diff --git a/.changeset/passkey-enrollment-access-identity.md b/.changeset/passkey-enrollment-access-identity.md
new file mode 100644
index 0000000..e8f428e
--- /dev/null
+++ b/.changeset/passkey-enrollment-access-identity.md
@@ -0,0 +1,39 @@
+---
+'@seamless-auth/core': minor
+'@seamless-auth/express': minor
+'@seamless-auth/fastify': minor
+---
+
+Passkey enrollment now forwards the access session. This is a coordinated contract
+change with `seamless-auth-api`, which refuses a pre-auth token on these routes as of the
+matching release.
+
+`/webAuthn/register/start` and `/webAuthn/register/finish` read the registration cookie
+and sent the ephemeral token upstream. The auth API mints one of those for an account
+that already exists, from an email address alone, so anyone who knew an address could
+enroll a credential against the account and sign in as its owner. Both routes now read
+the access cookie and forward the access token. `/webAuthn/login/start` and
+`/webAuthn/login/finish` are unchanged and still take the pre-auth cookie, because
+authenticating is what they are for.
+
+No shipped flow loses a step. Registration proves an address with an email OTP, and
+verifying it issues a session, so the client holds an access cookie by the time it offers
+a passkey. An application that offered enrollment before verifying an address has to move
+that step after it.
+
+Upgrade this and the auth API together. There is no safe order between them: an older
+adapter sends the token the new API refuses, and this release sends one an older API
+refuses, so enrollment answers `401` until both sides land.
+
+`finishRegisterHandler` no longer issues session cookies. Enrolling a passkey is not a
+sign-in, and the caller now arrives holding a session, so minting a second one left the
+first live and unrevoked while counting against the API's concurrent session limit, which
+can evict the user's other devices. The route still answers `204`.
+
+`FinishRegisterOptions` drops `audience`, `cookieDomain`, `accessCookieName` and
+`refreshCookieName`, and `FinishRegisterResult` drops `setCookies`. Only the two adapters
+in this workspace passed them, and both are updated. Code calling
+`finishRegisterHandler` directly should pass `{ authServerUrl }` alone.
+
+This does not change the pre-auth routes' silent refresh, which still mints an access
+token into a cookie those routes cannot use. That is tracked separately.
diff --git a/packages/core/src/ensureCookies.ts b/packages/core/src/ensureCookies.ts
index 56f227e..245ebdc 100644
--- a/packages/core/src/ensureCookies.ts
+++ b/packages/core/src/ensureCookies.ts
@@ -60,12 +60,18 @@ const COOKIE_REQUIREMENTS: Record<
 > = {
   "/webAuthn/login/finish": { name: "preAuthCookieName", required: true },
   "/webAuthn/login/start": { name: "preAuthCookieName", required: true },
+  // Enrollment takes the access cookie, not the registration one. The auth
+  // API refuses an ephemeral token here: it mints one for an account that
+  // already exists from an email address alone, so accepting it let anyone
+  // who knew an address enroll a credential and take the account over.
+  // Signup reaches this point holding a session already, because verifying
+  // the email OTP issues one.
   "/webAuthn/register/start": {
-    name: "registrationCookieName",
+    name: "accessCookieName",
     required: true,
   },
   "/webAuthn/register/finish": {
-    name: "registrationCookieName",
+    name: "accessCookieName",
     required: true,
   },
   "/otp/verify-email-otp": {
diff --git a/packages/core/src/handlers/finishRegister.ts b/packages/core/src/handlers/finishRegister.ts
index 83c653b..a3c8178 100644
--- a/packages/core/src/handlers/finishRegister.ts
+++ b/packages/core/src/handlers/finishRegister.ts
@@ -1,8 +1,6 @@
 import { authFetch } from "../authFetch.js";
-import { issueSessionCookies } from "../upstreamSession.js";
 import { readPassthroughFailure } from "../upstreamError.js";
 import type { ResultFailure } from "../result.js";
-import type { CookiePayload } from "../ensureCookies.js";
 
 export interface FinishRegisterInput {
   authorization?: string;
@@ -14,20 +12,10 @@ export interface FinishRegisterInput {
 
 export interface FinishRegisterOptions {
   authServerUrl: string;
-  audience: string;
-  cookieDomain?: string;
-  accessCookieName: string;
-  refreshCookieName: string;
 }
 
 export interface FinishRegisterResult extends ResultFailure {
   status: number;
-  setCookies?: {
-    name: string;
-    value: CookiePayload;
-    ttl: number;
-    domain?: string;
-  }[];
 }
 
 export async function finishRegisterHandler(
@@ -52,14 +40,10 @@ export async function finishRegisterHandler(
     };
   }
 
-  return {
-    status: 204,
-    setCookies: await issueSessionCookies(data, {
-      authServerUrl: opts.authServerUrl,
-      audience: opts.audience,
-      accessCookieName: opts.accessCookieName,
-      refreshCookieName: opts.refreshCookieName,
-      cookieDomain: opts.cookieDomain,
-    }),
-  };
+  // Enrolling a passkey is not a sign-in. This route takes the access cookie,
+  // so the caller already holds a session, and issuing a second one left the
+  // first live and unrevoked while counting against the API's concurrent
+  // session limit, which can evict the user's other devices. The auth API
+  // stopped returning tokens here for the same reason.
+  return { status: 204 };
 }
diff --git a/packages/express/src/createServer.ts b/packages/express/src/createServer.ts
index 349d1d5..a8c85e1 100644
--- a/packages/express/src/createServer.ts
+++ b/packages/express/src/createServer.ts
@@ -307,7 +307,7 @@ export function createSeamlessAuthServer(
 
   r.get(
     "/webAuthn/register/start",
-    proxyWithIdentity("webAuthn/register/start", "preAuth", "GET"),
+    proxyWithIdentity("webAuthn/register/start", "access", "GET"),
   );
   r.post("/webAuthn/register/finish", (req, res) =>
     finishRegister(req, res, resolvedOpts),
diff --git a/packages/express/src/handlers/finishRegister.ts b/packages/express/src/handlers/finishRegister.ts
index 9212304..fb9e751 100644
--- a/packages/express/src/handlers/finishRegister.ts
+++ b/packages/express/src/handlers/finishRegister.ts
@@ -22,13 +22,7 @@ export async function finishRegister(
       serviceAuthorization: buildProxyServiceAuthorization(opts),
       forwardedClientIp: buildForwardedClientIp(req, opts.resolveClientIp),
     },
-    {
-      authServerUrl: opts.authServerUrl,
-      audience: opts.audience,
-      cookieDomain: opts.cookieDomain,
-      accessCookieName: opts.accessCookieName!,
-      refreshCookieName: opts.refreshCookieName!,
-    },
+    { authServerUrl: opts.authServerUrl },
   );
 
   respond(res, { ...result, body: { message: "success" } }, opts);
diff --git a/packages/express/tests/stepUpProxy.test.js b/packages/express/tests/stepUpProxy.test.js
index 4d7a00a..2c6a5ac 100644
--- a/packages/express/tests/stepUpProxy.test.js
+++ b/packages/express/tests/stepUpProxy.test.js
@@ -189,14 +189,39 @@ describe("step-up proxy routes", () => {
     const res = await request(createApp())
       .get("/auth/webAuthn/register/start")
       .query({ requirePrf: "true" })
-      .set("Cookie", createRegistrationCookie());
+      .set("Cookie", createAccessCookie());
 
     expect(res.status).toBe(200);
     expect(global.fetch).toHaveBeenCalledWith(
       "https://auth.example.com/webAuthn/register/start?requirePrf=true",
       expect.objectContaining({
         method: "GET",
+        headers: expect.objectContaining({
+          Authorization: "Bearer access-token",
+        }),
       }),
     );
   });
+
+  // The auth API refuses an ephemeral token at enrollment: it mints one for
+  // an account that already exists from an email address alone, so forwarding
+  // it would offer anyone who knew an address a credential on that account.
+  it("refuses passkey registration start on a registration cookie", async () => {
+    const res = await request(createApp())
+      .get("/auth/webAuthn/register/start")
+      .set("Cookie", createRegistrationCookie());
+
+    expect(res.status).toBe(401);
+    expect(global.fetch).not.toHaveBeenCalled();
+  });
+
+  it("refuses passkey registration finish on a registration cookie", async () => {
+    const res = await request(createApp())
+      .post("/auth/webAuthn/register/finish")
+      .set("Cookie", createRegistrationCookie())
+      .send({ attestationResponse: {} });
+
+    expect(res.status).toBe(401);
+    expect(global.fetch).not.toHaveBeenCalled();
+  });
 });
diff --git a/packages/fastify/src/routes/authRoutes.ts b/packages/fastify/src/routes/authRoutes.ts
index 13086f5..2cf9927 100644
--- a/packages/fastify/src/routes/authRoutes.ts
+++ b/packages/fastify/src/routes/authRoutes.ts
@@ -120,7 +120,7 @@ export function registerAuthRoutes(
         serviceAuthorization: buildProxyServiceAuthorization(opts),
         forwardedClientIp: buildForwardedClientIp(req, opts.resolveClientIp),
       },
-      { authServerUrl: opts.authServerUrl, ...sessionCookies },
+      { authServerUrl: opts.authServerUrl },
     );
 
     respond(reply, { ...result, body: { message: "success" } }, opts);
diff --git a/packages/fastify/src/routes/proxyRoutes.ts b/packages/fastify/src/routes/proxyRoutes.ts
index fd5048b..d3e278d 100644
--- a/packages/fastify/src/routes/proxyRoutes.ts
+++ b/packages/fastify/src/routes/proxyRoutes.ts
@@ -30,7 +30,7 @@ export const PROXY_ROUTES: ProxyRouteDefinition[] = [
     method: "GET",
     path: "/webAuthn/register/start",
     upstream: "webAuthn/register/start",
-    identity: "preAuth",
+    identity: "access",
   },
 
   {
diff --git a/packages/fastify/tests/parity.test.js b/packages/fastify/tests/parity.test.js
index 8714e15..2b835f1 100644
--- a/packages/fastify/tests/parity.test.js
+++ b/packages/fastify/tests/parity.test.js
@@ -252,6 +252,28 @@ describe("fastify and express adapters agree", () => {
       { method: "get", path: "/system-config/public" },
       upstream(503, { error: "upstream_unavailable" }),
     ],
+    [
+      "passkey enrollment start on an access session",
+      {
+        method: "get",
+        path: "/webAuthn/register/start",
+        cookie: accessCookie(),
+      },
+      upstream(200, { challenge: "challenge" }),
+    ],
+    // Enrollment moved off the pre-auth cookie because the auth API mints
+    // one for an account that already exists from an email address alone.
+    // Both adapters have to refuse it, or the one that does not hands the
+    // account over.
+    [
+      "passkey enrollment start refuses a pre-auth session",
+      {
+        method: "get",
+        path: "/webAuthn/register/start",
+        cookie: preAuthCookie(),
+      },
+      upstream(200, { challenge: "challenge" }),
+    ],
   ])("%s", async (_label, scenario, upstreamResponse) => {
     const { fastify, express: expressResult } = await bothAdapters(
       scenario,
@@ -268,12 +290,27 @@ describe("fastify and express adapters agree", () => {
   // itself is the contract a consumer reads to tell "sign in again" from "that
   // request was not understood", so it is pinned here by value.
   it.each([
-    ["access-gated", { method: "get", path: "/organizations" }],
     [
-      "pre-auth gated",
+      "an access-gated route with no session",
+      { method: "get", path: "/organizations" },
+    ],
+    [
+      "a pre-auth gated route with no session",
       { method: "post", path: "/webAuthn/login/start", payload: {} },
     ],
-  ])("answers 401 on a %s route with no session, and asks upstream nothing", async (
+    [
+      "an enrollment route with no session",
+      { method: "get", path: "/webAuthn/register/start" },
+    ],
+    [
+      "an enrollment route holding only a pre-auth session",
+      {
+        method: "get",
+        path: "/webAuthn/register/start",
+        cookie: preAuthCookie(),
+      },
+    ],
+  ])("answers 401 on %s, and asks upstream nothing", async (
     _label,
     scenario,
   ) => {