feat: implement CookieBridge M1 — core protocol & relay server

- Protocol spec: encrypted envelope format, device identity (Ed25519 + X25519),
  LWW conflict resolution with Lamport clocks
- E2E encryption: XChaCha20-Poly1305 via sodium-native, X25519 key exchange
- WebSocket relay server: stateless message forwarding, device auth via
  challenge-response, offline message queuing, ping/pong keepalive
- Device pairing: time-limited pairing codes, key exchange broker via HTTP
- Sync protocol: envelope builder/opener, conflict-resolving cookie store
- 31 tests passing (crypto, pairing, conflict resolution, full integration)

Co-Authored-By: Paperclip <noreply@paperclip.ing>

projects/cookiebridge/tests/pairing.test.ts

@@ -0,0 +1,57 @@
+import { describe, it, expect } from "vitest";
+import { PairingStore, generatePairingCode } from "../src/pairing/index.js";
+
+describe("PairingStore", () => {
+  it("creates and finds a pairing session", () => {
+    const store = new PairingStore();
+    const session = store.create("device-a-id", "device-a-x25519-pub");
+    expect(session.pairingCode).toHaveLength(6);
+    expect(session.deviceId).toBe("device-a-id");
+
+    const found = store.find(session.pairingCode);
+    expect(found).not.toBeNull();
+    expect(found!.deviceId).toBe("device-a-id");
+  });
+
+  it("consumes a session (one-time use)", () => {
+    const store = new PairingStore();
+    const session = store.create("d1", "pub1");
+
+    const consumed = store.consume(session.pairingCode);
+    expect(consumed).not.toBeNull();
+    expect(consumed!.deviceId).toBe("d1");
+
+    // Second consume returns null
+    const again = store.consume(session.pairingCode);
+    expect(again).toBeNull();
+  });
+
+  it("returns null for unknown code", () => {
+    const store = new PairingStore();
+    expect(store.find("999999")).toBeNull();
+  });
+
+  it("expires sessions after TTL", () => {
+    const store = new PairingStore();
+    const session = store.create("d1", "pub1");
+
+    // Manually expire by setting expiresAt in the past
+    // We access the internal session via find and mutate it
+    const found = store.find(session.pairingCode);
+    if (found) {
+      (found as { expiresAt: number }).expiresAt = Date.now() - 1000;
+    }
+
+    expect(store.find(session.pairingCode)).toBeNull();
+  });
+});
+
+describe("generatePairingCode", () => {
+  it("generates 6-digit codes", () => {
+    for (let i = 0; i < 20; i++) {
+      const code = generatePairingCode();
+      expect(code).toHaveLength(6);
+      expect(/^\d{6}$/.test(code)).toBe(true);
+    }
+  });
+});