < 20; i++) {
+        expect(smallTree.get(i)).toEqual(new Set([`v${i}`]));
+      }
+    });
+  });
+
+  // -------------------------------------------------------------------------
+  // String keys
+  // -------------------------------------------------------------------------
+
+  describe('string keys', () => {
+    it('should work with string keys using default comparator', () => {
+      const strTree = new BPlusTree<string, number>();
+      strTree.insert('banana', 1);
+      strTree.insert('apple', 2);
+      strTree.insert('cherry', 3);
+
+      const entries = [...strTree.entries()];
+      expect(entries.map((e) => e.key)).toEqual(['apple', 'banana', 'cherry']);
+      expect(strTree.get('banana')).toEqual(new Set([1]));
+    });
+
+    it('should support string range queries', () => {
+      const strTree = new BPlusTree<string, number>();
+      const words = ['apple', 'banana', 'cherry', 'date', 'elderberry', 'fig'];
+      words.forEach((w, i) => strTree.insert(w, i));
+
+      const result = strTree.range('banana', 'elderberry');
+      expect(result.map((e) => e.key)).toEqual(['banana', 'cherry', 'date']);
+    });
+  });
+});