diff --git a/api/__tests__/lib/codes.test.ts b/api/__tests__/lib/codes.test.ts
new file mode 100644
index 0000000..5d96569
--- /dev/null
+++ b/api/__tests__/lib/codes.test.ts
@@ -0,0 +1,36 @@
+import { describe, it, expect } from 'vitest';
+import { generateHmacSecret, generatePairingCode, generateToken, isHttpsUrl } from '../../src/lib/codes.ts';
+
+describe('generatePairingCode', () => {
+  it('returns an 8-char A-Z0-9 code', () => {
+    expect(generatePairingCode()).toMatch(/^[A-Z0-9]{8}$/);
+  });
+
+  it('returns distinct codes across calls', () => {
+    const seen = new Set(Array.from({ length: 50 }, () => generatePairingCode()));
+    expect(seen.size).toBeGreaterThan(40);
+  });
+});
+
+describe('generateToken / generateHmacSecret', () => {
+  it('returns a 32-byte base64url token', () => {
+    const token = generateToken();
+    expect(token).toMatch(/^[A-Za-z0-9_-]{43}$/);
+    expect(token).not.toEqual(generateToken());
+  });
+
+  it('returns a distinct hmac secret', () => {
+    expect(generateHmacSecret()).not.toEqual(generateHmacSecret());
+  });
+});
+
+describe('isHttpsUrl', () => {
+  it('accepts https URLs', () => {
+    expect(isHttpsUrl('https://example.com')).toBe(true);
+  });
+
+  it('rejects http and malformed URLs', () => {
+    expect(isHttpsUrl('http://example.com')).toBe(false);
+    expect(isHttpsUrl('not-a-url')).toBe(false);
+  });
+});
diff --git a/api/__tests__/routes/sites-pair.test.ts b/api/__tests__/routes/sites-pair.test.ts
new file mode 100644
index 0000000..fd5376f
--- /dev/null
+++ b/api/__tests__/routes/sites-pair.test.ts
@@ -0,0 +1,92 @@
+import { describe, it, expect } from 'vitest';
+import type { FastifyInstance } from 'fastify';
+import { buildApp } from '../../src/app.ts';
+
+async function signup(app: FastifyInstance): Promise<string> {
+  const res = await app.inject({
+    method: 'POST',
+    url: '/auth/signup',
+    payload: { email: `a-${Date.now()}@example.com`, password: 'password123' },
+  });
+  return res.json().sessionToken as string;
+}
+
+describe('sites pairing flow', () => {
+  it('requires a session to pair', async () => {
+    const app = await buildApp();
+    const res = await app.inject({ method: 'POST', url: '/sites/pair' });
+    expect(res.statusCode).toBe(401);
+  });
+
+  it('redeems a code once, binds site_url, and returns tokens', async () => {
+    const app = await buildApp();
+    const token = await signup(app);
+
+    const pair = await app.inject({
+      method: 'POST',
+      url: '/sites/pair',
+      headers: { authorization: `Bearer ${token}` },
+    });
+    expect(pair.statusCode).toBe(201);
+    const { code } = pair.json();
+
+    const redeem = await app.inject({
+      method: 'POST',
+      url: '/sites/redeem',
+      payload: { code, siteUrl: 'https://example.com' },
+    });
+    expect(redeem.statusCode).toBe(201);
+    const body = redeem.json();
+    expect(body.siteId).toBeTruthy();
+    expect(body.readToken).toBeTruthy();
+    expect(body.deployToken).toBeTruthy();
+    expect(body.hmacSecret).toBeTruthy();
+
+    const second = await app.inject({
+      method: 'POST',
+      url: '/sites/redeem',
+      payload: { code, siteUrl: 'https://example.com' },
+    });
+    expect(second.statusCode).toBe(400);
+  });
+
+  it('does not mark the site connected until confirmed', async () => {
+    const app = await buildApp();
+    const token = await signup(app);
+
+    const pair = await app.inject({
+      method: 'POST',
+      url: '/sites/pair',
+      headers: { authorization: `Bearer ${token}` },
+    });
+    const { code } = pair.json();
+
+    const redeem = await app.inject({
+      method: 'POST',
+      url: '/sites/redeem',
+      payload: { code, siteUrl: 'https://example.com' },
+    });
+    const { siteId } = redeem.json();
+
+    const before = await app.inject({
+      method: 'GET',
+      url: `/sites/${siteId}`,
+      headers: { authorization: `Bearer ${token}` },
+    });
+    expect(before.json().connected).toBe(false);
+
+    const confirm = await app.inject({
+      method: 'POST',
+      url: `/sites/${siteId}/confirm`,
+      headers: { authorization: `Bearer ${token}` },
+    });
+    expect(confirm.statusCode).toBe(200);
+
+    const after = await app.inject({
+      method: 'GET',
+      url: `/sites/${siteId}`,
+      headers: { authorization: `Bearer ${token}` },
+    });
+    expect(after.json().connected).toBe(true);
+  });
+});
diff --git a/api/__tests__/services/pairing-service.test.ts b/api/__tests__/services/pairing-service.test.ts
new file mode 100644
index 0000000..ae5d517
--- /dev/null
+++ b/api/__tests__/services/pairing-service.test.ts
@@ -0,0 +1,59 @@
+import { describe, it, expect } from 'vitest';
+import { PairingService } from '../../src/services/pairing-service.ts';
+
+describe('PairingService', () => {
+  it('issues an 8-char code with a 5-minute expiry', () => {
+    const svc = new PairingService({ now: () => 1_000_000 });
+    const { code, expiresAt } = svc.issue('acct-1');
+    expect(code).toMatch(/^[A-Z0-9]{8}$/);
+    expect(expiresAt).toBe(1_000_000 + 5 * 60 * 1000);
+  });
+
+  it('redeems a valid code once and returns distinct scoped tokens', () => {
+    const svc = new PairingService({ now: () => 1_000_000 });
+    const { code } = svc.issue('acct-1');
+    const result = svc.redeem(code, 'https://example.com');
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.accountId).toBe('acct-1');
+      expect(result.readToken).toBeTruthy();
+      expect(result.deployToken).toBeTruthy();
+      expect(result.hmacSecret).toBeTruthy();
+      expect(result.readToken).not.toBe(result.deployToken);
+    }
+  });
+
+  it('rejects a second redeem of the same code', () => {
+    const svc = new PairingService({ now: () => 1_000_000 });
+    const { code } = svc.issue('acct-1');
+    svc.redeem(code, 'https://example.com');
+    expect(svc.redeem(code, 'https://example.com')).toEqual({ ok: false, error: 'consumed' });
+  });
+
+  it('expires a code after five minutes', () => {
+    let t = 1_000_000;
+    const svc = new PairingService({ now: () => t });
+    const { code } = svc.issue('acct-1');
+    t += 5 * 60 * 1000 + 1;
+    expect(svc.redeem(code, 'https://example.com')).toEqual({ ok: false, error: 'expired' });
+  });
+
+  it('locks a code after five failed attempts', () => {
+    const svc = new PairingService({ now: () => 1_000_000 });
+    const { code } = svc.issue('acct-1');
+    for (let i = 0; i < 5; i += 1) {
+      svc.redeem(code, 'http://insecure.example.com');
+    }
+    expect(svc.redeem(code, 'https://example.com')).toEqual({ ok: false, error: 'locked' });
+  });
+
+  it('rejects a non-https site URL as an invalid attempt', () => {
+    const svc = new PairingService({ now: () => 1_000_000 });
+    const { code } = svc.issue('acct-1');
+    expect(svc.redeem(code, 'http://insecure.example.com')).toEqual({ ok: false, error: 'invalid' });
+  });
+
+  it('returns invalid for an unknown code', () => {
+    expect(new PairingService().redeem('NOPE0000', 'https://example.com')).toEqual({ ok: false, error: 'invalid' });
+  });
+});
diff --git a/api/__tests__/services/plugin-client.test.ts b/api/__tests__/services/plugin-client.test.ts
new file mode 100644
index 0000000..ae261d4
--- /dev/null
+++ b/api/__tests__/services/plugin-client.test.ts
@@ -0,0 +1,59 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import { createHash, createHmac } from 'node:crypto';
+import { PluginClient } from '../../src/services/plugin-client.ts';
+
+let fetchMock: ReturnType<typeof vi.fn>;
+
+beforeEach(() => {
+  fetchMock = vi.fn();
+  vi.stubGlobal('fetch', fetchMock);
+});
+
+afterEach(() => {
+  vi.unstubAllGlobals();
+});
+
+const creds = { siteUrl: 'https://example.com', readToken: 'r-token', hmacSecret: 'h-secret' };
+
+function expectedSignature(secret: string, timestamp: string, method: string, path: string, body: string): string {
+  const canonical = `${timestamp}\n${method}\n${path}\n${createHash('sha256').update(body).digest('hex')}`;
+  return createHmac('sha256', secret).update(canonical).digest('hex');
+}
+
+describe('PluginClient', () => {
+  it('signs requests and sends the token in Authorization, never the URL', async () => {
+    fetchMock.mockResolvedValue({ ok: true, json: async () => ({ theme: 'twentytwentyfour' }) });
+    const client = new PluginClient(creds);
+
+    await client.get('/site-info');
+
+    const [url, init] = fetchMock.mock.calls[0] as [string, { headers: Record<string, string> }];
+    expect(url).toBe('https://example.com/wp-json/wursor/v1/site-info');
+    expect(String(url)).not.toContain('r-token');
+    expect(init.headers.Authorization).toBe('Bearer r-token');
+    expect(init.headers['X-Wursor-Timestamp']).toBeTruthy();
+    expect(init.headers['X-Wursor-Signature']).toMatch(/^[0-9a-f]{64}$/);
+  });
+
+  it('computes the HMAC over timestamp + method + path + body hash', async () => {
+    fetchMock.mockResolvedValue({ ok: true, json: async () => ({}) });
+    const client = new PluginClient(creds);
+
+    await client.post('/files', { a: 1 });
+
+    const [, init] = fetchMock.mock.calls[0] as [string, { headers: Record<string, string> }];
+    const ts = init.headers['X-Wursor-Timestamp'];
+    expect(init.headers['X-Wursor-Signature']).toBe(expectedSignature('h-secret', ts, 'POST', '/files', '{"a":1}'));
+  });
+
+  it('maps a 401 to Authentication failed', async () => {
+    fetchMock.mockResolvedValue({ ok: false, status: 401 });
+    const client = new PluginClient(creds);
+
+    await expect(client.get('/site-info')).rejects.toThrow('Authentication failed');
+  });
+
+  it('refuses to construct a client with an http:// site URL', () => {
+    expect(() => new PluginClient({ ...creds, siteUrl: 'http://example.com' })).toThrow();
+  });
+});
diff --git a/api/src/app.ts b/api/src/app.ts
index cfa9860..7b9427f 100644
--- a/api/src/app.ts
+++ b/api/src/app.ts
@@ -1,19 +1,31 @@
 import Fastify from 'fastify';
 import { authRoutes } from './routes/auth.ts';
 import { sessionRoutes } from './routes/sessions.ts';
+import { siteRoutes } from './routes/sites.ts';
+import { PairingService } from './services/pairing-service.ts';
+import { InMemorySessionStore, type SessionStore } from './services/session-store.ts';
+import { InMemorySiteStore, type SiteStore } from './services/site-store.ts';
 import { InMemoryUserStore, type UserStore } from './services/user-store.ts';
 import type { SandboxManager } from './services/sandbox-manager.ts';
 
 export type BuildAppOptions = {
   userStore?: UserStore;
+  sessionStore?: SessionStore;
+  siteStore?: SiteStore;
+  pairingService?: PairingService;
   sandboxManager?: SandboxManager;
 };
 
 export async function buildApp(opts: BuildAppOptions = {}) {
   const app = Fastify();
-  const store = opts.userStore ?? new InMemoryUserStore();
+  const userStore = opts.userStore ?? new InMemoryUserStore();
+  const sessionStore = opts.sessionStore ?? new InMemorySessionStore();
+  const siteStore = opts.siteStore ?? new InMemorySiteStore();
+  const pairingService = opts.pairingService ?? new PairingService();
+
   app.get('/health', async () => ({ ok: true }));
-  await authRoutes(app, store);
+  await authRoutes(app, userStore, sessionStore);
   await sessionRoutes(app, opts.sandboxManager);
+  await siteRoutes(app, { sessionStore, siteStore, pairingService });
   return app;
 }
diff --git a/api/src/lib/codes.ts b/api/src/lib/codes.ts
new file mode 100644
index 0000000..9ddcfde
--- /dev/null
+++ b/api/src/lib/codes.ts
@@ -0,0 +1,28 @@
+import { randomBytes, randomInt } from 'node:crypto';
+
+const CODE_ALPHABET = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
+const CODE_LENGTH = 8;
+
+export function generatePairingCode(): string {
+  let code = '';
+  for (let i = 0; i < CODE_LENGTH; i += 1) {
+    code += CODE_ALPHABET[randomInt(CODE_ALPHABET.length)];
+  }
+  return code;
+}
+
+export function generateToken(): string {
+  return randomBytes(32).toString('base64url');
+}
+
+export function generateHmacSecret(): string {
+  return randomBytes(32).toString('base64url');
+}
+
+export function isHttpsUrl(value: string): boolean {
+  try {
+    return new URL(value).protocol === 'https:';
+  } catch {
+    return false;
+  }
+}
diff --git a/api/src/middleware/auth.ts b/api/src/middleware/auth.ts
new file mode 100644
index 0000000..3487f04
--- /dev/null
+++ b/api/src/middleware/auth.ts
@@ -0,0 +1,25 @@
+import type { FastifyReply, FastifyRequest } from 'fastify';
+import type { SessionStore } from '../services/session-store.ts';
+
+declare module 'fastify' {
+  interface FastifyRequest {
+    userId?: string;
+  }
+}
+
+export function requireSession(store: SessionStore) {
+  return async (request: FastifyRequest, reply: FastifyReply): Promise<void> => {
+    const header = request.headers.authorization;
+    const token = header !== undefined && header.startsWith('Bearer ') ? header.slice('Bearer '.length) : undefined;
+    if (token === undefined) {
+      await reply.status(401).send({ error: 'unauthorized' });
+      return;
+    }
+    const session = await store.findByToken(token);
+    if (session === undefined) {
+      await reply.status(401).send({ error: 'unauthorized' });
+      return;
+    }
+    request.userId = session.userId;
+  };
+}
diff --git a/api/src/routes/auth.ts b/api/src/routes/auth.ts
index 9a868c3..283c578 100644
--- a/api/src/routes/auth.ts
+++ b/api/src/routes/auth.ts
@@ -1,5 +1,6 @@
 import type { FastifyInstance } from 'fastify';
-import { hashPassword, newId, newToken } from '../lib/crypto.ts';
+import { hashPassword, newId } from '../lib/crypto.ts';
+import type { SessionStore } from '../services/session-store.ts';
 import type { UserStore } from '../services/user-store.ts';
 
 const EMAIL_RE = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
@@ -9,7 +10,11 @@ type SignupBody = {
   password?: string;
 };
 
-export async function authRoutes(app: FastifyInstance, store: UserStore): Promise<void> {
+export async function authRoutes(
+  app: FastifyInstance,
+  store: UserStore,
+  sessionStore: SessionStore,
+): Promise<void> {
   app.post('/auth/signup', async (request, reply) => {
     const { email: rawEmail, password } = request.body as SignupBody;
     const email = rawEmail?.trim().toLowerCase();
@@ -25,6 +30,7 @@ export async function authRoutes(app: FastifyInstance, store: UserStore): Promis
     }
 
     const user = await store.create({ id: newId(), email, passwordHash: hashPassword(password) });
-    return reply.status(201).send({ user: { id: user.id, email: user.email }, sessionToken: newToken() });
+    const session = await sessionStore.create(user.id);
+    return reply.status(201).send({ user: { id: user.id, email: user.email }, sessionToken: session.token });
   });
 }
diff --git a/api/src/routes/sites.ts b/api/src/routes/sites.ts
new file mode 100644
index 0000000..b6341b1
--- /dev/null
+++ b/api/src/routes/sites.ts
@@ -0,0 +1,67 @@
+import type { FastifyInstance } from 'fastify';
+import { requireSession } from '../middleware/auth.ts';
+import { newId } from '../lib/crypto.ts';
+import type { PairingService } from '../services/pairing-service.ts';
+import type { SessionStore } from '../services/session-store.ts';
+import type { SiteStore } from '../services/site-store.ts';
+
+export type SiteRoutesDeps = {
+  sessionStore: SessionStore;
+  pairingService: PairingService;
+  siteStore: SiteStore;
+};
+
+type RedeemBody = {
+  code?: string;
+  siteUrl?: string;
+};
+
+export async function siteRoutes(app: FastifyInstance, deps: SiteRoutesDeps): Promise<void> {
+  app.post('/sites/pair', { preHandler: requireSession(deps.sessionStore) }, async (request, reply) => {
+    const { code, expiresAt } = deps.pairingService.issue(request.userId as string);
+    return reply.status(201).send({ code, expiresAt });
+  });
+
+  app.post('/sites/redeem', async (request, reply) => {
+    const { code, siteUrl } = request.body as RedeemBody;
+    if (code === undefined || siteUrl === undefined) {
+      return reply.status(400).send({ error: 'invalid' });
+    }
+    const result = deps.pairingService.redeem(code, siteUrl);
+    if (!result.ok) {
+      return reply.status(400).send({ error: result.error });
+    }
+    const site = await deps.siteStore.create({
+      id: newId(),
+      accountId: result.accountId,
+      siteUrl: result.siteUrl,
+      readToken: result.readToken,
+      deployToken: result.deployToken,
+      hmacSecret: result.hmacSecret,
+      connected: false,
+    });
+    return reply.status(201).send({
+      siteId: site.id,
+      readToken: site.readToken,
+      deployToken: site.deployToken,
+      hmacSecret: site.hmacSecret,
+    });
+  });
+
+  app.get('/sites/:siteId', { preHandler: requireSession(deps.sessionStore) }, async (request, reply) => {
+    const site = await deps.siteStore.findById((request.params as { siteId: string }).siteId);
+    if (site === undefined || site.accountId !== request.userId) {
+      return reply.status(404).send({ error: 'not_found' });
+    }
+    return { id: site.id, siteUrl: site.siteUrl, connected: site.connected };
+  });
+
+  app.post('/sites/:siteId/confirm', { preHandler: requireSession(deps.sessionStore) }, async (request, reply) => {
+    const site = await deps.siteStore.findById((request.params as { siteId: string }).siteId);
+    if (site === undefined || site.accountId !== request.userId) {
+      return reply.status(404).send({ error: 'not_found' });
+    }
+    await deps.siteStore.setConnected(site.id, true);
+    return { connected: true };
+  });
+}
diff --git a/api/src/services/pairing-service.ts b/api/src/services/pairing-service.ts
new file mode 100644
index 0000000..d79efef
--- /dev/null
+++ b/api/src/services/pairing-service.ts
@@ -0,0 +1,78 @@
+import { generateHmacSecret, generatePairingCode, generateToken, isHttpsUrl } from '../lib/codes.ts';
+
+export type PendingPairing = {
+  code: string;
+  accountId: string;
+  expiresAt: number;
+  attempts: number;
+  locked: boolean;
+  consumed: boolean;
+};
+
+export type RedeemError = 'invalid' | 'expired' | 'locked' | 'consumed';
+
+export type RedeemResult =
+  | { ok: true; accountId: string; siteUrl: string; readToken: string; deployToken: string; hmacSecret: string }
+  | { ok: false; error: RedeemError };
+
+export type PairingServiceOptions = {
+  ttlMs?: number;
+  maxAttempts?: number;
+  now?: () => number;
+};
+
+const DEFAULT_TTL_MS = 5 * 60 * 1000;
+const DEFAULT_MAX_ATTEMPTS = 5;
+
+export class PairingService {
+  private readonly pending = new Map<string, PendingPairing>();
+  private readonly now: () => number;
+  private readonly ttlMs: number;
+  private readonly maxAttempts: number;
+
+  constructor(opts: PairingServiceOptions = {}) {
+    this.now = opts.now ?? Date.now;
+    this.ttlMs = opts.ttlMs ?? DEFAULT_TTL_MS;
+    this.maxAttempts = opts.maxAttempts ?? DEFAULT_MAX_ATTEMPTS;
+  }
+
+  issue(accountId: string): { code: string; expiresAt: number } {
+    const code = generatePairingCode();
+    const expiresAt = this.now() + this.ttlMs;
+    this.pending.set(code, { code, accountId, expiresAt, attempts: 0, locked: false, consumed: false });
+    return { code, expiresAt };
+  }
+
+  redeem(code: string, siteUrl: string): RedeemResult {
+    const pairing = this.pending.get(code);
+    if (pairing === undefined) {
+      return { ok: false, error: 'invalid' };
+    }
+    if (pairing.consumed) {
+      return { ok: false, error: 'consumed' };
+    }
+    if (pairing.locked) {
+      return { ok: false, error: 'locked' };
+    }
+    if (this.now() > pairing.expiresAt) {
+      return { ok: false, error: 'expired' };
+    }
+    if (!isHttpsUrl(siteUrl)) {
+      pairing.attempts += 1;
+      if (pairing.attempts >= this.maxAttempts) {
+        pairing.locked = true;
+      }
+      return { ok: false, error: 'invalid' };
+    }
+
+    pairing.consumed = true;
+    return {
+      ok: true,
+      accountId: pairing.accountId,
+      siteUrl,
+      readToken: generateToken(),
+      deployToken: generateToken(),
+      hmacSecret: generateHmacSecret(),
+    };
+  }
+}
diff --git a/api/src/services/plugin-client.ts b/api/src/services/plugin-client.ts
new file mode 100644
index 0000000..1ef8a79
--- /dev/null
+++ b/api/src/services/plugin-client.ts
@@ -0,0 +1,64 @@
+import { createHash, createHmac } from 'node:crypto';
+import { isHttpsUrl } from '../lib/codes.ts';
+
+export type PluginCredentials = {
+  siteUrl: string;
+  readToken: string;
+  deployToken?: string;
+  hmacSecret: string;
+};
+
+function sha256hex(value: string): string {
+  return createHash('sha256').update(value).digest('hex');
+}
+
+export class PluginClient {
+  private readonly baseUrl: string;
+
+  constructor(private readonly creds: PluginCredentials) {
+    if (!isHttpsUrl(creds.siteUrl)) {
+      throw new Error('Site URL must be https');
+    }
+    this.baseUrl = `${creds.siteUrl.replace(/\/$/, '')}/wp-json/wursor/v1`;
+  }
+
+  async get(path: string): Promise<unknown> {
+    return this.request('GET', path);
+  }
+
+  async post(path: string, body?: unknown): Promise<unknown> {
+    return this.request('POST', path, body);
+  }
+
+  private async request(method: string, path: string, body?: unknown): Promise<unknown> {
+    const bodyText = body === undefined ? '' : JSON.stringify(body);
+    const timestamp = String(Math.floor(Date.now() / 1000));
+    const canonical = `${timestamp}\n${method}\n${path}\n${sha256hex(bodyText)}`;
+    const signature = createHmac('sha256', this.creds.hmacSecret).update(canonical).digest('hex');
+
+    const token = method === 'GET' ? this.creds.readToken : (this.creds.deployToken ?? this.creds.readToken);
+
+    const headers: Record<string, string> = {
+      Authorization: `Bearer ${token}`,
+      'X-Wursor-Timestamp': timestamp,
+      'X-Wursor-Signature': signature,
+    };
+    if (bodyText !== '') {
+      headers['Content-Type'] = 'application/json';
+    }
+
+    const res = await fetch(`${this.baseUrl}${path}`, {
+      method,
+      headers,
+      body: bodyText === '' ? undefined : bodyText,
+    });
+
+    if (!res.ok) {
+      if (res.status === 401) {
+        throw new Error('Authentication failed');
+      }
+      throw new Error(`Plugin HTTP ${res.status}`);
+    }
+    return res.json();
+  }
+}
diff --git a/api/src/services/session-store.ts b/api/src/services/session-store.ts
new file mode 100644
index 0000000..baed11d
--- /dev/null
+++ b/api/src/services/session-store.ts
@@ -0,0 +1,26 @@
+import { generateToken } from '../lib/codes.ts';
+
+export type Session = {
+  token: string;
+  userId: string;
+  createdAt: number;
+};
+
+export interface SessionStore {
+  create(userId: string): Promise<Session>;
+  findByToken(token: string): Promise<Session | undefined>;
+}
+
+export class InMemorySessionStore implements SessionStore {
+  private byToken = new Map<string, Session>();
+
+  async create(userId: string): Promise<Session> {
+    const session = { token: generateToken(), userId, createdAt: Date.now() };
+    this.byToken.set(session.token, session);
+    return session;
+  }
+
+  async findByToken(token: string): Promise<Session | undefined> {
+    return this.byToken.get(token);
+  }
+}
diff --git a/api/src/services/site-store.ts b/api/src/services/site-store.ts
new file mode 100644
index 0000000..b8d01b1
--- /dev/null
+++ b/api/src/services/site-store.ts
@@ -0,0 +1,35 @@
+export type Site = {
+  id: string;
+  accountId: string;
+  siteUrl: string;
+  readToken: string;
+  deployToken: string;
+  hmacSecret: string;
+  connected: boolean;
+};
+
+export interface SiteStore {
+  create(site: Site): Promise<Site>;
+  findById(id: string): Promise<Site | undefined>;
+  setConnected(id: string, connected: boolean): Promise<void>;
+}
+
+export class InMemorySiteStore implements SiteStore {
+  private byId = new Map<string, Site>();
+
+  async create(site: Site): Promise<Site> {
+    this.byId.set(site.id, site);
+    return site;
+  }
+
+  async findById(id: string): Promise<Site | undefined> {
+    return this.byId.get(id);
+  }
+
+  async setConnected(id: string, connected: boolean): Promise<void> {
+    const site = this.byId.get(id);
+    if (site !== undefined) {
+      this.byId.set(id, { ...site, connected });
+    }
+  }
+}
diff --git a/docs/decisions/0016-pairing-code-ownership.md b/docs/decisions/0016-pairing-code-ownership.md
new file mode 100644
index 0000000..52644c0
--- /dev/null
+++ b/docs/decisions/0016-pairing-code-ownership.md
@@ -0,0 +1,26 @@
+# 16. Pairing-code TTL/lockout lives on the Wursor API; the plugin enforces token/HMAC/scope
+
+- **Status:** Accepted
+- **Date:** 2026-08-15
+
+## Context
+
+The pairing threat model (`spikes/pairing-threat-model.md`) mandates that **Wursor generates** the pairing code and **the plugin redeems** it — explicitly rejecting the plugin-local generate/redeem sketch in IMPLEMENTATION. Its "Sprint 2 tests" section, however, still labels the pairing-code TTL/lockout/single-use tests under `plugin/__tests__/test-auth.php`, a leftover from that rejected sketch.
+
+## Decision
+
+The pairing code lifecycle (issue, 5-minute TTL, 5-attempt lockout, single-use, `site_url` https check) is enforced in the API's `PairingService`. The plugin's `class-auth.php` enforces token hashing (SHA-256 + `hash_equals`), HMAC verification, `read` vs `deploy` scoping, and rotation.
+
+### Options considered
+
+- Follow the test-file labels literally (plugin enforces the pairing code).
+- Follow the locked flow (chosen).
+
+### Rejected
+
+- Literal labels — they contradict the "Wursor generates, plugin redeems" flow the same note mandates; pairing state can only live where the code is issued.
+
+## Consequences
+
+- `api/__tests__/routes/sites-pair.test.ts` + `pairing-service.test.ts` cover TTL/lockout/single-use.
+- `plugin/__tests__/test-auth.php` covers hashing, HMAC, scope, and rotation only.
diff --git a/docs/decisions/README.md b/docs/decisions/README.md
index c7571fb..fd53daf 100644
--- a/docs/decisions/README.md
+++ b/docs/decisions/README.md
@@ -29,6 +29,7 @@ Each ADR is a single file following the [Nygard format](https://cognitect.com/bl
 | [0013](0013-docker-boundary-mock.md) | Sandbox orchestration mocks the Docker boundary; real daemon client deferred | Accepted |
 | [0014](0014-postgres-queryable.md) | Postgres user store via a Queryable boundary; schema in SQL migrations | Accepted |
 | [0015](0015-dockerode-engine-gating.md) | Docker daemon client via dockerode behind an injected engine; sandbox gated by env | Accepted |
+| [0016](0016-pairing-code-ownership.md) | Pairing-code TTL/lockout lives on the Wursor API; the plugin enforces token/HMAC/scope | Accepted |
 
 ## How to add one