diff --git a/QUICKSTART.md b/QUICKSTART.md
index 4f11e27..319b5be 100644
--- a/QUICKSTART.md
+++ b/QUICKSTART.md
@@ -1,21 +1,21 @@
-# Quick Start Guide for @network/sdk
+# Quick Start Guide for @debros/network-ts-sdk
 
 ## 5-Minute Setup
 
 ### 1. Install
 
 ```bash
-npm install @network/sdk
+npm install @debros/network-ts-sdk
 ```
 
 ### 2. Create a Client
 
 ```typescript
-import { createClient } from "@network/sdk";
+import { createClient } from "@debros/network-ts-sdk";
 
 const client = createClient({
   baseURL: "http://localhost:6001",
-  apiKey: "ak_your_api_key:default", // Get from gateway
+  apiKey: "ak_your_api_key:namespace", // Get from gateway
 });
 ```
 
@@ -62,7 +62,7 @@ make run-gateway
 # Terminal 3: Run E2E tests
 cd ../network-ts-sdk
 export GATEWAY_BASE_URL=http://localhost:6001
-export GATEWAY_API_KEY=ak_RsJJXoENynk_5jTJEeM4wJKx:default
+export GATEWAY_API_KEY=ak_your_api_key:default
 pnpm run test:e2e
 ```
 
@@ -124,7 +124,7 @@ await client.db.transaction([
 
 ### Error Handling
 ```typescript
-import { SDKError } from "@network/sdk";
+import { SDKError } from "@debros/network-ts-sdk";
 
 try {
   await client.db.query("SELECT * FROM invalid_table");
@@ -148,7 +148,7 @@ const msg: Message = await subscription.onMessage((m) => m);
 
 1. Read the full [README.md](./README.md)
 2. Explore [tests/e2e/](./tests/e2e/) for examples
-3. Check [IMPLEMENTATION_SUMMARY.md](./IMPLEMENTATION_SUMMARY.md) for architecture
+3. Explore [examples/](./examples/) for runnable code samples
 
 ## Troubleshooting
 
diff --git a/README.md b/README.md
index 8399735..6774611 100644
--- a/README.md
+++ b/README.md
@@ -388,6 +388,197 @@ const client = createClient({
 });
 ```
 
+### Cache Operations
+
+The SDK provides a distributed cache client backed by Olric. Data is organized into distributed maps (dmaps).
+
+#### Put a Value
+
+```typescript
+// Put with optional TTL
+await client.cache.put("sessions", "user:alice", { role: "admin" }, "1h");
+```
+
+#### Get a Value
+
+```typescript
+// Returns null on cache miss (not an error)
+const result = await client.cache.get("sessions", "user:alice");
+if (result) {
+  console.log(result.value); // { role: "admin" }
+}
+```
+
+#### Delete a Value
+
+```typescript
+await client.cache.delete("sessions", "user:alice");
+```
+
+#### Multi-Get
+
+```typescript
+const results = await client.cache.multiGet("sessions", [
+  "user:alice",
+  "user:bob",
+]);
+// Returns Map<string, any | null> — null for misses
+results.forEach((value, key) => {
+  console.log(key, value);
+});
+```
+
+#### Scan Keys
+
+```typescript
+// Scan all keys in a dmap, optionally matching a regex
+const scan = await client.cache.scan("sessions", "user:.*");
+console.log(scan.keys); // ["user:alice", "user:bob"]
+console.log(scan.count); // 2
+```
+
+#### Health Check
+
+```typescript
+const health = await client.cache.health();
+console.log(health.status); // "ok"
+```
+
+### Storage (IPFS)
+
+Upload, pin, and retrieve files from decentralized IPFS storage.
+
+#### Upload a File
+
+```typescript
+// Browser
+const fileInput = document.querySelector('input[type="file"]');
+const file = fileInput.files[0];
+const result = await client.storage.upload(file, file.name);
+console.log(result.cid); // "Qm..."
+
+// Node.js
+import { readFileSync } from "fs";
+const buffer = readFileSync("image.jpg");
+const result = await client.storage.upload(buffer, "image.jpg", { pin: true });
+```
+
+#### Retrieve Content
+
+```typescript
+// Get as ReadableStream
+const stream = await client.storage.get(cid);
+const reader = stream.getReader();
+while (true) {
+  const { done, value } = await reader.read();
+  if (done) break;
+  // Process chunk
+}
+
+// Get full Response (for headers like content-length)
+const response = await client.storage.getBinary(cid);
+const contentLength = response.headers.get("content-length");
+```
+
+#### Pin / Unpin / Status
+
+```typescript
+// Pin an existing CID
+await client.storage.pin("QmExampleCid", "my-file");
+
+// Check pin status
+const status = await client.storage.status("QmExampleCid");
+console.log(status.status); // "pinned", "pinning", "queued", "unpinned", "error"
+
+// Unpin
+await client.storage.unpin("QmExampleCid");
+```
+
+### Serverless Functions (WASM)
+
+Invoke WebAssembly serverless functions deployed on the network.
+
+```typescript
+// Configure functions namespace
+const client = createClient({
+  baseURL: "http://localhost:6001",
+  apiKey: "ak_your_key:namespace",
+  functionsConfig: {
+    namespace: "my-namespace",
+  },
+});
+
+// Invoke a function with typed input/output
+interface PushInput {
+  token: string;
+  message: string;
+}
+interface PushOutput {
+  success: boolean;
+  messageId: string;
+}
+
+const result = await client.functions.invoke<PushInput, PushOutput>(
+  "send-push",
+  { token: "device-token", message: "Hello!" }
+);
+console.log(result.messageId);
+```
+
+### Vault (Distributed Secrets)
+
+The vault client provides Shamir-split secret storage across guardian nodes. Secrets are split into shares, distributed to guardians, and reconstructed only when enough shares are collected (quorum).
+
+```typescript
+const client = createClient({
+  baseURL: "http://localhost:6001",
+  apiKey: "ak_your_key:namespace",
+  vaultConfig: {
+    guardians: [
+      { address: "10.0.0.1", port: 8443 },
+      { address: "10.0.0.2", port: 8443 },
+      { address: "10.0.0.3", port: 8443 },
+    ],
+    identityHex: "your-identity-hex",
+  },
+});
+
+// Store a secret (Shamir-split across guardians)
+const data = new TextEncoder().encode("my-secret-data");
+const storeResult = await client.vault.store("api-key", data, 1);
+console.log(storeResult.quorumMet); // true if enough guardians ACKed
+
+// Retrieve and reconstruct a secret
+const retrieved = await client.vault.retrieve("api-key");
+console.log(new TextDecoder().decode(retrieved.data)); // "my-secret-data"
+
+// List all secrets for this identity
+const secrets = await client.vault.list();
+console.log(secrets.secrets);
+
+// Delete a secret from all guardians
+await client.vault.delete("api-key");
+```
+
+### Wallet-Based Authentication
+
+For wallet-based auth (challenge-response flow):
+
+```typescript
+// 1. Request a challenge
+const challenge = await client.auth.challenge();
+
+// 2. Sign the challenge with your wallet (external)
+const signature = await wallet.signMessage(challenge.message);
+
+// 3. Verify signature and get JWT
+const session = await client.auth.verify(challenge.id, signature);
+console.log(session.token);
+
+// 4. Get an API key for long-lived access
+const apiKey = await client.auth.getApiKey();
+```
+
 ## Error Handling
 
 The SDK throws `SDKError` for all errors:
diff --git a/package.json b/package.json
index bbd9301..c50ade6 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@debros/network-ts-sdk",
-  "version": "0.6.2",
+  "version": "0.7.0",
   "description": "TypeScript SDK for DeBros Network Gateway - Database, PubSub, Cache, Storage, and more",
   "type": "module",
   "main": "./dist/index.js",
@@ -23,7 +23,12 @@
     "wasm",
     "serverless",
     "distributed",
-    "gateway"
+    "gateway",
+    "vault",
+    "secrets",
+    "shamir",
+    "encryption",
+    "guardian"
   ],
   "repository": {
     "type": "git",
@@ -53,6 +58,8 @@
     "release:gh": "npm publish --registry=https://npm.pkg.github.com"
   },
   "dependencies": {
+    "@noble/ciphers": "^0.5.3",
+    "@noble/hashes": "^1.4.0",
     "isomorphic-ws": "^5.0.0"
   },
   "devDependencies": {
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 491a319..6007fa2 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -8,6 +8,12 @@ importers:
 
   .:
     dependencies:
+      '@noble/ciphers':
+        specifier: ^0.5.3
+        version: 0.5.3
+      '@noble/hashes':
+        specifier: ^1.4.0
+        version: 1.8.0
       isomorphic-ws:
         specifier: ^5.0.0
         version: 5.0.0(ws@8.18.3)
@@ -419,6 +425,13 @@ packages:
   '@jridgewell/trace-mapping@0.3.31':
     resolution: {integrity: sha512-zzNR+SdQSDJzc8joaeP8QQoCQr8NuYx2dIIytl1QeBEZHJ9uW6hebsrYgbz8hJwUQao3TWCMtmfV8Nu1twOLAw==}
 
+  '@noble/ciphers@0.5.3':
+    resolution: {integrity: sha512-B0+6IIHiqEs3BPMT0hcRmHvEj2QHOLu+uwt+tqDDeVd0oyVzh7BPrDcPjRnV1PV/5LaknXJJQvOuRGR0zQJz+w==}
+
+  '@noble/hashes@1.8.0':
+    resolution: {integrity: sha512-jCs9ldd7NwzpgXDIf6P3+NrHh9/sD6CQdxHyjQI+h/6rDNo88ypBxxz45UDuZHz9r3tNz7N/VInSVoVdtXEI4A==}
+    engines: {node: ^14.21.3 || >=16}
+
   '@nodelib/fs.scandir@2.1.5':
     resolution: {integrity: sha512-vq24Bq3ym5HEQm2NKCr3yXDwjc7vTsEThRDnkp2DK9p1uqLR+DHurm/NOTo0KG7HYHU7eppKZj3MyqYuMBf62g==}
     engines: {node: '>= 8'}
@@ -1848,6 +1861,10 @@ snapshots:
       '@jridgewell/resolve-uri': 3.1.2
       '@jridgewell/sourcemap-codec': 1.5.5
 
+  '@noble/ciphers@0.5.3': {}
+
+  '@noble/hashes@1.8.0': {}
+
   '@nodelib/fs.scandir@2.1.5':
     dependencies:
       '@nodelib/fs.stat': 2.0.5
diff --git a/src/index.ts b/src/index.ts
index 0ee1839..415c494 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -6,12 +6,14 @@ import { NetworkClient } from "./network/client";
 import { CacheClient } from "./cache/client";
 import { StorageClient } from "./storage/client";
 import { FunctionsClient, FunctionsClientConfig } from "./functions/client";
+import { VaultClient } from "./vault/client";
 import { WSClientConfig } from "./core/ws";
 import {
   StorageAdapter,
   MemoryStorage,
   LocalStorageAdapter,
 } from "./auth/types";
+import type { VaultConfig } from "./vault/types";
 
 export interface ClientConfig extends Omit<HttpClientConfig, "fetch"> {
   apiKey?: string;
@@ -25,6 +27,8 @@ export interface ClientConfig extends Omit<HttpClientConfig, "fetch"> {
    * Use this to trigger gateway failover at the application layer.
    */
   onNetworkError?: NetworkErrorCallback;
+  /** Configuration for the vault (distributed secrets store). */
+  vaultConfig?: VaultConfig;
 }
 
 export interface Client {
@@ -35,6 +39,7 @@ export interface Client {
   cache: CacheClient;
   storage: StorageClient;
   functions: FunctionsClient;
+  vault: VaultClient | null;
 }
 
 export function createClient(config: ClientConfig): Client {
@@ -68,6 +73,9 @@ export function createClient(config: ClientConfig): Client {
   const cache = new CacheClient(httpClient);
   const storage = new StorageClient(httpClient);
   const functions = new FunctionsClient(httpClient, config.functionsConfig);
+  const vault = config.vaultConfig
+    ? new VaultClient(config.vaultConfig)
+    : null;
 
   return {
     auth,
@@ -77,6 +85,7 @@ export function createClient(config: ClientConfig): Client {
     cache,
     storage,
     functions,
+    vault,
   };
 }
 
@@ -133,3 +142,60 @@ export type {
 } from "./storage/client";
 export type { FunctionsClientConfig } from "./functions/client";
 export type * from "./functions/types";
+// Vault module
+export { VaultClient } from "./vault/client";
+export { AuthClient as VaultAuthClient } from "./vault/auth";
+export { GuardianClient, GuardianError } from "./vault/transport";
+export { fanOut, fanOutIndexed, withTimeout, withRetry } from "./vault/transport";
+export { adaptiveThreshold, writeQuorum } from "./vault/quorum";
+export {
+  encrypt,
+  decrypt,
+  encryptString,
+  decryptString,
+  serializeEncrypted,
+  deserializeEncrypted,
+  encryptAndSerialize,
+  deserializeAndDecrypt,
+  encryptedToHex,
+  encryptedFromHex,
+  encryptedToBase64,
+  encryptedFromBase64,
+  generateKey,
+  generateNonce,
+  clearKey,
+  isValidEncryptedData,
+  KEY_SIZE,
+  NONCE_SIZE,
+  TAG_SIZE,
+  deriveKeyHKDF,
+  shamirSplit,
+  shamirCombine,
+} from "./vault";
+export type {
+  VaultConfig,
+  SecretMeta,
+  StoreResult,
+  RetrieveResult,
+  ListResult,
+  DeleteResult,
+  GuardianResult as VaultGuardianResult,
+  EncryptedData,
+  SerializedEncryptedData,
+  ShamirShare,
+  GuardianEndpoint,
+  GuardianErrorCode,
+  GuardianInfo,
+  GuardianHealthResponse,
+  GuardianStatusResponse,
+  PushResponse,
+  PullResponse,
+  StoreSecretResponse,
+  GetSecretResponse,
+  DeleteSecretResponse,
+  ListSecretsResponse,
+  SecretEntry,
+  GuardianChallengeResponse,
+  GuardianSessionResponse,
+  FanOutResult,
+} from "./vault";
diff --git a/src/vault/auth.ts b/src/vault/auth.ts
new file mode 100644
index 0000000..c991a20
--- /dev/null
+++ b/src/vault/auth.ts
@@ -0,0 +1,98 @@
+import { GuardianClient } from './transport/guardian';
+import type { GuardianEndpoint } from './transport/types';
+
+/**
+ * Handles challenge-response authentication with guardian nodes.
+ * Caches session tokens per guardian endpoint.
+ *
+ * Auth flow:
+ * 1. POST /v2/vault/auth/challenge with identity → get {nonce, created_ns, tag}
+ * 2. POST /v2/vault/auth/session with identity + challenge fields → get session token
+ * 3. Use session token as X-Session-Token header for V2 requests
+ *
+ * The session token format is: `<identity_hex>:<expiry_ns>:<tag_hex>`
+ */
+export class AuthClient {
+  private sessions = new Map<string, { token: string; expiryNs: number }>();
+  private identityHex: string;
+  private timeoutMs: number;
+
+  constructor(identityHex: string, timeoutMs = 10_000) {
+    this.identityHex = identityHex;
+    this.timeoutMs = timeoutMs;
+  }
+
+  /**
+   * Authenticate with a guardian and cache the session token.
+   * Returns a GuardianClient with the session token set.
+   */
+  async authenticate(endpoint: GuardianEndpoint): Promise<GuardianClient> {
+    const key = `${endpoint.address}:${endpoint.port}`;
+    const cached = this.sessions.get(key);
+
+    // Check if we have a valid cached session (with 30s safety margin)
+    if (cached) {
+      const nowNs = Date.now() * 1_000_000;
+      if (cached.expiryNs > nowNs + 30_000_000_000) {
+        const client = new GuardianClient(endpoint, this.timeoutMs);
+        client.setSessionToken(cached.token);
+        return client;
+      }
+      // Expired, remove
+      this.sessions.delete(key);
+    }
+
+    const client = new GuardianClient(endpoint, this.timeoutMs);
+
+    // Step 1: Request challenge
+    const challenge = await client.requestChallenge(this.identityHex);
+
+    // Step 2: Exchange for session
+    const session = await client.createSession(
+      this.identityHex,
+      challenge.nonce,
+      challenge.created_ns,
+      challenge.tag,
+    );
+
+    // Build token string: identity:expiry_ns:tag
+    const token = `${session.identity}:${session.expiry_ns}:${session.tag}`;
+    client.setSessionToken(token);
+
+    // Cache
+    this.sessions.set(key, { token, expiryNs: session.expiry_ns });
+
+    return client;
+  }
+
+  /**
+   * Authenticate with multiple guardians in parallel.
+   * Returns authenticated GuardianClients for all that succeed.
+   */
+  async authenticateAll(endpoints: GuardianEndpoint[]): Promise<{ client: GuardianClient; endpoint: GuardianEndpoint }[]> {
+    const results = await Promise.allSettled(
+      endpoints.map(async (ep) => {
+        const client = await this.authenticate(ep);
+        return { client, endpoint: ep };
+      }),
+    );
+
+    const authenticated: { client: GuardianClient; endpoint: GuardianEndpoint }[] = [];
+    for (const r of results) {
+      if (r.status === 'fulfilled') {
+        authenticated.push(r.value);
+      }
+    }
+    return authenticated;
+  }
+
+  /** Clear all cached sessions. */
+  clearSessions(): void {
+    this.sessions.clear();
+  }
+
+  /** Get the identity hex string. */
+  getIdentityHex(): string {
+    return this.identityHex;
+  }
+}
diff --git a/src/vault/client.ts b/src/vault/client.ts
new file mode 100644
index 0000000..028658e
--- /dev/null
+++ b/src/vault/client.ts
@@ -0,0 +1,197 @@
+import { AuthClient } from './auth';
+import type { GuardianClient } from './transport/guardian';
+import { withTimeout, withRetry } from './transport/fanout';
+import { split, combine } from './crypto/shamir';
+import type { Share } from './crypto/shamir';
+import { adaptiveThreshold, writeQuorum } from './quorum';
+import type {
+  VaultConfig,
+  StoreResult,
+  RetrieveResult,
+  ListResult,
+  DeleteResult,
+  GuardianResult,
+} from './types';
+
+const PULL_TIMEOUT_MS = 10_000;
+
+/**
+ * High-level client for the orama-vault distributed secrets store.
+ *
+ * Handles:
+ * - Authentication with guardian nodes
+ * - Shamir split/combine for data distribution
+ * - Quorum-based writes and reads
+ * - V2 CRUD operations (store, retrieve, list, delete)
+ */
+export class VaultClient {
+  private config: VaultConfig;
+  private auth: AuthClient;
+
+  constructor(config: VaultConfig) {
+    this.config = config;
+    this.auth = new AuthClient(config.identityHex, config.timeoutMs);
+  }
+
+  /**
+   * Store a secret across guardian nodes using Shamir splitting.
+   *
+   * @param name - Secret name (alphanumeric, _, -, max 128 chars)
+   * @param data - Secret data to store
+   * @param version - Monotonic version number (must be > previous)
+   */
+  async store(name: string, data: Uint8Array, version: number): Promise<StoreResult> {
+    const guardians = this.config.guardians;
+    const n = guardians.length;
+    const k = adaptiveThreshold(n);
+
+    // Shamir split the data
+    const shares = split(data, n, k);
+
+    // Authenticate and push to all guardians
+    const authed = await this.auth.authenticateAll(guardians);
+
+    const results = await Promise.allSettled(
+      authed.map(async ({ client, endpoint }, _i) => {
+        // Find the share for this guardian's index
+        const guardianIdx = guardians.indexOf(endpoint);
+        const share = shares[guardianIdx];
+        if (!share) throw new Error('share index out of bounds');
+
+        // Encode share as [x:1byte][y:rest]
+        const shareBytes = new Uint8Array(1 + share.y.length);
+        shareBytes[0] = share.x;
+        shareBytes.set(share.y, 1);
+
+        return withRetry(() => client.putSecret(name, shareBytes, version));
+      }),
+    );
+
+    // Wipe shares
+    for (const share of shares) {
+      share.y.fill(0);
+    }
+
+    const guardianResults: GuardianResult[] = authed.map(({ endpoint }, i) => {
+      const ep = `${endpoint.address}:${endpoint.port}`;
+      const r = results[i]!;
+      if (r.status === 'fulfilled') {
+        return { endpoint: ep, success: true };
+      }
+      return { endpoint: ep, success: false, error: (r.reason as Error).message };
+    });
+
+    const ackCount = results.filter((r) => r.status === 'fulfilled').length;
+    const failCount = results.filter((r) => r.status === 'rejected').length;
+    const w = writeQuorum(n);
+
+    return {
+      ackCount,
+      totalContacted: authed.length,
+      failCount,
+      quorumMet: ackCount >= w,
+      guardianResults,
+    };
+  }
+
+  /**
+   * Retrieve and reconstruct a secret from guardian nodes.
+   *
+   * @param name - Secret name
+   */
+  async retrieve(name: string): Promise<RetrieveResult> {
+    const guardians = this.config.guardians;
+    const n = guardians.length;
+    const k = adaptiveThreshold(n);
+
+    // Authenticate and pull from all guardians
+    const authed = await this.auth.authenticateAll(guardians);
+
+    const pullResults = await Promise.allSettled(
+      authed.map(async ({ client }) => {
+        const resp = await withTimeout(client.getSecret(name), PULL_TIMEOUT_MS);
+        const shareBytes = resp.share;
+        if (shareBytes.length < 2) throw new Error('Share too short');
+        return {
+          x: shareBytes[0]!,
+          y: shareBytes.slice(1),
+        } as Share;
+      }),
+    );
+
+    const shares: Share[] = [];
+    for (const r of pullResults) {
+      if (r.status === 'fulfilled') {
+        shares.push(r.value);
+      }
+    }
+
+    if (shares.length < k) {
+      throw new Error(
+        `Not enough shares: collected ${shares.length} of ${k} required (contacted ${authed.length} guardians)`,
+      );
+    }
+
+    // Reconstruct
+    const data = combine(shares);
+
+    // Wipe collected shares
+    for (const share of shares) {
+      share.y.fill(0);
+    }
+
+    return {
+      data,
+      sharesCollected: shares.length,
+    };
+  }
+
+  /**
+   * List all secrets for this identity.
+   * Queries the first reachable guardian (metadata is replicated).
+   */
+  async list(): Promise<ListResult> {
+    const guardians = this.config.guardians;
+    const authed = await this.auth.authenticateAll(guardians);
+
+    if (authed.length === 0) {
+      throw new Error('No guardians reachable');
+    }
+
+    // Query first authenticated guardian
+    const resp = await authed[0]!.client.listSecrets();
+    return { secrets: resp.secrets };
+  }
+
+  /**
+   * Delete a secret from all guardian nodes.
+   *
+   * @param name - Secret name to delete
+   */
+  async delete(name: string): Promise<DeleteResult> {
+    const guardians = this.config.guardians;
+    const n = guardians.length;
+
+    const authed = await this.auth.authenticateAll(guardians);
+
+    const results = await Promise.allSettled(
+      authed.map(async ({ client }) => {
+        return withRetry(() => client.deleteSecret(name));
+      }),
+    );
+
+    const ackCount = results.filter((r) => r.status === 'fulfilled').length;
+    const w = writeQuorum(n);
+
+    return {
+      ackCount,
+      totalContacted: authed.length,
+      quorumMet: ackCount >= w,
+    };
+  }
+
+  /** Clear all cached auth sessions. */
+  clearSessions(): void {
+    this.auth.clearSessions();
+  }
+}
diff --git a/src/vault/crypto/aes.ts b/src/vault/crypto/aes.ts
new file mode 100644
index 0000000..ff349ac
--- /dev/null
+++ b/src/vault/crypto/aes.ts
@@ -0,0 +1,271 @@
+/**
+ * AES-256-GCM Encryption
+ *
+ * Implements authenticated encryption using AES-256 in Galois/Counter Mode.
+ * Uses @noble/ciphers for platform-agnostic, audited cryptographic operations.
+ *
+ * Features:
+ * - Authenticated encryption (confidentiality + integrity)
+ * - 256-bit keys for strong security
+ * - 96-bit nonces (randomly generated)
+ * - 128-bit authentication tags
+ *
+ * Security considerations:
+ * - Never reuse a nonce with the same key
+ * - Nonces are randomly generated and prepended to ciphertext
+ * - Authentication tags are verified before decryption
+ */
+
+import { gcm } from '@noble/ciphers/aes';
+import { randomBytes } from '@noble/ciphers/webcrypto';
+import { bytesToHex, hexToBytes, concatBytes } from '@noble/hashes/utils';
+
+/**
+ * Size constants
+ */
+export const KEY_SIZE = 32; // 256 bits
+export const NONCE_SIZE = 12; // 96 bits (recommended for GCM)
+export const TAG_SIZE = 16; // 128 bits
+
+/**
+ * Encrypted data structure
+ */
+export interface EncryptedData {
+  /** Ciphertext including authentication tag */
+  ciphertext: Uint8Array;
+  /** Nonce used for encryption */
+  nonce: Uint8Array;
+  /** Additional authenticated data (optional) */
+  aad?: Uint8Array;
+}
+
+/**
+ * Serialized encrypted data (nonce prepended to ciphertext)
+ */
+export interface SerializedEncryptedData {
+  /** Combined nonce + ciphertext + tag */
+  data: Uint8Array;
+  /** Additional authenticated data (optional) */
+  aad?: Uint8Array;
+}
+
+/**
+ * Encrypts data using AES-256-GCM
+ */
+export function encrypt(
+  plaintext: Uint8Array,
+  key: Uint8Array,
+  aad?: Uint8Array
+): EncryptedData {
+  validateKey(key);
+
+  const nonce = randomBytes(NONCE_SIZE);
+  const cipher = gcm(key, nonce, aad);
+  const ciphertext = cipher.encrypt(plaintext);
+
+  return {
+    ciphertext,
+    nonce,
+    aad,
+  };
+}
+
+/**
+ * Decrypts data using AES-256-GCM
+ */
+export function decrypt(encryptedData: EncryptedData, key: Uint8Array): Uint8Array {
+  validateKey(key);
+  validateNonce(encryptedData.nonce);
+
+  const cipher = gcm(key, encryptedData.nonce, encryptedData.aad);
+
+  try {
+    return cipher.decrypt(encryptedData.ciphertext);
+  } catch (error) {
+    throw new Error('Decryption failed: invalid ciphertext or authentication tag');
+  }
+}
+
+/**
+ * Encrypts a string message
+ */
+export function encryptString(
+  message: string,
+  key: Uint8Array,
+  aad?: Uint8Array
+): EncryptedData {
+  const plaintext = new TextEncoder().encode(message);
+  try {
+    return encrypt(plaintext, key, aad);
+  } finally {
+    plaintext.fill(0);
+  }
+}
+
+/**
+ * Decrypts to a string message
+ */
+export function decryptString(encryptedData: EncryptedData, key: Uint8Array): string {
+  const plaintext = decrypt(encryptedData, key);
+  try {
+    return new TextDecoder().decode(plaintext);
+  } finally {
+    plaintext.fill(0);
+  }
+}
+
+/**
+ * Serializes encrypted data (prepends nonce to ciphertext)
+ */
+export function serialize(encryptedData: EncryptedData): SerializedEncryptedData {
+  const data = concatBytes(encryptedData.nonce, encryptedData.ciphertext);
+
+  return {
+    data,
+    aad: encryptedData.aad,
+  };
+}
+
+/**
+ * Deserializes encrypted data
+ */
+export function deserialize(serialized: SerializedEncryptedData): EncryptedData {
+  if (serialized.data.length < NONCE_SIZE + TAG_SIZE) {
+    throw new Error('Invalid serialized data: too short');
+  }
+
+  const nonce = serialized.data.slice(0, NONCE_SIZE);
+  const ciphertext = serialized.data.slice(NONCE_SIZE);
+
+  return {
+    ciphertext,
+    nonce,
+    aad: serialized.aad,
+  };
+}
+
+/**
+ * Encrypts and serializes data in one step
+ */
+export function encryptAndSerialize(
+  plaintext: Uint8Array,
+  key: Uint8Array,
+  aad?: Uint8Array
+): SerializedEncryptedData {
+  const encrypted = encrypt(plaintext, key, aad);
+  return serialize(encrypted);
+}
+
+/**
+ * Deserializes and decrypts data in one step
+ */
+export function deserializeAndDecrypt(
+  serialized: SerializedEncryptedData,
+  key: Uint8Array
+): Uint8Array {
+  const encrypted = deserialize(serialized);
+  return decrypt(encrypted, key);
+}
+
+/**
+ * Converts encrypted data to hex string
+ */
+export function toHex(encryptedData: EncryptedData): string {
+  const serialized = serialize(encryptedData);
+  return bytesToHex(serialized.data);
+}
+
+/**
+ * Parses encrypted data from hex string
+ */
+export function fromHex(hex: string, aad?: Uint8Array): EncryptedData {
+  const normalized = hex.startsWith('0x') ? hex.slice(2) : hex;
+  const data = hexToBytes(normalized);
+
+  return deserialize({ data, aad });
+}
+
+/**
+ * Converts encrypted data to base64 string
+ */
+export function toBase64(encryptedData: EncryptedData): string {
+  const serialized = serialize(encryptedData);
+
+  if (typeof btoa === 'function') {
+    return btoa(String.fromCharCode(...serialized.data));
+  } else {
+    return Buffer.from(serialized.data).toString('base64');
+  }
+}
+
+/**
+ * Parses encrypted data from base64 string
+ */
+export function fromBase64(base64: string, aad?: Uint8Array): EncryptedData {
+  let data: Uint8Array;
+
+  if (typeof atob === 'function') {
+    const binary = atob(base64);
+    data = new Uint8Array(binary.length);
+    for (let i = 0; i < binary.length; i++) {
+      data[i] = binary.charCodeAt(i);
+    }
+  } else {
+    data = new Uint8Array(Buffer.from(base64, 'base64'));
+  }
+
+  return deserialize({ data, aad });
+}
+
+function validateKey(key: Uint8Array): void {
+  if (!(key instanceof Uint8Array)) {
+    throw new Error('Key must be a Uint8Array');
+  }
+
+  if (key.length !== KEY_SIZE) {
+    throw new Error(`Invalid key length: expected ${KEY_SIZE}, got ${key.length}`);
+  }
+}
+
+function validateNonce(nonce: Uint8Array): void {
+  if (!(nonce instanceof Uint8Array)) {
+    throw new Error('Nonce must be a Uint8Array');
+  }
+
+  if (nonce.length !== NONCE_SIZE) {
+    throw new Error(`Invalid nonce length: expected ${NONCE_SIZE}, got ${nonce.length}`);
+  }
+}
+
+/**
+ * Generates a random encryption key
+ */
+export function generateKey(): Uint8Array {
+  return randomBytes(KEY_SIZE);
+}
+
+/**
+ * Generates a random nonce
+ */
+export function generateNonce(): Uint8Array {
+  return randomBytes(NONCE_SIZE);
+}
+
+/**
+ * Securely clears a key from memory
+ */
+export function clearKey(key: Uint8Array): void {
+  key.fill(0);
+}
+
+/**
+ * Checks if encrypted data appears valid (basic structure check)
+ */
+export function isValidEncryptedData(data: EncryptedData): boolean {
+  return (
+    data.nonce instanceof Uint8Array &&
+    data.nonce.length === NONCE_SIZE &&
+    data.ciphertext instanceof Uint8Array &&
+    data.ciphertext.length >= TAG_SIZE
+  );
+}
diff --git a/src/vault/crypto/hkdf.ts b/src/vault/crypto/hkdf.ts
new file mode 100644
index 0000000..f2ba542
--- /dev/null
+++ b/src/vault/crypto/hkdf.ts
@@ -0,0 +1,42 @@
+/**
+ * HKDF Key Derivation
+ *
+ * Derives deterministic sub-keys from a master secret using HKDF-SHA256 (RFC 5869).
+ */
+
+import { hkdf } from '@noble/hashes/hkdf';
+import { sha256 } from '@noble/hashes/sha256';
+
+/** Default output length in bytes (256 bits) */
+const DEFAULT_KEY_LENGTH = 32;
+
+/** Maximum allowed output length (255 * SHA-256 output = 8160 bytes) */
+const MAX_KEY_LENGTH = 255 * 32;
+
+/**
+ * Derives a sub-key from input key material using HKDF-SHA256.
+ *
+ * @param ikm - Input key material (e.g., wallet private key). MUST be high-entropy.
+ * @param salt - Domain separation salt. Can be a string or bytes.
+ * @param info - Context-specific info. Can be a string or bytes.
+ * @param length - Output key length in bytes (default: 32).
+ * @returns Derived key as Uint8Array. Caller MUST zero this after use.
+ */
+export function deriveKeyHKDF(
+  ikm: Uint8Array,
+  salt: string | Uint8Array,
+  info: string | Uint8Array,
+  length: number = DEFAULT_KEY_LENGTH,
+): Uint8Array {
+  if (!ikm || ikm.length === 0) {
+    throw new Error('HKDF: input key material must not be empty');
+  }
+  if (length <= 0 || length > MAX_KEY_LENGTH) {
+    throw new Error(`HKDF: output length must be between 1 and ${MAX_KEY_LENGTH}`);
+  }
+
+  const saltBytes = typeof salt === 'string' ? new TextEncoder().encode(salt) : salt;
+  const infoBytes = typeof info === 'string' ? new TextEncoder().encode(info) : info;
+
+  return hkdf(sha256, ikm, saltBytes, infoBytes, length);
+}
diff --git a/src/vault/crypto/index.ts b/src/vault/crypto/index.ts
new file mode 100644
index 0000000..1ef3ceb
--- /dev/null
+++ b/src/vault/crypto/index.ts
@@ -0,0 +1,27 @@
+export {
+  encrypt,
+  decrypt,
+  encryptString,
+  decryptString,
+  serialize,
+  deserialize,
+  encryptAndSerialize,
+  deserializeAndDecrypt,
+  toHex,
+  fromHex,
+  toBase64,
+  fromBase64,
+  generateKey,
+  generateNonce,
+  clearKey,
+  isValidEncryptedData,
+  KEY_SIZE,
+  NONCE_SIZE,
+  TAG_SIZE,
+} from './aes';
+export type { EncryptedData, SerializedEncryptedData } from './aes';
+
+export { deriveKeyHKDF } from './hkdf';
+
+export { split as shamirSplit, combine as shamirCombine } from './shamir';
+export type { Share as ShamirShare } from './shamir';
diff --git a/src/vault/crypto/shamir.ts b/src/vault/crypto/shamir.ts
new file mode 100644
index 0000000..63a2c3a
--- /dev/null
+++ b/src/vault/crypto/shamir.ts
@@ -0,0 +1,173 @@
+/**
+ * Shamir's Secret Sharing over GF(2^8)
+ *
+ * Information-theoretic secret splitting: any K shares reconstruct the secret,
+ * K-1 shares reveal zero information.
+ *
+ * Uses GF(2^8) with irreducible polynomial x^8 + x^4 + x^3 + x + 1 (0x11B),
+ * same as AES. This is the standard choice for byte-level SSS.
+ */
+
+import { randomBytes } from '@noble/ciphers/webcrypto';
+
+// ── GF(2^8) Arithmetic ─────────────────────────────────────────────────────
+
+const IRREDUCIBLE = 0x11b;
+
+/** Exponential table: exp[log[a] + log[b]] = a * b */
+const EXP_TABLE = new Uint8Array(512);
+
+/** Logarithm table: log[a] for a in 1..255 (log[0] is undefined) */
+const LOG_TABLE = new Uint8Array(256);
+
+// Build log/exp tables using generator 3
+(function buildTables() {
+  let x = 1;
+  for (let i = 0; i < 255; i++) {
+    EXP_TABLE[i] = x;
+    LOG_TABLE[x] = i;
+    x = x ^ (x << 1); // multiply by generator (3 is primitive in this field)
+    if (x >= 256) x ^= IRREDUCIBLE;
+  }
+  // Extend exp table for easy modular arithmetic (avoid mod 255)
+  for (let i = 255; i < 512; i++) {
+    EXP_TABLE[i] = EXP_TABLE[i - 255]!;
+  }
+})();
+
+/** GF(2^8) addition: XOR */
+function gfAdd(a: number, b: number): number {
+  return a ^ b;
+}
+
+/** GF(2^8) multiplication via log/exp tables */
+function gfMul(a: number, b: number): number {
+  if (a === 0 || b === 0) return 0;
+  return EXP_TABLE[LOG_TABLE[a]! + LOG_TABLE[b]!]!;
+}
+
+/** GF(2^8) multiplicative inverse */
+function gfInv(a: number): number {
+  if (a === 0) throw new Error('GF(2^8): division by zero');
+  return EXP_TABLE[255 - LOG_TABLE[a]!]!;
+}
+
+/** GF(2^8) division: a / b */
+function gfDiv(a: number, b: number): number {
+  if (b === 0) throw new Error('GF(2^8): division by zero');
+  if (a === 0) return 0;
+  return EXP_TABLE[(LOG_TABLE[a]! - LOG_TABLE[b]! + 255) % 255]!;
+}
+
+// ── Share Type ──────────────────────────────────────────────────────────────
+
+/** A single Shamir share */
+export interface Share {
+  /** Share index (1..N, never 0) */
+  x: number;
+  /** Share data (same length as secret) */
+  y: Uint8Array;
+}
+
+// ── Split ───────────────────────────────────────────────────────────────────
+
+/**
+ * Splits a secret into N shares with threshold K.
+ *
+ * @param secret - Secret bytes to split (any length)
+ * @param n - Total number of shares to create (2..255)
+ * @param k - Minimum shares needed for reconstruction (2..n)
+ * @returns Array of N shares
+ */
+export function split(secret: Uint8Array, n: number, k: number): Share[] {
+  if (k < 2) throw new Error('Threshold K must be at least 2');
+  if (n < k) throw new Error('Share count N must be >= threshold K');
+  if (n > 255) throw new Error('Maximum 255 shares (GF(2^8) limit)');
+  if (secret.length === 0) throw new Error('Secret must not be empty');
+
+  const coefficients = new Array<Uint8Array>(secret.length);
+  for (let i = 0; i < secret.length; i++) {
+    const poly = new Uint8Array(k);
+    poly[0] = secret[i]!;
+    const rand = randomBytes(k - 1);
+    poly.set(rand, 1);
+    coefficients[i] = poly;
+  }
+
+  const shares: Share[] = [];
+  for (let xi = 1; xi <= n; xi++) {
+    const y = new Uint8Array(secret.length);
+    for (let byteIdx = 0; byteIdx < secret.length; byteIdx++) {
+      y[byteIdx] = evaluatePolynomial(coefficients[byteIdx]!, xi);
+    }
+    shares.push({ x: xi, y });
+  }
+
+  for (const poly of coefficients) {
+    poly.fill(0);
+  }
+
+  return shares;
+}
+
+function evaluatePolynomial(coeffs: Uint8Array, x: number): number {
+  let result = 0;
+  for (let i = coeffs.length - 1; i >= 0; i--) {
+    result = gfAdd(gfMul(result, x), coeffs[i]!);
+  }
+  return result;
+}
+
+// ── Combine ─────────────────────────────────────────────────────────────────
+
+/**
+ * Reconstructs a secret from K or more shares using Lagrange interpolation.
+ *
+ * @param shares - Array of K or more shares (must all have same y.length)
+ * @returns Reconstructed secret
+ */
+export function combine(shares: Share[]): Uint8Array {
+  if (shares.length < 2) throw new Error('Need at least 2 shares');
+
+  const secretLength = shares[0]!.y.length;
+  for (const share of shares) {
+    if (share.y.length !== secretLength) {
+      throw new Error('All shares must have the same data length');
+    }
+    if (share.x === 0) {
+      throw new Error('Share index must not be 0');
+    }
+  }
+
+  const xValues = new Set(shares.map(s => s.x));
+  if (xValues.size !== shares.length) {
+    throw new Error('Duplicate share indices');
+  }
+
+  const secret = new Uint8Array(secretLength);
+
+  for (let byteIdx = 0; byteIdx < secretLength; byteIdx++) {
+    let value = 0;
+
+    for (let i = 0; i < shares.length; i++) {
+      const xi = shares[i]!.x;
+      const yi = shares[i]!.y[byteIdx]!;
+
+      let basis = 1;
+      for (let j = 0; j < shares.length; j++) {
+        if (i === j) continue;
+        const xj = shares[j]!.x;
+        basis = gfMul(basis, gfDiv(xj, gfAdd(xi, xj)));
+      }
+
+      value = gfAdd(value, gfMul(yi, basis));
+    }
+
+    secret[byteIdx] = value;
+  }
+
+  return secret;
+}
+
+/** @internal Exported for cross-platform test vector validation */
+export const _gf = { add: gfAdd, mul: gfMul, inv: gfInv, div: gfDiv, EXP_TABLE, LOG_TABLE } as const;
diff --git a/src/vault/index.ts b/src/vault/index.ts
new file mode 100644
index 0000000..b0eecdc
--- /dev/null
+++ b/src/vault/index.ts
@@ -0,0 +1,65 @@
+// High-level vault client
+export { VaultClient } from './client';
+export { adaptiveThreshold, writeQuorum } from './quorum';
+export type {
+  VaultConfig,
+  SecretMeta,
+  StoreResult,
+  RetrieveResult,
+  ListResult,
+  DeleteResult,
+  GuardianResult,
+} from './types';
+
+// Vault auth (renamed to avoid collision with top-level AuthClient)
+export { AuthClient as VaultAuthClient } from './auth';
+
+// Transport (guardian communication)
+export { GuardianClient, GuardianError } from './transport';
+export { fanOut, fanOutIndexed, withTimeout, withRetry } from './transport';
+export type {
+  GuardianEndpoint,
+  GuardianErrorCode,
+  GuardianInfo,
+  HealthResponse as GuardianHealthResponse,
+  StatusResponse as GuardianStatusResponse,
+  PushResponse,
+  PullResponse,
+  StoreSecretResponse,
+  GetSecretResponse,
+  DeleteSecretResponse,
+  ListSecretsResponse,
+  SecretEntry,
+  ChallengeResponse as GuardianChallengeResponse,
+  SessionResponse as GuardianSessionResponse,
+  FanOutResult,
+} from './transport';
+
+// Crypto primitives
+export {
+  encrypt,
+  decrypt,
+  encryptString,
+  decryptString,
+  serialize as serializeEncrypted,
+  deserialize as deserializeEncrypted,
+  encryptAndSerialize,
+  deserializeAndDecrypt,
+  toHex as encryptedToHex,
+  fromHex as encryptedFromHex,
+  toBase64 as encryptedToBase64,
+  fromBase64 as encryptedFromBase64,
+  generateKey,
+  generateNonce,
+  clearKey,
+  isValidEncryptedData,
+  KEY_SIZE,
+  NONCE_SIZE,
+  TAG_SIZE,
+} from './crypto';
+export type { EncryptedData, SerializedEncryptedData } from './crypto';
+
+export { deriveKeyHKDF } from './crypto';
+
+export { shamirSplit, shamirCombine } from './crypto';
+export type { ShamirShare } from './crypto';
diff --git a/src/vault/quorum.ts b/src/vault/quorum.ts
new file mode 100644
index 0000000..f621c33
--- /dev/null
+++ b/src/vault/quorum.ts
@@ -0,0 +1,16 @@
+/**
+ * Quorum calculations for distributed vault operations.
+ * Must match orama-vault (Zig side).
+ */
+
+/** Adaptive Shamir threshold: max(3, floor(N/3)). */
+export function adaptiveThreshold(n: number): number {
+  return Math.max(3, Math.floor(n / 3));
+}
+
+/** Write quorum: ceil(2N/3). Requires majority for consistency. */
+export function writeQuorum(n: number): number {
+  if (n === 0) return 0;
+  if (n <= 2) return n;
+  return Math.ceil((2 * n) / 3);
+}
diff --git a/src/vault/transport/fanout.ts b/src/vault/transport/fanout.ts
new file mode 100644
index 0000000..fce3786
--- /dev/null
+++ b/src/vault/transport/fanout.ts
@@ -0,0 +1,94 @@
+import { GuardianClient, GuardianError } from './guardian';
+import type { GuardianEndpoint, GuardianErrorCode, FanOutResult } from './types';
+
+/**
+ * Fan out an operation to multiple guardians in parallel.
+ * Returns results from all guardians (both successes and failures).
+ */
+export async function fanOut<T>(
+  guardians: GuardianEndpoint[],
+  operation: (client: GuardianClient) => Promise<T>,
+): Promise<FanOutResult<T>[]> {
+  const results = await Promise.allSettled(
+    guardians.map(async (endpoint) => {
+      const client = new GuardianClient(endpoint);
+      const result = await operation(client);
+      return { endpoint, result, error: null } as FanOutResult<T>;
+    }),
+  );
+
+  return results.map((r, i) => {
+    if (r.status === 'fulfilled') return r.value;
+    const reason = r.reason as Error;
+    const errorCode: GuardianErrorCode | undefined = reason instanceof GuardianError ? reason.code : undefined;
+    return {
+      endpoint: guardians[i]!,
+      result: null,
+      error: reason.message,
+      errorCode,
+    };
+  });
+}
+
+/**
+ * Fan out an indexed operation to multiple guardians in parallel.
+ * The operation receives the index so each guardian can get a different share.
+ */
+export async function fanOutIndexed<T>(
+  guardians: GuardianEndpoint[],
+  operation: (client: GuardianClient, index: number) => Promise<T>,
+): Promise<FanOutResult<T>[]> {
+  const results = await Promise.allSettled(
+    guardians.map(async (endpoint, i) => {
+      const client = new GuardianClient(endpoint);
+      const result = await operation(client, i);
+      return { endpoint, result, error: null } as FanOutResult<T>;
+    }),
+  );
+
+  return results.map((r, i) => {
+    if (r.status === 'fulfilled') return r.value;
+    const reason = r.reason as Error;
+    const errorCode: GuardianErrorCode | undefined = reason instanceof GuardianError ? reason.code : undefined;
+    return {
+      endpoint: guardians[i]!,
+      result: null,
+      error: reason.message,
+      errorCode,
+    };
+  });
+}
+
+/**
+ * Race a promise against a timeout.
+ */
+export function withTimeout<T>(promise: Promise<T>, ms: number): Promise<T> {
+  return Promise.race([
+    promise,
+    new Promise<never>((_, reject) =>
+      setTimeout(() => reject(new Error(`timeout after ${ms}ms`)), ms),
+    ),
+  ]);
+}
+
+/**
+ * Retry a function with exponential backoff.
+ * Does not retry auth or not-found errors.
+ */
+export async function withRetry<T>(fn: () => Promise<T>, attempts = 3): Promise<T> {
+  let lastError: Error | undefined;
+  for (let i = 0; i < attempts; i++) {
+    try {
+      return await fn();
+    } catch (err) {
+      lastError = err as Error;
+      if (err instanceof GuardianError && (err.code === 'AUTH' || err.code === 'NOT_FOUND')) {
+        throw err;
+      }
+      if (i < attempts - 1) {
+        await new Promise((r) => setTimeout(r, 200 * Math.pow(2, i)));
+      }
+    }
+  }
+  throw lastError!;
+}
diff --git a/src/vault/transport/guardian.ts b/src/vault/transport/guardian.ts
new file mode 100644
index 0000000..66b06e7
--- /dev/null
+++ b/src/vault/transport/guardian.ts
@@ -0,0 +1,285 @@
+import type {
+  GuardianEndpoint,
+  GuardianErrorCode,
+  GuardianErrorBody,
+  HealthResponse,
+  StatusResponse,
+  GuardianInfo,
+  PushResponse,
+  PullResponse,
+  StoreSecretResponse,
+  GetSecretResponse,
+  DeleteSecretResponse,
+  ListSecretsResponse,
+  ChallengeResponse,
+  SessionResponse,
+} from './types';
+
+export class GuardianError extends Error {
+  constructor(public readonly code: GuardianErrorCode, message: string) {
+    super(message);
+    this.name = 'GuardianError';
+  }
+}
+
+const DEFAULT_TIMEOUT_MS = 10_000;
+
+/**
+ * HTTP client for a single orama-vault guardian node.
+ * Supports V1 (push/pull) and V2 (CRUD secrets) endpoints.
+ */
+export class GuardianClient {
+  private baseUrl: string;
+  private timeoutMs: number;
+  private sessionToken: string | null = null;
+
+  constructor(endpoint: GuardianEndpoint, timeoutMs = DEFAULT_TIMEOUT_MS) {
+    this.baseUrl = `http://${endpoint.address}:${endpoint.port}`;
+    this.timeoutMs = timeoutMs;
+  }
+
+  /** Set a session token for authenticated V2 requests. */
+  setSessionToken(token: string): void {
+    this.sessionToken = token;
+  }
+
+  /** Get the current session token. */
+  getSessionToken(): string | null {
+    return this.sessionToken;
+  }
+
+  /** Clear the session token. */
+  clearSessionToken(): void {
+    this.sessionToken = null;
+  }
+
+  // ── V1 endpoints ────────────────────────────────────────────────────
+
+  /** GET /v1/vault/health */
+  async health(): Promise<HealthResponse> {
+    return this.get<HealthResponse>('/v1/vault/health');
+  }
+
+  /** GET /v1/vault/status */
+  async status(): Promise<StatusResponse> {
+    return this.get<StatusResponse>('/v1/vault/status');
+  }
+
+  /** GET /v1/vault/guardians */
+  async guardians(): Promise<GuardianInfo> {
+    return this.get<GuardianInfo>('/v1/vault/guardians');
+  }
+
+  /** POST /v1/vault/push — store a share (V1). */
+  async push(identity: string, share: Uint8Array): Promise<PushResponse> {
+    return this.post<PushResponse>('/v1/vault/push', {
+      identity,
+      share: uint8ToBase64(share),
+    });
+  }
+
+  /** POST /v1/vault/pull — retrieve a share (V1). */
+  async pull(identity: string): Promise<Uint8Array> {
+    const resp = await this.post<PullResponse>('/v1/vault/pull', { identity });
+    return base64ToUint8(resp.share);
+  }
+
+  /** Check if this guardian is reachable. */
+  async isReachable(): Promise<boolean> {
+    try {
+      await this.health();
+      return true;
+    } catch {
+      return false;
+    }
+  }
+
+  // ── V2 auth endpoints ───────────────────────────────────────────────
+
+  /** POST /v2/vault/auth/challenge — request an auth challenge. */
+  async requestChallenge(identity: string): Promise<ChallengeResponse> {
+    return this.post<ChallengeResponse>('/v2/vault/auth/challenge', { identity });
+  }
+
+  /** POST /v2/vault/auth/session — exchange challenge for session token. */
+  async createSession(identity: string, nonce: string, created_ns: number, tag: string): Promise<SessionResponse> {
+    return this.post<SessionResponse>('/v2/vault/auth/session', {
+      identity,
+      nonce,
+      created_ns,
+      tag,
+    });
+  }
+
+  // ── V2 secrets CRUD ─────────────────────────────────────────────────
+
+  /** PUT /v2/vault/secrets/{name} — store a secret. Requires session token. */
+  async putSecret(name: string, share: Uint8Array, version: number): Promise<StoreSecretResponse> {
+    return this.authedRequest<StoreSecretResponse>('PUT', `/v2/vault/secrets/${encodeURIComponent(name)}`, {
+      share: uint8ToBase64(share),
+      version,
+    });
+  }
+
+  /** GET /v2/vault/secrets/{name} — retrieve a secret. Requires session token. */
+  async getSecret(name: string): Promise<{ share: Uint8Array; name: string; version: number; created_ns: number; updated_ns: number }> {
+    const resp = await this.authedRequest<GetSecretResponse>('GET', `/v2/vault/secrets/${encodeURIComponent(name)}`);
+    return {
+      share: base64ToUint8(resp.share),
+      name: resp.name,
+      version: resp.version,
+      created_ns: resp.created_ns,
+      updated_ns: resp.updated_ns,
+    };
+  }
+
+  /** DELETE /v2/vault/secrets/{name} — delete a secret. Requires session token. */
+  async deleteSecret(name: string): Promise<DeleteSecretResponse> {
+    return this.authedRequest<DeleteSecretResponse>('DELETE', `/v2/vault/secrets/${encodeURIComponent(name)}`);
+  }
+
+  /** GET /v2/vault/secrets — list all secrets. Requires session token. */
+  async listSecrets(): Promise<ListSecretsResponse> {
+    return this.authedRequest<ListSecretsResponse>('GET', '/v2/vault/secrets');
+  }
+
+  // ── Internal HTTP methods ───────────────────────────────────────────
+
+  private async authedRequest<T>(method: string, path: string, body?: unknown): Promise<T> {
+    if (!this.sessionToken) {
+      throw new GuardianError('AUTH', 'No session token set. Call authenticate() first.');
+    }
+
+    const controller = new AbortController();
+    const timeout = setTimeout(() => controller.abort(), this.timeoutMs);
+
+    try {
+      const headers: Record<string, string> = {
+        'X-Session-Token': this.sessionToken,
+      };
+      const init: RequestInit = {
+        method,
+        headers,
+        signal: controller.signal,
+      };
+
+      if (body !== undefined) {
+        headers['Content-Type'] = 'application/json';
+        init.body = JSON.stringify(body);
+      }
+
+      const resp = await fetch(`${this.baseUrl}${path}`, init);
+
+      if (!resp.ok) {
+        const errBody = (await resp.json().catch(() => ({}))) as GuardianErrorBody;
+        const msg = errBody.error || `HTTP ${resp.status}`;
+        throw new GuardianError(classifyHttpStatus(resp.status), msg);
+      }
+
+      return (await resp.json()) as T;
+    } catch (err) {
+      throw classifyError(err);
+    } finally {
+      clearTimeout(timeout);
+    }
+  }
+
+  private async get<T>(path: string): Promise<T> {
+    const controller = new AbortController();
+    const timeout = setTimeout(() => controller.abort(), this.timeoutMs);
+
+    try {
+      const resp = await fetch(`${this.baseUrl}${path}`, {
+        method: 'GET',
+        signal: controller.signal,
+      });
+
+      if (!resp.ok) {
+        const body = (await resp.json().catch(() => ({}))) as GuardianErrorBody;
+        const msg = body.error || `HTTP ${resp.status}`;
+        throw new GuardianError(classifyHttpStatus(resp.status), msg);
+      }
+
+      return (await resp.json()) as T;
+    } catch (err) {
+      throw classifyError(err);
+    } finally {
+      clearTimeout(timeout);
+    }
+  }
+
+  private async post<T>(path: string, body: unknown): Promise<T> {
+    const controller = new AbortController();
+    const timeout = setTimeout(() => controller.abort(), this.timeoutMs);
+
+    try {
+      const resp = await fetch(`${this.baseUrl}${path}`, {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify(body),
+        signal: controller.signal,
+      });
+
+      if (!resp.ok) {
+        const errBody = (await resp.json().catch(() => ({}))) as GuardianErrorBody;
+        const msg = errBody.error || `HTTP ${resp.status}`;
+        throw new GuardianError(classifyHttpStatus(resp.status), msg);
+      }
+
+      return (await resp.json()) as T;
+    } catch (err) {
+      throw classifyError(err);
+    } finally {
+      clearTimeout(timeout);
+    }
+  }
+}
+
+// ── Error classification ──────────────────────────────────────────────────
+
+function classifyHttpStatus(status: number): GuardianErrorCode {
+  if (status === 404) return 'NOT_FOUND';
+  if (status === 401 || status === 403) return 'AUTH';
+  if (status === 409) return 'CONFLICT';
+  if (status >= 500) return 'SERVER_ERROR';
+  return 'NETWORK';
+}
+
+function classifyError(err: unknown): GuardianError {
+  if (err instanceof GuardianError) return err;
+  if (err instanceof Error) {
+    if (err.name === 'AbortError') {
+      return new GuardianError('TIMEOUT', `Request timed out: ${err.message}`);
+    }
+    if (err.name === 'TypeError' || err.message.includes('fetch')) {
+      return new GuardianError('NETWORK', `Network error: ${err.message}`);
+    }
+    return new GuardianError('NETWORK', err.message);
+  }
+  return new GuardianError('NETWORK', String(err));
+}
+
+// ── Base64 helpers ────────────────────────────────────────────────────────
+
+function uint8ToBase64(bytes: Uint8Array): string {
+  if (typeof Buffer !== 'undefined') {
+    return Buffer.from(bytes).toString('base64');
+  }
+  let binary = '';
+  for (let i = 0; i < bytes.length; i++) {
+    binary += String.fromCharCode(bytes[i]!);
+  }
+  return btoa(binary);
+}
+
+function base64ToUint8(b64: string): Uint8Array {
+  if (typeof Buffer !== 'undefined') {
+    return new Uint8Array(Buffer.from(b64, 'base64'));
+  }
+  const binary = atob(b64);
+  const bytes = new Uint8Array(binary.length);
+  for (let i = 0; i < binary.length; i++) {
+    bytes[i] = binary.charCodeAt(i);
+  }
+  return bytes;
+}
diff --git a/src/vault/transport/index.ts b/src/vault/transport/index.ts
new file mode 100644
index 0000000..ebdcfeb
--- /dev/null
+++ b/src/vault/transport/index.ts
@@ -0,0 +1,19 @@
+export { GuardianClient, GuardianError } from './guardian';
+export { fanOut, fanOutIndexed, withTimeout, withRetry } from './fanout';
+export type {
+  GuardianEndpoint,
+  GuardianErrorCode,
+  GuardianInfo,
+  HealthResponse,
+  StatusResponse,
+  PushResponse,
+  PullResponse,
+  StoreSecretResponse,
+  GetSecretResponse,
+  DeleteSecretResponse,
+  ListSecretsResponse,
+  SecretEntry,
+  ChallengeResponse,
+  SessionResponse,
+  FanOutResult,
+} from './types';
diff --git a/src/vault/transport/types.ts b/src/vault/transport/types.ts
new file mode 100644
index 0000000..cb740b5
--- /dev/null
+++ b/src/vault/transport/types.ts
@@ -0,0 +1,101 @@
+/** A guardian node endpoint. */
+export interface GuardianEndpoint {
+  address: string;
+  port: number;
+}
+
+/** V1 push response. */
+export interface PushResponse {
+  status: string;
+}
+
+/** V1 pull response. */
+export interface PullResponse {
+  share: string; // base64
+}
+
+/** V2 store response. */
+export interface StoreSecretResponse {
+  status: string;
+  name: string;
+  version: number;
+}
+
+/** V2 get response. */
+export interface GetSecretResponse {
+  share: string; // base64
+  name: string;
+  version: number;
+  created_ns: number;
+  updated_ns: number;
+}
+
+/** V2 delete response. */
+export interface DeleteSecretResponse {
+  status: string;
+  name: string;
+}
+
+/** V2 list response. */
+export interface ListSecretsResponse {
+  secrets: SecretEntry[];
+}
+
+/** An entry in the list secrets response. */
+export interface SecretEntry {
+  name: string;
+  version: number;
+  size: number;
+}
+
+/** Health check response. */
+export interface HealthResponse {
+  status: string;
+  version: string;
+}
+
+/** Status response. */
+export interface StatusResponse {
+  status: string;
+  version: string;
+  data_dir: string;
+  client_port: number;
+  peer_port: number;
+}
+
+/** Guardian info response. */
+export interface GuardianInfo {
+  guardians: Array<{ address: string; port: number }>;
+  threshold: number;
+  total: number;
+}
+
+/** Challenge response from auth endpoint. */
+export interface ChallengeResponse {
+  nonce: string;
+  created_ns: number;
+  tag: string;
+}
+
+/** Session token response from auth endpoint. */
+export interface SessionResponse {
+  identity: string;
+  expiry_ns: number;
+  tag: string;
+}
+
+/** Error body from guardian. */
+export interface GuardianErrorBody {
+  error: string;
+}
+
+/** Error classification codes. */
+export type GuardianErrorCode = 'TIMEOUT' | 'NOT_FOUND' | 'AUTH' | 'SERVER_ERROR' | 'NETWORK' | 'CONFLICT';
+
+/** Fan-out result for a single guardian. */
+export interface FanOutResult<T> {
+  endpoint: GuardianEndpoint;
+  result: T | null;
+  error: string | null;
+  errorCode?: GuardianErrorCode;
+}
diff --git a/src/vault/types.ts b/src/vault/types.ts
new file mode 100644
index 0000000..febb30d
--- /dev/null
+++ b/src/vault/types.ts
@@ -0,0 +1,62 @@
+import type { GuardianEndpoint } from './transport/types';
+
+/** Configuration for VaultClient. */
+export interface VaultConfig {
+  /** Guardian endpoints to connect to. */
+  guardians: GuardianEndpoint[];
+  /** HMAC key for authentication (derived from user's secret). */
+  hmacKey: Uint8Array;
+  /** Identity hash (hex string, 64 chars). */
+  identityHex: string;
+  /** Request timeout in ms (default: 10000). */
+  timeoutMs?: number;
+}
+
+/** Metadata for a stored secret. */
+export interface SecretMeta {
+  name: string;
+  version: number;
+  size: number;
+}
+
+/** Result of a store operation. */
+export interface StoreResult {
+  /** Number of guardians that acknowledged. */
+  ackCount: number;
+  /** Total guardians contacted. */
+  totalContacted: number;
+  /** Number of failures. */
+  failCount: number;
+  /** Whether write quorum was met. */
+  quorumMet: boolean;
+  /** Per-guardian results. */
+  guardianResults: GuardianResult[];
+}
+
+/** Result of a retrieve operation. */
+export interface RetrieveResult {
+  /** The reconstructed secret data. */
+  data: Uint8Array;
+  /** Number of shares collected. */
+  sharesCollected: number;
+}
+
+/** Result of a list operation. */
+export interface ListResult {
+  secrets: SecretMeta[];
+}
+
+/** Result of a delete operation. */
+export interface DeleteResult {
+  /** Number of guardians that acknowledged. */
+  ackCount: number;
+  totalContacted: number;
+  quorumMet: boolean;
+}
+
+/** Per-guardian operation result. */
+export interface GuardianResult {
+  endpoint: string;
+  success: boolean;
+  error?: string;
+}
diff --git a/tests/unit/vault-auth/auth.test.ts b/tests/unit/vault-auth/auth.test.ts
new file mode 100644
index 0000000..0b3f1dc
--- /dev/null
+++ b/tests/unit/vault-auth/auth.test.ts
@@ -0,0 +1,20 @@
+import { describe, it, expect } from 'vitest';
+import { AuthClient } from '../../../src/vault/auth';
+
+describe('AuthClient', () => {
+  it('constructs with identity', () => {
+    const auth = new AuthClient('a'.repeat(64));
+    expect(auth.getIdentityHex()).toBe('a'.repeat(64));
+  });
+
+  it('clearSessions does not throw', () => {
+    const auth = new AuthClient('b'.repeat(64));
+    expect(() => auth.clearSessions()).not.toThrow();
+  });
+
+  it('authenticateAll returns empty for no endpoints', async () => {
+    const auth = new AuthClient('c'.repeat(64));
+    const results = await auth.authenticateAll([]);
+    expect(results).toEqual([]);
+  });
+});
diff --git a/tests/unit/vault-crypto/aes.test.ts b/tests/unit/vault-crypto/aes.test.ts
new file mode 100644
index 0000000..0757a0a
--- /dev/null
+++ b/tests/unit/vault-crypto/aes.test.ts
@@ -0,0 +1,99 @@
+import { describe, it, expect } from 'vitest';
+import {
+  encrypt,
+  decrypt,
+  encryptString,
+  decryptString,
+  generateKey,
+  clearKey,
+  serialize,
+  deserialize,
+  toHex,
+  fromHex,
+  toBase64,
+  fromBase64,
+  isValidEncryptedData,
+  KEY_SIZE,
+  NONCE_SIZE,
+} from '../../../src/vault/crypto/aes';
+
+describe('AES-256-GCM', () => {
+  it('encrypt/decrypt round-trip', () => {
+    const key = generateKey();
+    const plaintext = new TextEncoder().encode('hello vault');
+    const encrypted = encrypt(plaintext, key);
+    const decrypted = decrypt(encrypted, key);
+    expect(decrypted).toEqual(plaintext);
+    clearKey(key);
+  });
+
+  it('encryptString/decryptString round-trip', () => {
+    const key = generateKey();
+    const msg = 'sensitive data 123';
+    const encrypted = encryptString(msg, key);
+    const decrypted = decryptString(encrypted, key);
+    expect(decrypted).toBe(msg);
+    clearKey(key);
+  });
+
+  it('different keys cannot decrypt', () => {
+    const key1 = generateKey();
+    const key2 = generateKey();
+    const encrypted = encrypt(new Uint8Array([1, 2, 3]), key1);
+    expect(() => decrypt(encrypted, key2)).toThrow();
+    clearKey(key1);
+    clearKey(key2);
+  });
+
+  it('nonce is correct size', () => {
+    const key = generateKey();
+    const encrypted = encrypt(new Uint8Array([42]), key);
+    expect(encrypted.nonce.length).toBe(NONCE_SIZE);
+    clearKey(key);
+  });
+
+  it('rejects invalid key size', () => {
+    expect(() => encrypt(new Uint8Array([1]), new Uint8Array(16))).toThrow('Invalid key length');
+  });
+
+  it('serialize/deserialize round-trip', () => {
+    const key = generateKey();
+    const encrypted = encrypt(new Uint8Array([1, 2, 3]), key);
+    const serialized = serialize(encrypted);
+    const deserialized = deserialize(serialized);
+    expect(decrypt(deserialized, key)).toEqual(new Uint8Array([1, 2, 3]));
+    clearKey(key);
+  });
+
+  it('toHex/fromHex round-trip', () => {
+    const key = generateKey();
+    const encrypted = encrypt(new Uint8Array([10, 20, 30]), key);
+    const hex = toHex(encrypted);
+    const restored = fromHex(hex);
+    expect(decrypt(restored, key)).toEqual(new Uint8Array([10, 20, 30]));
+    clearKey(key);
+  });
+
+  it('toBase64/fromBase64 round-trip', () => {
+    const key = generateKey();
+    const encrypted = encrypt(new Uint8Array([99]), key);
+    const b64 = toBase64(encrypted);
+    const restored = fromBase64(b64);
+    expect(decrypt(restored, key)).toEqual(new Uint8Array([99]));
+    clearKey(key);
+  });
+
+  it('isValidEncryptedData checks structure', () => {
+    const key = generateKey();
+    const encrypted = encrypt(new Uint8Array([1]), key);
+    expect(isValidEncryptedData(encrypted)).toBe(true);
+    expect(isValidEncryptedData({ ciphertext: new Uint8Array(0), nonce: new Uint8Array(0) })).toBe(false);
+    clearKey(key);
+  });
+
+  it('generateKey produces KEY_SIZE bytes', () => {
+    const key = generateKey();
+    expect(key.length).toBe(KEY_SIZE);
+    clearKey(key);
+  });
+});
diff --git a/tests/unit/vault-crypto/hkdf.test.ts b/tests/unit/vault-crypto/hkdf.test.ts
new file mode 100644
index 0000000..f242f59
--- /dev/null
+++ b/tests/unit/vault-crypto/hkdf.test.ts
@@ -0,0 +1,49 @@
+import { describe, it, expect } from 'vitest';
+import { deriveKeyHKDF } from '../../../src/vault/crypto/hkdf';
+
+describe('HKDF Derivation', () => {
+  it('derives 32-byte key by default', () => {
+    const ikm = new Uint8Array(32).fill(0xab);
+    const key = deriveKeyHKDF(ikm, 'test-salt', 'test-info');
+    expect(key.length).toBe(32);
+  });
+
+  it('same inputs produce same output', () => {
+    const ikm = new Uint8Array(32).fill(0x42);
+    const key1 = deriveKeyHKDF(ikm, 'salt', 'info');
+    const key2 = deriveKeyHKDF(ikm, 'salt', 'info');
+    expect(key1).toEqual(key2);
+  });
+
+  it('different salts produce different keys', () => {
+    const ikm = new Uint8Array(32).fill(0x42);
+    const key1 = deriveKeyHKDF(ikm, 'salt-a', 'info');
+    const key2 = deriveKeyHKDF(ikm, 'salt-b', 'info');
+    expect(key1).not.toEqual(key2);
+  });
+
+  it('different info produce different keys', () => {
+    const ikm = new Uint8Array(32).fill(0x42);
+    const key1 = deriveKeyHKDF(ikm, 'salt', 'info-a');
+    const key2 = deriveKeyHKDF(ikm, 'salt', 'info-b');
+    expect(key1).not.toEqual(key2);
+  });
+
+  it('custom length', () => {
+    const ikm = new Uint8Array(32).fill(0x42);
+    const key = deriveKeyHKDF(ikm, 'salt', 'info', 64);
+    expect(key.length).toBe(64);
+  });
+
+  it('throws on empty ikm', () => {
+    expect(() => deriveKeyHKDF(new Uint8Array(0), 'salt', 'info')).toThrow('must not be empty');
+  });
+
+  it('accepts Uint8Array salt and info', () => {
+    const ikm = new Uint8Array(32).fill(0xab);
+    const salt = new Uint8Array([1, 2, 3]);
+    const info = new Uint8Array([4, 5, 6]);
+    const key = deriveKeyHKDF(ikm, salt, info);
+    expect(key.length).toBe(32);
+  });
+});
diff --git a/tests/unit/vault-crypto/shamir.test.ts b/tests/unit/vault-crypto/shamir.test.ts
new file mode 100644
index 0000000..d5941ad
--- /dev/null
+++ b/tests/unit/vault-crypto/shamir.test.ts
@@ -0,0 +1,80 @@
+import { describe, it, expect } from 'vitest';
+import { split, combine } from '../../../src/vault/crypto/shamir';
+
+describe('Shamir SSS', () => {
+  it('2-of-3 round-trip', () => {
+    const secret = new Uint8Array([42]);
+    const shares = split(secret, 3, 2);
+    expect(shares).toHaveLength(3);
+
+    const recovered = combine([shares[0]!, shares[1]!]);
+    expect(recovered).toEqual(secret);
+
+    const recovered2 = combine([shares[0]!, shares[2]!]);
+    expect(recovered2).toEqual(secret);
+  });
+
+  it('3-of-5 multi-byte', () => {
+    const secret = new Uint8Array([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);
+    const shares = split(secret, 5, 3);
+    expect(shares).toHaveLength(5);
+    const recovered = combine([shares[0]!, shares[2]!, shares[4]!]);
+    expect(recovered).toEqual(secret);
+  });
+
+  it('all C(5,3) subsets reconstruct', () => {
+    const secret = new Uint8Array([42, 137, 255, 0]);
+    const shares = split(secret, 5, 3);
+    for (let i = 0; i < 5; i++) {
+      for (let j = i + 1; j < 5; j++) {
+        for (let l = j + 1; l < 5; l++) {
+          const recovered = combine([shares[i]!, shares[j]!, shares[l]!]);
+          expect(recovered).toEqual(secret);
+        }
+      }
+    }
+  });
+
+  it('share indices are 1..N', () => {
+    const shares = split(new Uint8Array([42]), 5, 3);
+    expect(shares.map(s => s.x)).toEqual([1, 2, 3, 4, 5]);
+  });
+
+  it('throws on K < 2', () => {
+    expect(() => split(new Uint8Array([1]), 3, 1)).toThrow('Threshold K must be at least 2');
+  });
+
+  it('throws on N < K', () => {
+    expect(() => split(new Uint8Array([1]), 2, 3)).toThrow('Share count N must be >= threshold K');
+  });
+
+  it('throws on N > 255', () => {
+    expect(() => split(new Uint8Array([1]), 256, 2)).toThrow('Maximum 255 shares');
+  });
+
+  it('throws on empty secret', () => {
+    expect(() => split(new Uint8Array(0), 3, 2)).toThrow('Secret must not be empty');
+  });
+
+  it('throws on duplicate shares', () => {
+    expect(() => combine([
+      { x: 1, y: new Uint8Array([1]) },
+      { x: 1, y: new Uint8Array([2]) },
+    ])).toThrow('Duplicate share indices');
+  });
+
+  it('throws on mismatched lengths', () => {
+    expect(() => combine([
+      { x: 1, y: new Uint8Array([1, 2]) },
+      { x: 2, y: new Uint8Array([3]) },
+    ])).toThrow('same data length');
+  });
+
+  it('large secret (256 bytes)', () => {
+    const secret = new Uint8Array(256);
+    for (let i = 0; i < 256; i++) secret[i] = i;
+    const shares = split(secret, 10, 5);
+    const recovered = combine(shares.slice(0, 5));
+    expect(recovered).toEqual(secret);
+  });
+});
diff --git a/tests/unit/vault-transport/fanout.test.ts b/tests/unit/vault-transport/fanout.test.ts
new file mode 100644
index 0000000..852b9ae
--- /dev/null
+++ b/tests/unit/vault-transport/fanout.test.ts
@@ -0,0 +1,19 @@
+import { describe, it, expect } from 'vitest';
+import { withTimeout } from '../../../src/vault/transport/fanout';
+
+describe('withTimeout', () => {
+  it('resolves when promise completes before timeout', async () => {
+    const result = await withTimeout(Promise.resolve('ok'), 1000);
+    expect(result).toBe('ok');
+  });
+
+  it('rejects when timeout expires', async () => {
+    const slow = new Promise<string>((resolve) => setTimeout(() => resolve('late'), 500));
+    await expect(withTimeout(slow, 50)).rejects.toThrow('timeout after 50ms');
+  });
+
+  it('propagates original error', async () => {
+    const failing = Promise.reject(new Error('original'));
+    await expect(withTimeout(failing, 1000)).rejects.toThrow('original');
+  });
+});
diff --git a/tests/unit/vault-transport/guardian.test.ts b/tests/unit/vault-transport/guardian.test.ts
new file mode 100644
index 0000000..879e41b
--- /dev/null
+++ b/tests/unit/vault-transport/guardian.test.ts
@@ -0,0 +1,48 @@
+import { describe, it, expect } from 'vitest';
+import { GuardianClient, GuardianError } from '../../../src/vault/transport/guardian';
+
+describe('GuardianClient', () => {
+  it('constructs with endpoint', () => {
+    const client = new GuardianClient({ address: '127.0.0.1', port: 7500 });
+    expect(client).toBeDefined();
+  });
+
+  it('session token management', () => {
+    const client = new GuardianClient({ address: '127.0.0.1', port: 7500 });
+    expect(client.getSessionToken()).toBeNull();
+
+    client.setSessionToken('test-token');
+    expect(client.getSessionToken()).toBe('test-token');
+
+    client.clearSessionToken();
+    expect(client.getSessionToken()).toBeNull();
+  });
+
+  it('GuardianError has code and message', () => {
+    const err = new GuardianError('TIMEOUT', 'request timed out');
+    expect(err.code).toBe('TIMEOUT');
+    expect(err.message).toBe('request timed out');
+    expect(err.name).toBe('GuardianError');
+    expect(err instanceof Error).toBe(true);
+  });
+
+  it('putSecret throws without session token', async () => {
+    const client = new GuardianClient({ address: '127.0.0.1', port: 7500 });
+    await expect(client.putSecret('test', new Uint8Array([1]), 1)).rejects.toThrow('No session token');
+  });
+
+  it('getSecret throws without session token', async () => {
+    const client = new GuardianClient({ address: '127.0.0.1', port: 7500 });
+    await expect(client.getSecret('test')).rejects.toThrow('No session token');
+  });
+
+  it('deleteSecret throws without session token', async () => {
+    const client = new GuardianClient({ address: '127.0.0.1', port: 7500 });
+    await expect(client.deleteSecret('test')).rejects.toThrow('No session token');
+  });
+
+  it('listSecrets throws without session token', async () => {
+    const client = new GuardianClient({ address: '127.0.0.1', port: 7500 });
+    await expect(client.listSecrets()).rejects.toThrow('No session token');
+  });
+});
diff --git a/tests/unit/vault/client.test.ts b/tests/unit/vault/client.test.ts
new file mode 100644
index 0000000..0850528
--- /dev/null
+++ b/tests/unit/vault/client.test.ts
@@ -0,0 +1,22 @@
+import { describe, it, expect } from 'vitest';
+import { VaultClient } from '../../../src/vault/client';
+
+describe('VaultClient', () => {
+  it('constructs with config', () => {
+    const client = new VaultClient({
+      guardians: [{ address: '127.0.0.1', port: 7500 }],
+      hmacKey: new Uint8Array(32),
+      identityHex: 'a'.repeat(64),
+    });
+    expect(client).toBeDefined();
+  });
+
+  it('clearSessions does not throw', () => {
+    const client = new VaultClient({
+      guardians: [],
+      hmacKey: new Uint8Array(32),
+      identityHex: 'b'.repeat(64),
+    });
+    expect(() => client.clearSessions()).not.toThrow();
+  });
+});
diff --git a/tests/unit/vault/quorum.test.ts b/tests/unit/vault/quorum.test.ts
new file mode 100644
index 0000000..e7913cf
--- /dev/null
+++ b/tests/unit/vault/quorum.test.ts
@@ -0,0 +1,57 @@
+import { describe, it, expect } from 'vitest';
+import { adaptiveThreshold, writeQuorum } from '../../../src/vault/quorum';
+
+describe('adaptiveThreshold', () => {
+  it('returns max(3, floor(N/3))', () => {
+    expect(adaptiveThreshold(3)).toBe(3);
+    expect(adaptiveThreshold(9)).toBe(3);
+    expect(adaptiveThreshold(12)).toBe(4);
+    expect(adaptiveThreshold(30)).toBe(10);
+    expect(adaptiveThreshold(100)).toBe(33);
+  });
+
+  it('minimum is 3', () => {
+    for (let n = 0; n <= 9; n++) {
+      expect(adaptiveThreshold(n)).toBeGreaterThanOrEqual(3);
+    }
+  });
+
+  it('monotonically non-decreasing', () => {
+    let prev = adaptiveThreshold(0);
+    for (let n = 1; n <= 255; n++) {
+      const current = adaptiveThreshold(n);
+      expect(current).toBeGreaterThanOrEqual(prev);
+      prev = current;
+    }
+  });
+});
+
+describe('writeQuorum', () => {
+  it('returns ceil(2N/3) for N >= 3', () => {
+    expect(writeQuorum(3)).toBe(2);
+    expect(writeQuorum(6)).toBe(4);
+    expect(writeQuorum(10)).toBe(7);
+    expect(writeQuorum(100)).toBe(67);
+  });
+
+  it('returns 0 for N=0', () => {
+    expect(writeQuorum(0)).toBe(0);
+  });
+
+  it('returns N for N <= 2', () => {
+    expect(writeQuorum(1)).toBe(1);
+    expect(writeQuorum(2)).toBe(2);
+  });
+
+  it('always > N/2 for N >= 3', () => {
+    for (let n = 3; n <= 255; n++) {
+      expect(writeQuorum(n)).toBeGreaterThan(n / 2);
+    }
+  });
+
+  it('never exceeds N', () => {
+    for (let n = 0; n <= 255; n++) {
+      expect(writeQuorum(n)).toBeLessThanOrEqual(n);
+    }
+  });
+});