diff --git a/e2e/harness/dpop.ts b/e2e/harness/dpop.ts
new file mode 100644
index 0000000..d6bdd1b
--- /dev/null
+++ b/e2e/harness/dpop.ts
@@ -0,0 +1,141 @@
+/**
+ * P5 signing-key setup + capability-token / DPoP bundle builder. These wire the REAL
+ * relay-auth issue + DPoP primitives. `resetVerifyKeyForTest`, `resetDpopCacheForTest`,
+ * `buildDpopProof`, `jwkThumbprint`, and the WebCrypto Ed25519 helpers are TEST-ONLY / internal,
+ * so they are deep-imported from `relay-auth/src/...` (relay-auth has no `exports` map, so subpath
+ * imports resolve through the e2e node_modules symlink).
+ */
+import { randomUUID } from 'node:crypto'
+import { issueCapabilityToken, type DpopContext } from 'relay-auth'
+import type { CapabilityRight } from 'relay-contracts'
+import { encodeBase64UrlBytes } from 'relay-contracts'
+import {
+  configureVerifyKey,
+  resetVerifyKeyForTest,
+} from 'relay-auth/src/config/keys.js'
+import {
+  generateEd25519KeyPair,
+  exportEd25519PublicRaw,
+} from 'relay-auth/src/crypto/ed25519.js'
+import { buildDpopProof, resetDpopCacheForTest } from 'relay-auth/src/capability/verify.js'
+import { jwkThumbprint } from 'relay-auth/src/crypto/thumbprint.js'
+import { principal } from './fakes.js'
+
+export { resetDpopCacheForTest, jwkThumbprint }
+
+export interface P5Key {
+  readonly signingKey: CryptoKey
+  readonly publicRaw: Uint8Array
+}
+
+/** Configure the P5 verifying key globally and return the matching private signing key. */
+export async function setupP5SigningKey(): Promise<P5Key> {
+  resetVerifyKeyForTest()
+  const pair = await generateEd25519KeyPair()
+  configureVerifyKey(pair.publicKey)
+  const publicRaw = await exportEd25519PublicRaw(pair.publicKey)
+  return { signingKey: pair.privateKey, publicRaw }
+}
+
+export interface Ephemeral {
+  readonly privateKey: CryptoKey
+  readonly publicRaw: Uint8Array
+}
+
+export async function makeEphemeral(): Promise<Ephemeral> {
+  const pair = await generateEd25519KeyPair()
+  return { privateKey: pair.privateKey, publicRaw: await exportEd25519PublicRaw(pair.publicKey) }
+}
+
+export interface IssueOpts {
+  readonly accountId: string
+  readonly host: string
+  readonly aud: string
+  readonly rights?: readonly CapabilityRight[]
+  readonly ttl?: number
+  readonly now: number
+  readonly htu?: string
+  readonly htm?: string
+}
+
+/**
+ * A capability token bundled with a matching DPoP proof. `newDpop(at?)` mints a FRESH DPoP proof
+ * (new jti) bound to the SAME ephemeral key — needed to re-present the same token under a distinct
+ * DPoP (single-use jti / revocation tests) without tripping the DPoP replay cache.
+ */
+export interface CapBundle {
+  readonly raw: string
+  readonly dpop: DpopContext
+  readonly newDpop: (at?: number) => Promise<DpopContext>
+}
+
+export async function issueCapBundle(signingKey: CryptoKey, o: IssueOpts): Promise<CapBundle> {
+  const eph = await makeEphemeral()
+  const cnfJkt = await jwkThumbprint(eph.publicRaw)
+  const raw = await issueCapabilityToken(
+    {
+      principal: principal(o.accountId),
+      aud: o.aud,
+      host: o.host,
+      rights: o.rights ?? ['attach'],
+      ttlSeconds: o.ttl ?? 45,
+      cnfJkt,
+    },
+    signingKey,
+    o.now,
+  )
+  const htu = o.htu ?? `https://${o.aud}/ws`
+  const htm = o.htm ?? 'GET'
+  const newDpop = async (at: number = o.now): Promise<DpopContext> => ({
+    proofJws: await buildDpopProof(eph.privateKey, eph.publicRaw, {
+      htu,
+      htm,
+      jti: randomUUID(),
+      iat: at,
+    }),
+    htu,
+    htm,
+  })
+  return { raw, dpop: await newDpop(o.now), newDpop }
+}
+
+/**
+ * F4 crafting: a capability whose `cnf.jkt` is the thumbprint of a NON-32-byte blob, plus a DPoP
+ * proof whose `header.jwk.x` decodes to that same blob. The thumbprint check therefore PASSES and
+ * execution reaches `importEd25519PublicRaw(blob)`, which throws on the bad length — exercising the
+ * fail-safe (must resolve to false, never reject).
+ */
+export interface MalformedOpts {
+  readonly accountId: string
+  readonly host: string
+  readonly aud: string
+  readonly now: number
+  readonly blobLen?: number
+}
+
+export async function craftMalformedDpopBundle(
+  signingKey: CryptoKey,
+  o: MalformedOpts,
+): Promise<{ raw: string; dpop: DpopContext }> {
+  const blob = new Uint8Array(o.blobLen ?? 16).fill(7)
+  const cnfJkt = await jwkThumbprint(blob) // 43-char base64url regardless of blob length
+  const raw = await issueCapabilityToken(
+    {
+      principal: principal(o.accountId),
+      aud: o.aud,
+      host: o.host,
+      rights: ['attach'],
+      ttlSeconds: 45,
+      cnfJkt,
+    },
+    signingKey,
+    o.now,
+  )
+  const htu = `https://${o.aud}/ws`
+  const enc = (x: unknown): string =>
+    encodeBase64UrlBytes(new TextEncoder().encode(JSON.stringify(x)))
+  const h = enc({ typ: 'dpop+ed25519', jwk: { crv: 'Ed25519', kty: 'OKP', x: encodeBase64UrlBytes(blob) } })
+  const p = enc({ htu, htm: 'GET', jti: randomUUID(), iat: o.now })
+  const s = encodeBase64UrlBytes(new Uint8Array(64)) // arbitrary signature bytes
+  return { raw, dpop: { proofJws: `${h}.${p}.${s}`, htu, htm: 'GET' } }
+}
diff --git a/e2e/harness/fakes.ts b/e2e/harness/fakes.ts
new file mode 100644
index 0000000..3f3ac73
--- /dev/null
+++ b/e2e/harness/fakes.ts
@@ -0,0 +1,132 @@
+/**
+ * In-memory port fakes — the ONLY seams that stand in for the true I/O boundaries P1/P3 own
+ * (host registry / session registry / revocation store / token buckets / audit sink / revocation
+ * bus). Every security decision still runs through the REAL relay-auth exports; these fakes only
+ * supply storage. Adapted from `relay-auth/test/_helpers.ts` (same shapes, bare import paths).
+ */
+import type { HostRecord, KillSignal, RevocationBus } from 'relay-contracts'
+import type {
+  AuthenticatedPrincipal,
+  AuditEvent,
+  AuditSink,
+  HostRegistryPort,
+  SessionRegistryPort,
+  RevocationStore,
+  TokenBucketStore,
+} from 'relay-auth'
+
+/** An authenticated principal (the ONLY source of accountId, INV3). */
+export function principal(
+  accountId: string,
+  overrides: Partial<AuthenticatedPrincipal> = {},
+): AuthenticatedPrincipal {
+  return {
+    kind: 'human',
+    accountId,
+    principalId: 'cred-' + accountId,
+    amr: ['passkey'],
+    authAt: 1000,
+    stepUpAt: null,
+    ...overrides,
+  }
+}
+
+/** A minimal online HostRecord for the authz registry (agentPubkey here is unused by authz). */
+export function makeHostRecord(
+  accountId: string,
+  hostId: string,
+  status: HostRecord['status'] = 'online',
+): HostRecord {
+  return {
+    hostId,
+    accountId,
+    subdomain: 'sub-' + hostId,
+    agentPubkey: new Uint8Array(32),
+    enrollFpr: 'fpr-' + hostId,
+    status,
+    lastSeen: '2026-01-01T00:00:00.000Z',
+    createdAt: '2026-01-01T00:00:00.000Z',
+    revokedAt: null,
+  }
+}
+
+export function fakeHostRegistry(hosts: readonly HostRecord[]): HostRegistryPort {
+  const map = new Map(hosts.map((h) => [h.hostId, h]))
+  return { getById: async (id) => map.get(id) ?? null }
+}
+
+export interface MutableSessionRegistry extends SessionRegistryPort {
+  add(entry: { sessionId: string; hostId: string; accountId: string }): void
+}
+
+export function fakeSessionRegistry(
+  seed: readonly { sessionId: string; hostId: string; accountId: string }[] = [],
+): MutableSessionRegistry {
+  const map = new Map(seed.map((s) => [s.sessionId, { hostId: s.hostId, accountId: s.accountId }]))
+  return {
+    getById: async (id) => map.get(id) ?? null,
+    add: (e) => {
+      map.set(e.sessionId, { hostId: e.hostId, accountId: e.accountId })
+    },
+  }
+}
+
+export interface RevocationFake extends RevocationStore {
+  readonly revoked: Set<string>
+  readonly consumed: Set<string>
+}
+
+export function fakeRevocationStore(): RevocationFake {
+  const revoked = new Set<string>()
+  const consumed = new Set<string>()
+  return {
+    revoked,
+    consumed,
+    isRevoked: async (jti) => revoked.has(jti),
+    revokeJti: async (jti) => {
+      revoked.add(jti)
+    },
+    consumeOnce: async (jti) => {
+      if (consumed.has(jti)) return false
+      consumed.add(jti)
+      return true
+    },
+  }
+}
+
+export interface TokenBucketFake extends TokenBucketStore {
+  readonly blocked: Set<string>
+  readonly calls: string[]
+}
+
+/** Token bucket that always allows unless a key is added to `blocked`. */
+export function fakeTokenBucket(): TokenBucketFake {
+  const blocked = new Set<string>()
+  const calls: string[] = []
+  return {
+    blocked,
+    calls,
+    take: async (key) => {
+      calls.push(key)
+      return !blocked.has(key)
+    },
+  }
+}
+
+export interface AuditFake extends AuditSink {
+  readonly events: AuditEvent[]
+}
+
+export function fakeAuditSink(): AuditFake {
+  const events: AuditEvent[] = []
+  return { events, append: async (e) => void events.push(e) }
+}
+
+export interface RevocationBusFake extends RevocationBus {
+  readonly published: KillSignal[]
+}
+
+export function fakeRevocationBus(): RevocationBusFake {
+  const published: KillSignal[] = []
+  return { published, publish: async (s) => void published.push(s) }
+}
diff --git a/e2e/harness/spy.ts b/e2e/harness/spy.ts
new file mode 100644
index 0000000..a5d11e6
--- /dev/null
+++ b/e2e/harness/spy.ts
@@ -0,0 +1,34 @@
+/**
+ * RelaySpy — the untrusted-relay / attacker vantage. A passthrough that records every ciphertext
+ * byte it forwards (exactly what a malicious relay can see). INV2: a known plaintext marker must
+ * NEVER appear in `captured`. Mirrors the `relay-e2e/test/integration.test.ts` spy.
+ */
+import { MAX_FRAME_BYTES } from 'relay-e2e'
+
+export class RelaySpy {
+  readonly captured: Uint8Array[] = []
+
+  /** Forward a sealed payload, recording a copy of the ciphertext the relay observes. */
+  forward(payload: Uint8Array): Uint8Array {
+    if (payload.length > MAX_FRAME_BYTES) {
+      throw new Error(`payload exceeds MAX_FRAME_BYTES (${payload.length} > ${MAX_FRAME_BYTES})`)
+    }
+    this.captured.push(payload.slice())
+    return payload
+  }
+
+  /** Latin1 concatenation of everything the relay saw — for substring canary scans. */
+  snapshot(): string {
+    return this.captured.map((b) => Buffer.from(b).toString('latin1')).join(' ')
+  }
+
+  /** True if `marker` appears in ANY captured frame (utf8 or latin1) — INV2 tripwire. */
+  contains(marker: string): boolean {
+    if (this.snapshot().includes(marker)) return true
+    return this.captured.some(
+      (b) =>
+        Buffer.from(b).toString('utf8').includes(marker) ||
+        Buffer.from(b).toString('latin1').includes(marker),
+    )
+  }
+}
diff --git a/e2e/harness/world.ts b/e2e/harness/world.ts
new file mode 100644
index 0000000..18244a5
--- /dev/null
+++ b/e2e/harness/world.ts
@@ -0,0 +1,332 @@
+/**
+ * buildRelayWorld() — composes the REAL relay-auth (P5) + relay-e2e (P4) + agent (P2 replay)
+ * exports through the in-memory seams in ./fakes and exposes a clean flow API plus the untrusted
+ * "RelaySpy" attacker vantage. Only the true I/O boundaries are faked; every security check is the
+ * production code path. Pass an explicit `now` everywhere (no Date.now in assertions).
+ *
+ * The host identity used for the §4.4 handshake transcript signature is a real WebCrypto Ed25519
+ * key (relay-auth's own crypto, deep-imported) so the harness needs no @noble import of its own and
+ * no relay-e2e deep import (relay-e2e's `exports` map blocks subpaths).
+ */
+import { randomUUID, randomBytes } from 'node:crypto'
+import type { AeadAlg, E2EEnvelope, E2ESession, HostHello, HostRecord } from 'relay-contracts'
+import {
+  createClientHandshake,
+  createHostHandshake,
+  createE2ESession,
+  MemoryDevicePinStore,
+  deriveContentKey,
+  sealReplayFrame,
+  openReplayCiphertext,
+  encodeEnvelope,
+} from 'relay-e2e'
+import {
+  onUpgrade,
+  onReattach,
+  revoke,
+  revokeToken,
+  signDeviceAuthProof,
+  verifyDeviceProof,
+  type AuthzOutcome,
+  type EnforceDeps,
+  type UpgradeContext,
+  type StepUpPolicy,
+  type RevocationScope,
+} from 'relay-auth'
+import {
+  generateEd25519KeyPair,
+  exportEd25519PublicRaw,
+  importEd25519PublicRaw,
+  signEd25519,
+  verifyEd25519,
+} from 'relay-auth/src/crypto/ed25519.js'
+import { createReplaySealer, type ReplaySealer } from 'agent'
+import {
+  fakeAuditSink,
+  fakeHostRegistry,
+  fakeRevocationBus,
+  fakeRevocationStore,
+  fakeSessionRegistry,
+  fakeTokenBucket,
+  makeHostRecord,
+  principal,
+  type AuditFake,
+  type MutableSessionRegistry,
+  type RevocationBusFake,
+  type RevocationFake,
+  type TokenBucketFake,
+} from './fakes.js'
+import {
+  craftMalformedDpopBundle,
+  issueCapBundle,
+  resetDpopCacheForTest,
+  setupP5SigningKey,
+  type CapBundle,
+} from './dpop.js'
+import { RelaySpy } from './spy.js'
+
+export const DEFAULT_NOW = 1_700_000_000
+const REPLAY_ALG: AeadAlg = 'xchacha20-poly1305'
+
+export const NO_STEP_UP: StepUpPolicy = {
+  required: false,
+  maxAgeSeconds: Number.MAX_SAFE_INTEGER,
+  requiredMethod: 'passkey',
+}
+export const STRICT_PASSKEY: StepUpPolicy = {
+  required: true,
+  maxAgeSeconds: 300,
+  requiredMethod: 'passkey',
+}
+
+/** A seeded host: authz identity (hostId/accountId/aud) + §4.4 e2e identity + replay secret. */
+export interface HostFixture {
+  readonly label: string
+  readonly hostId: string
+  readonly accountId: string
+  readonly aud: string
+  readonly origin: string
+  readonly agentPubkey: Uint8Array
+  readonly hostContentSecret: Uint8Array
+  readonly replayAlg: AeadAlg
+  /** WebCrypto private key backing the handshake transcript signer. */
+  readonly signingPriv: CryptoKey
+}
+
+async function makeHostFixture(label: string, accountId: string): Promise<HostFixture> {
+  const kp = await generateEd25519KeyPair()
+  const agentPubkey = await exportEd25519PublicRaw(kp.publicKey)
+  const sub = `${label}.term.example.com`
+  return {
+    label,
+    hostId: randomUUID(),
+    accountId,
+    aud: sub,
+    origin: `https://${sub}`,
+    agentPubkey,
+    hostContentSecret: new Uint8Array(randomBytes(32)),
+    replayAlg: REPLAY_ALG,
+    signingPriv: kp.privateKey,
+  }
+}
+
+export interface UpgradeArgs {
+  readonly raw: string
+  readonly dpop: UpgradeContext['dpop']
+  readonly host: string
+  readonly aud: string
+  readonly origin: string
+  readonly now: number
+  readonly principal?: UpgradeContext['principal']
+  readonly requiredRight?: UpgradeContext['requiredRight']
+  readonly activeSessionCount?: number
+  readonly remoteAddrHash?: string
+}
+
+export interface ReattachArgs extends UpgradeArgs {
+  readonly sessionId: string
+}
+
+export interface HandshakeOpts {
+  readonly host?: HostFixture
+  readonly now?: number
+  /** MITM: pubkey the client verifies host_hello against (default = the real agentPubkey). */
+  readonly verifyAgainstPubkey?: Uint8Array
+  /** MITM: mutate the host_hello the client receives (tampered transcript / hostEphPub). */
+  readonly tamperHostHello?: (h: HostHello) => HostHello
+}
+
+export interface EstablishedSessions {
+  readonly client: E2ESession
+  readonly host: E2ESession
+  readonly spy: RelaySpy
+  readonly agentPubkey: Uint8Array
+}
+
+export interface RelayWorld {
+  readonly now: number
+  readonly signingKey: CryptoKey
+  readonly publicRaw: Uint8Array
+  readonly hostA: HostFixture
+  readonly hostB: HostFixture
+  readonly allowedOrigins: readonly string[]
+  readonly deps: EnforceDeps
+  readonly audit: AuditFake
+  readonly revocation: RevocationFake
+  readonly buckets: TokenBucketFake
+  readonly bus: RevocationBusFake
+  readonly sessions: MutableSessionRegistry
+  principal(accountId: string, over?: Parameters<typeof principal>[1]): ReturnType<typeof principal>
+  setStepUpPolicy(policy: StepUpPolicy): void
+  issueCap(o: {
+    accountId: string
+    host: string
+    aud: string
+    rights?: readonly UpgradeContext['requiredRight'][]
+    ttl?: number
+    now?: number
+  }): Promise<CapBundle>
+  craftMalformedDpop(o: {
+    accountId: string
+    host: string
+    aud: string
+    now?: number
+    blobLen?: number
+  }): Promise<{ raw: string; dpop: UpgradeContext['dpop'] }>
+  upgrade(a: UpgradeArgs): Promise<AuthzOutcome>
+  reattach(a: ReattachArgs): Promise<AuthzOutcome>
+  addSession(e: { sessionId: string; hostId: string; accountId: string }): void
+  establishSession(opts?: HandshakeOpts): Promise<EstablishedSessions>
+  newReplaySealer(sessionId: string, host?: HostFixture): ReplaySealer
+  /** Browser-side re-derivation + open of a replay frame (throws on AEAD failure / wrong epoch). */
+  openReplay(sessionId: string, epoch: string, env: E2EEnvelope, host?: HostFixture): Uint8Array
+  revokeToken(jti: string, exp?: number): Promise<void>
+  revoke(scope: RevocationScope): Promise<void>
+}
+
+export async function buildRelayWorld(now: number = DEFAULT_NOW): Promise<RelayWorld> {
+  const { signingKey, publicRaw } = await setupP5SigningKey()
+  resetDpopCacheForTest()
+
+  const hostA = await makeHostFixture('alice', 'acct-A')
+  const hostB = await makeHostFixture('bob', 'acct-B')
+
+  const hostRecords: HostRecord[] = [
+    makeHostRecord(hostA.accountId, hostA.hostId),
+    makeHostRecord(hostB.accountId, hostB.hostId),
+  ]
+  const hosts = fakeHostRegistry(hostRecords)
+  const sessions = fakeSessionRegistry([])
+  const revocation = fakeRevocationStore()
+  const buckets = fakeTokenBucket()
+  const audit = fakeAuditSink()
+  const bus = fakeRevocationBus()
+  const allowedOrigins = [hostA.origin, hostB.origin]
+
+  let stepUpPolicy: StepUpPolicy = NO_STEP_UP
+  const deps: EnforceDeps = {
+    hosts,
+    sessions,
+    revocation,
+    buckets,
+    audit,
+    stepUpPolicyFor: () => stepUpPolicy,
+  }
+
+  function ctxFor(a: UpgradeArgs): UpgradeContext {
+    return {
+      capabilityRaw: a.raw,
+      originHeader: a.origin,
+      expectedAud: a.aud,
+      requestedHostId: a.host,
+      requiredRight: a.requiredRight ?? 'attach',
+      remoteAddrHash: a.remoteAddrHash ?? 'ip-hash',
+      activeSessionCount: a.activeSessionCount ?? 0,
+      dpop: a.dpop,
+      principal: a.principal ?? null,
+    }
+  }
+
+  const replayCrypto = { deriveContentKey, sealReplayFrame }
+
+  return {
+    now,
+    signingKey,
+    publicRaw,
+    hostA,
+    hostB,
+    allowedOrigins,
+    deps,
+    audit,
+    revocation,
+    buckets,
+    bus,
+    sessions,
+    principal,
+    setStepUpPolicy(policy) {
+      stepUpPolicy = policy
+    },
+    issueCap(o) {
+      return issueCapBundle(signingKey, {
+        accountId: o.accountId,
+        host: o.host,
+        aud: o.aud,
+        rights: o.rights,
+        ttl: o.ttl,
+        now: o.now ?? now,
+      })
+    },
+    craftMalformedDpop(o) {
+      return craftMalformedDpopBundle(signingKey, {
+        accountId: o.accountId,
+        host: o.host,
+        aud: o.aud,
+        now: o.now ?? now,
+        blobLen: o.blobLen,
+      })
+    },
+    upgrade(a) {
+      return onUpgrade(ctxFor(a), deps, allowedOrigins, a.now)
+    },
+    reattach(a) {
+      return onReattach({ ...ctxFor(a), sessionId: a.sessionId }, deps, allowedOrigins, a.now)
+    },
+    addSession(e) {
+      sessions.add(e)
+    },
+    async establishSession(opts: HandshakeOpts = {}): Promise<EstablishedSessions> {
+      const h = opts.host ?? hostA
+      const hsNow = opts.now ?? now
+      const client = createClientHandshake({
+        aeadOffer: ['xchacha20-poly1305', 'aes-256-gcm'],
+        deviceAuthProofProvider: {
+          proofFor: (_hostId, binding) =>
+            signDeviceAuthProof(principal(h.accountId), binding, signingKey, hsNow),
+        },
+        verifier: {
+          verify: async (pub, transcript, sig) =>
+            verifyEd25519(await importEd25519PublicRaw(pub), sig, transcript),
+        },
+        pinStore: new MemoryDevicePinStore(),
+        hostId: h.hostId,
+      })
+      const host = createHostHandshake({
+        signer: { sign: (transcript) => signEd25519(h.signingPriv, transcript) },
+        agentPubkey: h.agentPubkey,
+        supported: ['xchacha20-poly1305', 'aes-256-gcm'],
+        verifyDeviceProof: (proof, binding) => verifyDeviceProof(proof, binding, hsNow),
+      })
+      const clientHello = await client.start()
+      const rawHostHello = await host.onClientHello(clientHello)
+      const hostHello = opts.tamperHostHello ? opts.tamperHostHello(rawHostHello) : rawHostHello
+      const clientResult = await client.onHostHello(
+        hostHello,
+        opts.verifyAgainstPubkey ?? h.agentPubkey,
+      )
+      return {
+        client: createE2ESession('client', clientResult),
+        host: createE2ESession('host', host.result!),
+        spy: new RelaySpy(),
+        agentPubkey: h.agentPubkey,
+      }
+    },
+    newReplaySealer(sessionId, host = hostA) {
+      return createReplaySealer(host.hostContentSecret, sessionId, host.replayAlg, replayCrypto)
+    },
+    openReplay(sessionId, epoch, env, host = hostA) {
+      const key = deriveContentKey({
+        hostContentSecret: host.hostContentSecret,
+        sessionId,
+        alg: host.replayAlg,
+        epoch,
+      })
+      return openReplayCiphertext(key, encodeEnvelope(env))
+    },
+    async revokeToken(jti, exp = now + 60) {
+      await revokeToken(jti, exp, revocation)
+    },
+    async revoke(scope) {
+      await revoke(scope, revocation, hosts, bus, now)
+    },
+  }
+}
diff --git a/e2e/package.json b/e2e/package.json
new file mode 100644
index 0000000..4aada21
--- /dev/null
+++ b/e2e/package.json
@@ -0,0 +1,12 @@
+{
+  "name": "relay-e2e-suite",
+  "version": "0.0.0",
+  "private": true,
+  "type": "module",
+  "description": "Cross-package end-to-end + adversarial security test harness for the rendezvous-relay service. Wires the REAL P1/P2/P4/P5/P6 exports through in-memory seams and an untrusted-relay attacker vantage; dynamically re-validates the audit findings F1-F6 plus MITM/replay/reflect/INV2/cross-tenant.",
+  "scripts": {
+    "test": "vitest run",
+    "test:watch": "vitest",
+    "typecheck": "tsc --noEmit"
+  }
+}
diff --git a/e2e/tests/adversarial-auth.test.ts b/e2e/tests/adversarial-auth.test.ts
new file mode 100644
index 0000000..58bd275
--- /dev/null
+++ b/e2e/tests/adversarial-auth.test.ts
@@ -0,0 +1,226 @@
+/**
+ * Auth (P5) attack matrix — dynamically re-validates the confirmed findings F1–F4 plus cross-tenant
+ * isolation and capability single-use. Each case ASSERTS the defense holds through the REAL
+ * relay-auth enforcement path. Pass an explicit `now` everywhere.
+ */
+import { describe, it, expect, beforeEach } from 'vitest'
+import {
+  needsStepUp,
+  recordStepUp,
+  verifyCapabilityToken,
+  verifyDpopProof,
+  finishAuthentication,
+  WebAuthnError,
+  type WebAuthnVerifier,
+  type AuthenticationResponse,
+  type WebAuthnCredential,
+} from 'relay-auth'
+import {
+  buildRelayWorld,
+  DEFAULT_NOW,
+  STRICT_PASSKEY,
+  NO_STEP_UP,
+  type RelayWorld,
+} from '../harness/world.js'
+
+const NOW = DEFAULT_NOW
+
+describe('adversarial — auth (P5)', () => {
+  let world: RelayWorld
+  beforeEach(async () => {
+    world = await buildRelayWorld(NOW)
+  })
+
+  // ── F2 · mandatory step-up is fail-closed on the new-session path ──────────────────────────────
+  describe('F2 (dynamic): host-driven step-up gate is fail-closed', () => {
+    it('STRICT policy + principal:null → DENIED 403 step_up_required', async () => {
+      const { hostA } = world
+      world.setStepUpPolicy(STRICT_PASSKEY)
+      const cap = await world.issueCap({ accountId: hostA.accountId, host: hostA.hostId, aud: hostA.aud })
+      const out = await world.upgrade({
+        raw: cap.raw,
+        dpop: cap.dpop,
+        host: hostA.hostId,
+        aud: hostA.aud,
+        origin: hostA.origin,
+        principal: null,
+        now: NOW,
+      })
+      expect(out).toMatchObject({ ok: false, status: 403, reason: 'step_up_required' })
+      expect(world.audit.events.some((e) => e.action === 'stepup' && e.outcome === 'deny')).toBe(true)
+    })
+
+    it('required:false policy + principal:null → allowed (non-step-up host preserved)', async () => {
+      const { hostA } = world
+      world.setStepUpPolicy(NO_STEP_UP)
+      const cap = await world.issueCap({ accountId: hostA.accountId, host: hostA.hostId, aud: hostA.aud })
+      const out = await world.upgrade({
+        raw: cap.raw,
+        dpop: cap.dpop,
+        host: hostA.hostId,
+        aud: hostA.aud,
+        origin: hostA.origin,
+        principal: null,
+        now: NOW,
+      })
+      expect(out.ok).toBe(true)
+    })
+  })
+
+  // ── F1 · step-up factor must be method-bound (a passkey requirement ≠ a TOTP step-up) ───────────
+  describe('F1 (dynamic): step-up freshness is bound to the required method', () => {
+    it('a fresh TOTP step-up does NOT satisfy a STRICT passkey policy; a passkey step-up DOES', async () => {
+      const { hostA } = world
+      world.setStepUpPolicy(STRICT_PASSKEY)
+
+      const totp = recordStepUp(world.principal('acct-A', { authAt: NOW }), 'totp', NOW)
+      expect(needsStepUp(totp, STRICT_PASSKEY, NOW)).toBe(true)
+      const capT = await world.issueCap({ accountId: hostA.accountId, host: hostA.hostId, aud: hostA.aud })
+      const deniedTotp = await world.upgrade({
+        raw: capT.raw,
+        dpop: capT.dpop,
+        host: hostA.hostId,
+        aud: hostA.aud,
+        origin: hostA.origin,
+        principal: totp,
+        now: NOW,
+      })
+      expect(deniedTotp).toMatchObject({ ok: false, status: 403, reason: 'step_up_required' })
+
+      const passkey = recordStepUp(world.principal('acct-A', { authAt: NOW }), 'passkey', NOW)
+      expect(needsStepUp(passkey, STRICT_PASSKEY, NOW)).toBe(false)
+      const capP = await world.issueCap({ accountId: hostA.accountId, host: hostA.hostId, aud: hostA.aud })
+      const allowedPasskey = await world.upgrade({
+        raw: capP.raw,
+        dpop: capP.dpop,
+        host: hostA.hostId,
+        aud: hostA.aud,
+        origin: hostA.origin,
+        principal: passkey,
+        now: NOW,
+      })
+      expect(allowedPasskey.ok).toBe(true)
+    })
+  })
+
+  // ── F4 · a thumbprint-matching but malformed DPoP key must fail-safe (resolve false, never throw) ─
+  describe('F4 (dynamic): verifyDpopProof is totally fail-safe', () => {
+    it('a proof whose jwk.x is a non-32-byte blob RESOLVES false and yields a clean denied outcome', async () => {
+      const { hostA } = world
+      const craft = await world.craftMalformedDpop({
+        accountId: hostA.accountId,
+        host: hostA.hostId,
+        aud: hostA.aud,
+      })
+
+      // Direct: the verifier resolves to false — it never throws / rejects (audit-evasion + DoS fix).
+      const tok = await verifyCapabilityToken(craft.raw, hostA.aud, NOW)
+      await expect(verifyDpopProof(tok, craft.dpop, NOW)).resolves.toBe(false)
+
+      // Via the full enforcement path: a clean denied AuthzOutcome, not an exception.
+      const out = await world.upgrade({
+        raw: craft.raw,
+        dpop: craft.dpop,
+        host: hostA.hostId,
+        aud: hostA.aud,
+        origin: hostA.origin,
+        now: NOW,
+      })
+      expect(out).toMatchObject({ ok: false, reason: 'dpop_proof_failed' })
+      // Exactly one audited deny was emitted (no unhandled rejection, no audit evasion).
+      expect(world.audit.events.some((e) => e.outcome === 'deny')).toBe(true)
+    })
+  })
+
+  // ── F3 · WebAuthn assertion must be bound to the stored credential id ───────────────────────────
+  describe('F3: an assertion whose credentialId ≠ the stored credential is rejected', () => {
+    const RP_ID = 'alice.term.example.com'
+    const ORIGIN = 'https://alice.term.example.com'
+    const cred: WebAuthnCredential = {
+      credentialId: 'cred-1',
+      accountId: 'acct-A',
+      publicKey: new Uint8Array([1, 2, 3]),
+      signCount: 5,
+      transports: ['internal'],
+      createdAt: '2026-01-01T00:00:00.000Z',
+    }
+    // A permissive verifier that would "verify" ANY assertion — the credentialId cross-check must
+    // still reject before the verifier's verdict is trusted.
+    const forgivingVerifier: WebAuthnVerifier = {
+      verifyRegistration: async () => ({
+        verified: true,
+        credentialId: 'cred-1',
+        publicKey: new Uint8Array([1, 2, 3]),
+        signCount: 0,
+        transports: ['internal'],
+      }),
+      verifyAuthentication: async (_r, _c, _rp, _o, _pk, _cid, stored) => ({
+        verified: true,
+        newSignCount: stored + 1,
+      }),
+    }
+
+    it('rejects with WebAuthnError even though the mock verifier returns verified:true', async () => {
+      const resp: AuthenticationResponse = {
+        clientChallenge: 'chal',
+        origin: ORIGIN,
+        rpId: RP_ID,
+        credentialId: 'other-cred', // ≠ cred.credentialId
+      }
+      await expect(
+        finishAuthentication(cred, resp, 'chal', RP_ID, ORIGIN, forgivingVerifier, NOW),
+      ).rejects.toBeInstanceOf(WebAuthnError)
+      await expect(
+        finishAuthentication(cred, resp, 'chal', RP_ID, ORIGIN, forgivingVerifier, NOW),
+      ).rejects.toThrow('credential id mismatch')
+    })
+  })
+
+  // ── Cross-tenant · a token for account A can never reach a host owned by account B ──────────────
+  describe('cross-tenant isolation (INV1)', () => {
+    it('an A-account token presented at host B (owned by B) is DENIED 403', async () => {
+      const { hostA, hostB } = world
+      // token.host === requestedHostId (hostB) so host-scope passes; the registry then shows hostB
+      // belongs to acct-B ≠ token.sub (acct-A) → the cross_tenant gate fires.
+      const cap = await world.issueCap({ accountId: hostA.accountId, host: hostB.hostId, aud: hostB.aud })
+      const out = await world.upgrade({
+        raw: cap.raw,
+        dpop: cap.dpop,
+        host: hostB.hostId,
+        aud: hostB.aud,
+        origin: hostB.origin,
+        now: NOW,
+      })
+      expect(out).toMatchObject({ ok: false, status: 403 })
+      if (!out.ok) expect(['cross_tenant', 'host_scope_mismatch']).toContain(out.reason)
+      expect(world.audit.events.some((e) => e.action === 'cross-tenant-attempt' && e.outcome === 'deny')).toBe(true)
+    })
+  })
+
+  // ── Capability single-use · a token+jti may be upgraded exactly once ────────────────────────────
+  describe('capability single-use (consumeOnce)', () => {
+    it('the same token+jti upgraded twice → the second is denied token_replayed', async () => {
+      const { hostA } = world
+      const cap = await world.issueCap({ accountId: hostA.accountId, host: hostA.hostId, aud: hostA.aud })
+      const first = await world.upgrade({
+        raw: cap.raw,
+        dpop: cap.dpop,
+        host: hostA.hostId,
+        aud: hostA.aud,
+        origin: hostA.origin,
+        now: NOW,
+      })
+      expect(first.ok).toBe(true)
+
+      const second = await world.upgrade({
+        raw: cap.raw,
+        dpop: await cap.newDpop(NOW), // fresh DPoP so the jti burn (not the DPoP cache) is what denies
+        host: hostA.hostId,
+        aud: hostA.aud,
+        origin: hostA.origin,
+        now: NOW,
+      })
+      expect(second).toMatchObject({ ok: false, status: 403, reason: 'token_replayed' })
+    })
+  })
+})
diff --git a/e2e/tests/adversarial-transport.test.ts b/e2e/tests/adversarial-transport.test.ts
new file mode 100644
index 0000000..08afaae
--- /dev/null
+++ b/e2e/tests/adversarial-transport.test.ts
@@ -0,0 +1,115 @@
+/**
+ * Transport (P4) attack matrix, run from the untrusted-relay / attacker vantage (the RelaySpy).
+ * Each case ASSERTS the defense holds. Wires the REAL relay-e2e handshake/session + agent replay
+ * sealer through the harness. Pass an explicit `now` everywhere.
+ */
+import { describe, it, expect, beforeEach } from 'vitest'
+import { FingerprintMismatchError } from 'relay-e2e'
+import { buildRelayWorld, DEFAULT_NOW, type RelayWorld } from '../harness/world.js'
+
+const utf8 = (s: string): Uint8Array => new TextEncoder().encode(s)
+const fromUtf8 = (b: Uint8Array): string => new TextDecoder().decode(b)
+const NOW = DEFAULT_NOW
+
+function flipByte(b: Uint8Array, i = 0): Uint8Array {
+  const c = b.slice()
+  c[i] = (c[i]! ^ 0xff) & 0xff
+  return c
+}
+
+describe('adversarial — transport (P4)', () => {
+  let world: RelayWorld
+  beforeEach(async () => {
+    world = await buildRelayWorld(NOW)
+  })
+
+  describe('MITM: host_hello must verify against the registry key', () => {
+    it('rejects when the client verifies host_hello against a WRONG agentPubkey (no keys derived)', async () => {
+      // The malicious relay swaps in a key it controls; the client checks against hostB's real key.
+      await expect(
+        world.establishSession({ verifyAgainstPubkey: world.hostB.agentPubkey }),
+      ).rejects.toBeInstanceOf(FingerprintMismatchError)
+    })
+
+    it('rejects a tampered host_hello (flipped hostEphPub breaks the transcript signature)', async () => {
+      await expect(
+        world.establishSession({
+          tamperHostHello: (h) => ({ ...h, hostEphPub: flipByte(h.hostEphPub) }),
+        }),
+      ).rejects.toBeInstanceOf(FingerprintMismatchError)
+    })
+  })
+
+  it('reflection: a c2h frame fed back into the client’s own open is rejected (direction split)', async () => {
+    const { client } = await world.establishSession()
+    const c2h = client.seal(utf8('sudo rm -rf /'))
+    // Reflecting the client's own ciphertext back to it must fail: the client opens with the h2c
+    // read key + h2c aad label, so the tag over the c2h direction never verifies.
+    expect(() => client.open(c2h)).toThrow()
+  })
+
+  it('replay: delivering the same valid frame twice → the second open throws (SequenceGuard)', async () => {
+    const { client, host, spy } = await world.establishSession()
+    const f0 = spy.forward(client.seal(utf8('whoami')))
+    expect(fromUtf8(host.open(f0))).toBe('whoami')
+    expect(() => host.open(f0)).toThrow() // seq 0 already consumed → strict-successor guard
+  })
+
+  it('reorder: delivering seq 1 before seq 0 → open throws (strict successor)', async () => {
+    const { client, host } = await world.establishSession()
+    const f0 = client.seal(utf8('cmd-0'))
+    const f1 = client.seal(utf8('cmd-1'))
+    expect(() => host.open(f1)).toThrow() // expected seq 0, got 1
+    // and the in-order pair still works on a fresh pair (sanity)
+    expect(fromUtf8(host.open(f0))).toBe('cmd-0')
+    expect(fromUtf8(host.open(f1))).toBe('cmd-1')
+  })
+
+  it('INV2: the RelaySpy ciphertext never contains the plaintext marker', async () => {
+    const { client, host, spy } = await world.establishSession()
+    const marker = `TOP_SECRET_${crypto.randomUUID()}`
+    for (let i = 0; i < 3; i++) {
+      const wire = spy.forward(client.seal(utf8(`${marker}#${i}`)))
+      expect(fromUtf8(host.open(wire))).toBe(`${marker}#${i}`)
+    }
+    expect(spy.contains(marker)).toBe(false)
+    expect(spy.captured.length).toBe(3)
+  })
+
+  describe('F6 (dynamic): recoverable K_content must not reuse (key, nonce) across sealer generations', () => {
+    it('two generations for the same (secret, sessionId) get different epochs → different keys at seq 0', () => {
+      const sessionId = 'sess-restart-1'
+      const gen1 = world.newReplaySealer(sessionId)
+      const gen2 = world.newReplaySealer(sessionId) // simulates an agent restart / re-attach
+
+      expect(gen2.epoch).not.toBe(gen1.epoch)
+
+      const pt = utf8('IDENTICAL PLAINTEXT AT SEQ 0')
+      const e1 = gen1.seal(pt)
+      const e2 = gen2.seal(pt)
+
+      // Same deterministic nonce (seq 0) …
+      expect(e1.seq).toBe(0n)
+      expect(e2.seq).toBe(0n)
+      expect(Buffer.from(e1.nonce).equals(Buffer.from(e2.nonce))).toBe(true)
+      // … yet a FRESH key per generation ⇒ ciphertext + tag differ (no (key, nonce) reuse).
+      expect(Buffer.from(e1.ciphertext).equals(Buffer.from(e2.ciphertext))).toBe(false)
+      expect(Buffer.from(e1.tag).equals(Buffer.from(e2.tag))).toBe(false)
+
+      // Cross-generation open fails: gen1's epoch-derived key cannot open gen2's frame.
+      expect(() => world.openReplay(sessionId, gen1.epoch, e2)).toThrow()
+
+      // Recoverability WITHIN a generation is preserved (same epoch ⇒ same key).
+      expect(fromUtf8(world.openReplay(sessionId, gen1.epoch, e1))).toBe('IDENTICAL PLAINTEXT AT SEQ 0')
+      expect(fromUtf8(world.openReplay(sessionId, gen2.epoch, e2))).toBe('IDENTICAL PLAINTEXT AT SEQ 0')
+    })
+
+    it('the replay ciphertext itself never contains the plaintext marker (INV2 on the replay path)', () => {
+      const sealer = world.newReplaySealer('sess-inv2')
+      const marker = 'REPLAY_MARKER_ABC'
+      const env = sealer.seal(utf8(marker))
+      expect(Buffer.from(env.ciphertext).toString('latin1')).not.toContain(marker)
+      expect(Buffer.from(env.ciphertext).toString('utf8')).not.toContain(marker)
+    })
+  })
+})
diff --git a/e2e/tests/flow.test.ts b/e2e/tests/flow.test.ts
new file mode 100644
index 0000000..5bcbe0d
--- /dev/null
+++ b/e2e/tests/flow.test.ts
@@ -0,0 +1,99 @@
+/**
+ * Happy-path full flow, end-to-end across P5 (auth) + P4 (E2E crypto) + P2 (replay), asserting each
+ * stage. Everything runs through the REAL package exports; only registries/buckets/sockets are faked.
+ */
+import { describe, it, expect, beforeEach } from 'vitest'
+import { buildRelayWorld, DEFAULT_NOW, type RelayWorld } from '../harness/world.js'
+
+const utf8 = (s: string): Uint8Array => new TextEncoder().encode(s)
+const fromUtf8 = (b: Uint8Array): string => new TextDecoder().decode(b)
+const NOW = DEFAULT_NOW
+
+describe('relay flow (happy path)', () => {
+  let world: RelayWorld
+  beforeEach(async () => {
+    world = await buildRelayWorld(NOW)
+  })
+
+  it('issueCap → upgrade allows (origin ok, DPoP bound, deny-by-default satisfied)', async () => {
+    const { hostA } = world
+    const cap = await world.issueCap({ accountId: hostA.accountId, host: hostA.hostId, aud: hostA.aud })
+    const out = await world.upgrade({
+      raw: cap.raw,
+      dpop: cap.dpop,
+      host: hostA.hostId,
+      aud: hostA.aud,
+      origin: hostA.origin,
+      now: NOW,
+    })
+    expect(out.ok).toBe(true)
+    expect(world.audit.events.at(-1)).toMatchObject({ outcome: 'allow', action: 'attach' })
+  })
+
+  it('handshake establishes MATCHING session keys on both sides (client↔host round-trip)', async () => {
+    const { client, host } = await world.establishSession()
+    // Matching keys ⇒ bidirectional plaintext round-trips through the direction split.
+    const c2h = host.open(client.seal(utf8('ls -la')))
+    expect(fromUtf8(c2h)).toBe('ls -la')
+    const h2c = client.open(host.seal(utf8('total 0')))
+    expect(fromUtf8(h2c)).toBe('total 0')
+  })
+
+  it('seals client→host and host→client through the RelaySpy; the RelaySpy never sees plaintext (INV2)', async () => {
+    const { client, host, spy } = await world.establishSession()
+    const marker = `PLAINTEXT_${crypto.randomUUID()}`
+
+    const up = spy.forward(client.seal(utf8(marker)))
+    expect(fromUtf8(host.open(up))).toBe(marker)
+    const down = spy.forward(host.seal(utf8(`reply_${marker}`)))
+    expect(fromUtf8(client.open(down))).toBe(`reply_${marker}`)
+
+    expect(spy.contains(marker)).toBe(false)
+    expect(spy.captured.length).toBe(2)
+  })
+
+  it('reattach to an own-account session is allowed', async () => {
+    const { hostA } = world
+    const sessionId = crypto.randomUUID()
+    world.addSession({ sessionId, hostId: hostA.hostId, accountId: hostA.accountId })
+    const cap = await world.issueCap({ accountId: hostA.accountId, host: hostA.hostId, aud: hostA.aud })
+    const out = await world.reattach({
+      raw: cap.raw,
+      dpop: cap.dpop,
+      host: hostA.hostId,
+      aud: hostA.aud,
+      origin: hostA.origin,
+      sessionId,
+      now: NOW,
+    })
+    expect(out.ok).toBe(true)
+    expect(world.audit.events.at(-1)).toMatchObject({ outcome: 'allow', action: 'reattach' })
+  })
+
+  it('revokeToken then re-presenting the same jti (fresh DPoP) is denied', async () => {
+    const { hostA } = world
+    const cap = await world.issueCap({ accountId: hostA.accountId, host: hostA.hostId, aud: hostA.aud })
+    const first = await world.upgrade({
+      raw: cap.raw,
+      dpop: cap.dpop,
+      host: hostA.hostId,
+      aud: hostA.aud,
+      origin: hostA.origin,
+      now: NOW,
+    })
+    expect(first.ok).toBe(true)
+    if (!first.ok) return
+
+    await world.revokeToken(first.jti)
+
+    const second = await world.upgrade({
+      raw: cap.raw,
+      dpop: await cap.newDpop(NOW), // fresh DPoP jti so we reach the revocation gate, not the DPoP cache
+      host: hostA.hostId,
+      aud: hostA.aud,
+      origin: hostA.origin,
+      now: NOW,
+    })
+    expect(second).toMatchObject({ ok: false, status: 403, reason: 'token_revoked' })
+  })
+})
diff --git a/e2e/tests/smoke.test.ts b/e2e/tests/smoke.test.ts
new file mode 100644
index 0000000..9c20b4f
--- /dev/null
+++ b/e2e/tests/smoke.test.ts
@@ -0,0 +1,21 @@
+import { describe, it, expect } from 'vitest'
+// Cross-package resolution smoke test: prove the harness can bare-import the REAL exports of
+// every relay package (each resolves via its own node_modules/relay-contracts symlink transitively).
+import { issueCapabilityToken, onUpgrade, needsStepUp } from 'relay-auth'
+import { createClientHandshake, createHostHandshake, createE2ESession, deriveContentKey } from 'relay-e2e'
+import { createReplaySealer } from 'agent'
+import { CapabilityTokenSchema } from 'relay-contracts'
+
+describe('cross-package import smoke', () => {
+  it('resolves the real exports of relay-auth / relay-e2e / agent / relay-contracts', () => {
+    expect(typeof issueCapabilityToken).toBe('function')
+    expect(typeof onUpgrade).toBe('function')
+    expect(typeof needsStepUp).toBe('function')
+    expect(typeof createClientHandshake).toBe('function')
+    expect(typeof createHostHandshake).toBe('function')
+    expect(typeof createE2ESession).toBe('function')
+    expect(typeof deriveContentKey).toBe('function')
+    expect(typeof createReplaySealer).toBe('function')
+    expect(CapabilityTokenSchema).toBeDefined()
+  })
+})
diff --git a/e2e/tsconfig.json b/e2e/tsconfig.json
new file mode 100644
index 0000000..48130c7
--- /dev/null
+++ b/e2e/tsconfig.json
@@ -0,0 +1,15 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "NodeNext",
+    "moduleResolution": "NodeNext",
+    "lib": ["ES2022", "DOM"],
+    "strict": true,
+    "noEmit": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "allowImportingTsExtensions": true,
+    "types": ["node"]
+  },
+  "include": ["harness/**/*.ts", "tests/**/*.ts"]
+}
diff --git a/e2e/vitest.config.ts b/e2e/vitest.config.ts
new file mode 100644
index 0000000..b31aa2a
--- /dev/null
+++ b/e2e/vitest.config.ts
@@ -0,0 +1,8 @@
+import { defineConfig } from 'vitest/config'
+
+export default defineConfig({
+  test: {
+    include: ['tests/**/*.test.ts'],
+    environment: 'node',
+  },
+})