diff --git a/benchmarks/storage.ts b/benchmarks/storage.ts
index 2460d90..3e75c7e 100644
--- a/benchmarks/storage.ts
+++ b/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
@@ -161,9 +162,19 @@ 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 — range queries on age use B+ Tree.
-  const indexedWithAge = StorageMemory.from<Doc>(['id', 'name', 'age']);
-  await benchmarkStorage('StorageMemory (indexed: id,name,age)', indexedWithAge, docs, { hasAgeIndex: true });
+  // 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']);
diff --git a/package.json b/package.json
index ae99315..b680ce1 100644
--- a/package.json
+++ b/package.json
@@ -6,7 +6,9 @@
   "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",
diff --git a/src/cache/b-tree-cache.ts b/src/cache/b-tree-cache.ts
new file mode 100644
index 0000000..ec937fc
--- /dev/null
+++ b/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;
+  }
+}
+
diff --git a/src/cache/base-cache.ts b/src/cache/base-cache.ts
new file mode 100644
index 0000000..6f17d7e
--- /dev/null
+++ b/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;
+}
+
diff --git a/src/cache/index.ts b/src/cache/index.ts
new file mode 100644
index 0000000..8eff9b0
--- /dev/null
+++ b/src/cache/index.ts
@@ -0,0 +1,4 @@
+export * from './base-cache.js';
+export * from './b-tree-cache.js';
+export * from './kv-cache.js';
+
diff --git a/src/cache/kv-cache.ts b/src/cache/kv-cache.ts
new file mode 100644
index 0000000..059f067
--- /dev/null
+++ b/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);
+  }
+}
+
diff --git a/src/storage/base-storage.ts b/src/storage/base-storage.ts
index 909816b..26ddc3f 100644
--- a/src/storage/base-storage.ts
+++ b/src/storage/base-storage.ts
@@ -188,7 +188,7 @@ export abstract class BaseStorage<
    */
   abstract deleteMany(
     filter: Filter<T>,
-    options: Partial<FindOptions>,
+    options?: Partial<FindOptions>,
   ): Promise<number>;
 
   /**
diff --git a/src/storage/encrypted-storage.ts b/src/storage/encrypted-storage.ts
index 6ac5b21..e85ce64 100644
--- a/src/storage/encrypted-storage.ts
+++ b/src/storage/encrypted-storage.ts
@@ -3,7 +3,14 @@ import { Packr } from 'msgpackr';
 import { AESKey } from 'src/crypto/aes-key.js';
 import { Bytes } from 'src/crypto/bytes.js';
 
-import { BaseStorage, type FindOptions, type Filter, isOperatorObject, isLogicalKey } from './base-storage.js';
+import {
+  BaseStorage,
+  type ComparisonOperators,
+  type FindOptions,
+  type Filter,
+  isOperatorObject,
+  isLogicalKey,
+} from './base-storage.js';
 
 import { encodeExtendedJsonObject, decodeExtendedJsonObject } from 'src/utils/ext-json.js';
 
@@ -269,7 +276,7 @@ export class EncryptedStorage<
       if (this.plaintextKeys.has(key)) {
         // Plaintext field — pass through (including operator objects).
         result[key] = isOperatorObject(value)
-          ? value
+          ? this.formatOperatorValuesForStorage(value)
           : this.formatValueForEncryption(value);
       } else if (isOperatorObject(value)) {
         // Encrypted field with an operator — not supported.
@@ -306,6 +313,24 @@ export class EncryptedStorage<
     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
   // ---------------------------------------------------------------------------
diff --git a/src/storage/storage-localstorage.ts b/src/storage/storage-localstorage.ts
index 259c5c3..87d9eb3 100644
--- a/src/storage/storage-localstorage.ts
+++ b/src/storage/storage-localstorage.ts
@@ -7,7 +7,7 @@ import {
   isOperatorObject,
   isLogicalKey,
 } from './base-storage.js';
-import { BPlusTree, type BPlusTreeEntry } from 'src/utils/btree.js';
+import { BaseCache, BTreeCache } from 'src/cache/index.js';
 
 /**
  * Key prefix separator used to namespace documents within localStorage.
@@ -26,6 +26,13 @@ const MANIFEST_SUFFIX = '__keys__';
  */
 const COUNTER_SUFFIX = '__next__';
 
+/**
+ * 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.
  */
@@ -43,18 +50,6 @@ function normalizeIndexes(indexes?: IndexDefinition): string[][] {
   return indexes as string[][];
 }
 
-/**
- * Comparator for compound index keys (arrays of raw values).
- */
-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;
-}
-
 /**
  * Implementation of BaseStorage using the browser's localStorage API.
  *
@@ -80,8 +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);
   }
 
   /**
@@ -100,16 +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 indexes backed by B+ Trees.
-   * Map key = index name (joined field names).
-   * Map value = B+ Tree mapping index keys to sets of internal document keys.
-   */
-  private indexes: Map<string, BPlusTree<any, number>>;
+  /** Secondary index cache (B-Tree or KV implementation). */
+  private cache: BaseCache;
 
   /** Lazily-created child storage instances. */
   private children: Map<string, StorageLocalStorage<any>>;
@@ -117,20 +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) {
       const name = fields.join(INDEX_KEY_SEP);
-      const comparator = fields.length > 1 ? tupleCompare : undefined;
-      this.indexes.set(name, new BPlusTree<any, number>(32, comparator));
+      this.cache.registerIndex(name, fields);
     }
 
     // Bootstrap from localStorage.
     this.lastManifestRaw = '';
+    this.lastVersionRaw = '';
     this.manifest = new Set();
     this.nextKey = 0;
     this.refreshManifest();
@@ -162,10 +156,7 @@ export class StorageLocalStorage<
 
     if (resolution !== null) {
       const { keys, resolvedFields } = resolution;
-      const filterKeys = filter ? Object.keys(filter) : [];
-      const hasLogicalOps = filterKeys.some(isLogicalKey);
-      const needsVerification = hasLogicalOps
-        || filterKeys.some((k) => !isLogicalKey(k) && !resolvedFields.includes(k));
+      const needsVerification = this.filterNeedsVerification(filter, resolvedFields);
 
       results = [];
       for (const key of keys) {
@@ -265,7 +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>;
@@ -328,6 +319,21 @@ export class StorageLocalStorage<
     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.
@@ -338,10 +344,7 @@ export class StorageLocalStorage<
 
     if (resolution !== null) {
       const { keys, resolvedFields } = resolution;
-      const filterKeys = filter ? Object.keys(filter) : [];
-      const hasLogicalOps = filterKeys.some(isLogicalKey);
-      const needsVerification = hasLogicalOps
-        || filterKeys.some((k) => !isLogicalKey(k) && !resolvedFields.includes(k));
+      const needsVerification = this.filterNeedsVerification(filter, resolvedFields);
 
       for (const key of keys) {
         const raw = localStorage.getItem(this.docKey(key));
@@ -409,7 +412,7 @@ export class StorageLocalStorage<
       if (indexKey === null) continue;
 
       const name = fields.join(INDEX_KEY_SEP);
-      this.indexes.get(name)!.insert(indexKey, internalKey);
+      this.cache.insert(name, indexKey, internalKey);
     }
   }
 
@@ -420,7 +423,7 @@ export class StorageLocalStorage<
       if (indexKey === null) continue;
 
       const name = fields.join(INDEX_KEY_SEP);
-      this.indexes.get(name)!.delete(indexKey, internalKey);
+      this.cache.delete(name, indexKey, internalKey);
     }
   }
 
@@ -442,7 +445,6 @@ export class StorageLocalStorage<
 
     for (const fields of this.indexDefs) {
       const indexName = fields.join(INDEX_KEY_SEP);
-      const btree = this.indexes.get(indexName)!;
 
       if (fields.length === 1) {
         // --- Single-field index ---
@@ -452,13 +454,13 @@ export class StorageLocalStorage<
         const filterValue = (filter as any)[field];
 
         if (isOperatorObject(filterValue)) {
-          const keys = this.resolveOperatorViaTree(btree, filterValue);
+          const keys = this.resolveOperatorViaTree(indexName, filterValue);
           if (keys !== null) return { keys, resolvedFields: [field] };
           continue;
         }
 
         // Plain equality.
-        return { keys: btree.get(filterValue) ?? [], resolvedFields: [field] };
+        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]))) {
@@ -466,7 +468,7 @@ export class StorageLocalStorage<
         }
 
         const tupleKey = fields.map((f) => (filter as any)[f]);
-        return { keys: btree.get(tupleKey) ?? [], resolvedFields: [...fields] };
+        return { keys: this.cache.get(indexName, tupleKey), resolvedFields: [...fields] };
       }
     }
 
@@ -485,14 +487,25 @@ export class StorageLocalStorage<
    * - `$ne`, `$contains`, `$not` → cannot use index, returns null
    */
   private resolveOperatorViaTree(
-    btree: BPlusTree<any, number>,
+    indexName: string,
     ops: ComparisonOperators<any>,
   ): Iterable<number> | null {
     // Operators that prevent efficient index use.
     if (ops.$ne !== undefined || ops.$contains !== undefined || ops.$not !== undefined) return null;
 
     if (ops.$eq !== undefined) {
-      return btree.get(ops.$eq) ?? [];
+      // 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").
@@ -501,42 +514,65 @@ export class StorageLocalStorage<
       if (prefix.length === 0) return null;
       const upper = prefix.slice(0, -1)
         + String.fromCharCode(prefix.charCodeAt(prefix.length - 1) + 1);
-      const entries = btree.range(prefix, upper, {
+      const entries = this.cache.range(indexName, prefix, upper, {
         lowerInclusive: true,
         upperInclusive: false,
       });
-      return this.flattenEntryKeys(entries);
+      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.$gt !== undefined) { min = ops.$gt; lowerInclusive = false; }
-    if (ops.$gte !== undefined) { min = ops.$gte; lowerInclusive = true; }
-    if (ops.$lt !== undefined) { max = ops.$lt; upperInclusive = false; }
-    if (ops.$lte !== undefined) { max = ops.$lte; upperInclusive = true; }
+    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;
-
-    const entries = btree.range(min, max, { lowerInclusive, upperInclusive });
-    return this.flattenEntryKeys(entries);
-  }
-
-  /**
-   * Flatten B+ Tree range results into a flat array of internal keys.
-   * Uses an array instead of a Set — no hash overhead, no deduplication
-   * needed because each internal key only appears under one index key.
-   */
-  private flattenEntryKeys(entries: BPlusTreeEntry<any, number>[]): number[] {
-    const result: number[] = [];
-    for (const entry of entries) {
-      for (const key of entry.values) {
-        result.push(key);
-      }
+    if (min !== undefined && max !== undefined) {
+      if (min > max) return [];
+      if (min === max && (!lowerInclusive || !upperInclusive)) return [];
     }
-    return result;
+
+    return this.cache.range(indexName, min, max, { lowerInclusive, upperInclusive });
   }
 
   /**
@@ -544,8 +580,9 @@ export class StorageLocalStorage<
    * localStorage. Called only when a cross-tab manifest change is detected.
    */
   private rebuildIndexes(): void {
-    for (const [, btree] of this.indexes) {
-      btree.clear();
+    for (const fields of this.indexDefs) {
+      const name = fields.join(INDEX_KEY_SEP);
+      this.cache.clearIndex(name);
     }
 
     for (const key of this.manifest) {
@@ -575,6 +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
@@ -585,23 +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();
     }
@@ -612,11 +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;
   }
 }
diff --git a/src/storage/storage-memory-synced.ts b/src/storage/storage-memory-synced.ts
index 3f6b072..2172e2e 100644
--- a/src/storage/storage-memory-synced.ts
+++ b/src/storage/storage-memory-synced.ts
@@ -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;
   }
 
@@ -66,26 +90,33 @@ export class StorageMemorySynced<T extends Record<string, any> = Record<string,
   }
 
   async find(filter?: Filter<T>, options?: FindOptions): Promise<T[]> {
+    await this.ensurePrimed();
     return await this.inMemoryCache.find(filter, options);
   }
 
   async updateMany(
     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: Filter<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);
   }
 
   deriveChild<C extends Record<string, any>>(path: string): BaseStorage<C> {
     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);
   }
 }
diff --git a/src/storage/storage-memory.ts b/src/storage/storage-memory.ts
index 413727a..46a7823 100644
--- a/src/storage/storage-memory.ts
+++ b/src/storage/storage-memory.ts
@@ -7,7 +7,7 @@ import {
   isOperatorObject,
   isLogicalKey,
 } from './base-storage.js';
-import { BPlusTree, type BPlusTreeEntry } from 'src/utils/btree.js';
+import { BaseCache, BTreeCache } from 'src/cache/index.js';
 
 /**
  * Separator used when joining field names to create the index map key.
@@ -30,19 +30,6 @@ function normalizeIndexes(indexes?: IndexDefinition): string[][] {
   return indexes as string[][];
 }
 
-/**
- * Comparator for compound index keys (arrays of raw values).
- * Compares element-by-element using native `<` / `>` operators.
- */
-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;
-}
-
 /**
  * Implementation of BaseStore using Memory as the storage backend.
  *
@@ -56,8 +43,9 @@ export class StorageMemory<
 > 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. */
@@ -66,12 +54,8 @@ export class StorageMemory<
   /** Primary document store keyed by an opaque internal key. */
   private store: Map<number, T>;
 
-  /**
-   * Secondary indexes backed by B+ Trees.
-   * Map key = index name (joined field names).
-   * Map value = B+ Tree mapping index keys to sets of internal document keys.
-   */
-  private indexes: Map<string, BPlusTree<any, number>>;
+  /** Secondary index cache (B-Tree or KV implementation). */
+  private cache: BaseCache;
 
   /** The normalized index definitions supplied at construction time. */
   private indexDefs: string[][];
@@ -79,19 +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);
 
-    // Create a B+ Tree for each index definition.
-    this.indexes = new Map();
+    this.cache = cache ?? new BTreeCache();
     for (const fields of this.indexDefs) {
       const name = fields.join(INDEX_KEY_SEP);
-      const comparator = fields.length > 1 ? tupleCompare : undefined;
-      this.indexes.set(name, new BPlusTree<any, number>(32, comparator));
+      this.cache.registerIndex(name, fields);
     }
   }
 
@@ -193,7 +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>;
   }
@@ -257,6 +239,21 @@ export class StorageMemory<
     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.
@@ -266,10 +263,7 @@ export class StorageMemory<
 
     if (resolution !== null) {
       const { keys, resolvedFields } = resolution;
-      const filterKeys = filter ? Object.keys(filter) : [];
-      const hasLogicalOps = filterKeys.some(isLogicalKey);
-      const needsVerification = hasLogicalOps
-        || filterKeys.some((k) => !isLogicalKey(k) && !resolvedFields.includes(k));
+      const needsVerification = this.filterNeedsVerification(filter, resolvedFields);
 
       const results: Array<[number, T]> = [];
       for (const key of keys) {
@@ -337,7 +331,7 @@ export class StorageMemory<
       if (indexKey === null) continue;
 
       const name = fields.join(INDEX_KEY_SEP);
-      this.indexes.get(name)!.insert(indexKey, internalKey);
+      this.cache.insert(name, indexKey, internalKey);
     }
   }
 
@@ -348,7 +342,7 @@ export class StorageMemory<
       if (indexKey === null) continue;
 
       const name = fields.join(INDEX_KEY_SEP);
-      this.indexes.get(name)!.delete(indexKey, internalKey);
+      this.cache.delete(name, indexKey, internalKey);
     }
   }
 
@@ -367,7 +361,6 @@ export class StorageMemory<
 
     for (const fields of this.indexDefs) {
       const indexName = fields.join(INDEX_KEY_SEP);
-      const btree = this.indexes.get(indexName)!;
 
       if (fields.length === 1) {
         // --- Single-field index ---
@@ -377,13 +370,13 @@ export class StorageMemory<
         const filterValue = (filter as any)[field];
 
         if (isOperatorObject(filterValue)) {
-          const keys = this.resolveOperatorViaTree(btree, filterValue);
+          const keys = this.resolveOperatorViaTree(indexName, filterValue);
           if (keys !== null) return { keys, resolvedFields: [field] };
           continue;
         }
 
         // Plain equality.
-        return { keys: btree.get(filterValue) ?? [], resolvedFields: [field] };
+        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]))) {
@@ -391,7 +384,7 @@ export class StorageMemory<
         }
 
         const tupleKey = fields.map((f) => (filter as any)[f]);
-        return { keys: btree.get(tupleKey) ?? [], resolvedFields: [...fields] };
+        return { keys: this.cache.get(indexName, tupleKey), resolvedFields: [...fields] };
       }
     }
 
@@ -410,7 +403,7 @@ export class StorageMemory<
    * - `$ne`, `$contains`, `$not` → cannot use index, returns null
    */
   private resolveOperatorViaTree(
-    btree: BPlusTree<any, number>,
+    indexName: string,
     ops: ComparisonOperators<any>,
   ): Iterable<number> | null {
     // Operators that prevent efficient index use.
@@ -418,7 +411,18 @@ export class StorageMemory<
 
     // $eq is a point lookup.
     if (ops.$eq !== undefined) {
-      return btree.get(ops.$eq) ?? [];
+      // 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").
@@ -427,43 +431,65 @@ export class StorageMemory<
       if (prefix.length === 0) return null;
       const upper = prefix.slice(0, -1)
         + String.fromCharCode(prefix.charCodeAt(prefix.length - 1) + 1);
-      const entries = btree.range(prefix, upper, {
+      const entries = this.cache.range(indexName, prefix, upper, {
         lowerInclusive: true,
         upperInclusive: false,
       });
-      return this.flattenEntryKeys(entries);
+      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.$gt !== undefined) { min = ops.$gt; lowerInclusive = false; }
-    if (ops.$gte !== undefined) { min = ops.$gte; lowerInclusive = true; }
-    if (ops.$lt !== undefined) { max = ops.$lt; upperInclusive = false; }
-    if (ops.$lte !== undefined) { max = ops.$lte; upperInclusive = true; }
+    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;
-
-    const entries = btree.range(min, max, { lowerInclusive, upperInclusive });
-    return this.flattenEntryKeys(entries);
-  }
-
-  /**
-   * Flatten B+ Tree range results into a flat array of internal keys.
-   * Uses an array instead of a Set — no hash overhead, no deduplication
-   * needed because each internal key only appears under one index key.
-   */
-  private flattenEntryKeys(entries: BPlusTreeEntry<any, number>[]): number[] {
-    const result: number[] = [];
-    for (const entry of entries) {
-      for (const key of entry.values) {
-        result.push(key);
-      }
+    if (min !== undefined && max !== undefined) {
+      if (min > max) return [];
+      if (min === max && (!lowerInclusive || !upperInclusive)) return [];
     }
-    return result;
+
+    return this.cache.range(indexName, min, max, { lowerInclusive, upperInclusive });
   }
 
   /**
@@ -480,13 +506,7 @@ export class StorageMemory<
     if (resolution === null) return null;
 
     const { keys, resolvedFields } = resolution;
-    const filterKeys = filter ? Object.keys(filter) : [];
-
-    // Logical operators ($and/$or/$not) are never resolved by the index,
-    // and any unresolved field conditions also require verification.
-    const hasLogicalOps = filterKeys.some(isLogicalKey);
-    const needsVerification = hasLogicalOps
-      || filterKeys.some((k) => !isLogicalKey(k) && !resolvedFields.includes(k));
+    const needsVerification = this.filterNeedsVerification(filter, resolvedFields);
 
     const results: T[] = [];
     for (const key of keys) {
diff --git a/tests/storage/storage-regressions.test.ts b/tests/storage/storage-regressions.test.ts
new file mode 100644
index 0000000..fa5a0f1
--- /dev/null
+++ b/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 }]);
+  });
+});