fix(tunnel): recover an expired leaf over plain HTTPS, not mTLS

Correction to the previous commit. Its recovery vhost could not work: nginx will not forward an expired client certificate in ANY `ssl_verify_client` mode. `optional` answers a bare `400 The SSL certificate error` before any location runs, and `optional_no_ca` only tolerates CHAIN failures — see nginx's `ngx_ssl_verify_error_optional()`, which covers self-signed / unknown-issuer / unverifiable-leaf and NOT `X509_V_ERR_CERT_HAS_EXPIRED`. Verified live against the deployed :8472 server, which rejected the real expired leaf. So recovery drops mTLS instead of trying to bend it: - agent: `buildTlsOptions` and the mTLS renew transport go back to being strictly fail-closed on expiry — the relaxation is gone from the TLS layer entirely. The rotator now decides per attempt: valid → mTLS `/renew`, expired-inside-grace → plain `/recover`, expired-beyond-grace → terminal `onExhausted` with no request issued at all. - new `recoverCert` POSTs `{cert, csr}` with no client certificate. Possession of the private key is still proven: the CSR is self-signed by it and the host signer already enforces CSR PoP plus `CSR key == registered key`, so a replayed (public) cert without the key yields at most a certificate the attacker cannot authenticate with. - control-plane: `/renew` is strict again (grace 0, matching the terminator). The grace lives on the new `POST /recover`, which reads the cert from the BODY and ignores the `x-client-cert` header, then runs the identical trust pipeline: X.509 path validation to the frp-client-CA anchors, SPIFFE parse, `notBefore` (never graced), registry `active` + account match. Revocation still bites. - deploy: no new vhost, no new SNI, no DNS. One `location = /recover` merged into the existing enroll vhost, documented in `deploy/nginx/enroll-recover-location.md` with the nginx source citation. The load-bearing new test is "a self-signed cert with a FORGED SPIFFE SAN is refused → 401": nginx no longer validates the chain on this path, so that assertion is what keeps `/recover` from being a cert vending machine. Verified: agent 289/289, control-plane 290/290, tsc clean on both.
2026-07-29 09:52:17 +02:00
parent f3f4d8baa6
commit 5509c81eee
13 changed files with 559 additions and 472 deletions
--- a/agent/node_modules
+++ b/agent/node_modules
@@ -0,0 +1 @@
+/Users/yiukai/Documents/git/web-terminal/agent/node_modules
--- a/agent/src/certs/nativeRenew.ts
+++ b/agent/src/certs/nativeRenew.ts
@@ -22,14 +22,13 @@ import type { Keystore } from '../keys/keystore.js'
 import type { Logger } from '../log/logger.js'
 import type { TimerLike } from '../transport/seams.js'
 import { createBackoff } from '../transport/backoff.js'
-import {
-  buildTlsOptions,
-  DEFAULT_EXPIRED_RENEW_GRACE_MS,
-  type CertParser,
-  type TlsClientOptions,
-} from '../transport/dial.js'
+import { buildTlsOptions, type CertParser, type TlsClientOptions } from '../transport/dial.js'
 import { DEFAULT_CERT_RENEW_WINDOW_MS } from '../health/probe.js'
-import { createCertRotator, type CertRotator } from './rotation.js'
+import {
+  createCertRotator,
+  type CertExpiredBeyondGraceError,
+  type CertRotator,
+} from './rotation.js'

 /** Non-secret message from an unknown thrown value (never serializes cert/key material). */
 function errorMessage(err: unknown): string {
@@ -131,7 +130,7 @@ function toHeaderRecord(headers: RequestInit['headers']): Record<string, string>
 */
 export function createMtlsFetch(
  ks: Keystore,
-  opts: { request?: MtlsRequest; certParser?: CertParser; expiredGraceMs?: number } = {},
+  opts: { request?: MtlsRequest; certParser?: CertParser } = {},
 ): typeof fetch {
  const request = opts.request ?? defaultMtlsRequest
  const shim = async (input: Parameters<typeof fetch>[0], init?: RequestInit): Promise<Response> => {
@@ -140,14 +139,9 @@ export function createMtlsFetch(
    // SYSTEM roots — its host (the LE-fronted control-plane) is publicly trusted; pinning the private
    // enroll caChain here fails with "unable to get local issuer certificate". So drop `ca` (absent →
    // node uses the default roots); rejectUnauthorized stays true.
-    // This transport exists ONLY to renew, so it opts into the expired-leaf grace: refusing here is
-    // exactly the deadlock we are fixing (mTLS renew needs the very leaf that lapsed). Past the
-    // window `buildTlsOptions` throws CertExpiredBeyondGraceError, which the rotator treats as
-    // terminal rather than retrying forever.
-    const full = buildTlsOptions(ks, {
-      expiredGraceMs: opts.expiredGraceMs ?? DEFAULT_EXPIRED_RENEW_GRACE_MS,
-      ...(opts.certParser ? { certParser: opts.certParser } : {}),
-    })
+    // Deliberately still fail-closed on an EXPIRED leaf: nginx would refuse to forward it anyway, so
+    // a lapsed leaf is routed to the plain `/recover` endpoint by the rotator instead of through here.
+    const full = buildTlsOptions(ks, { ...(opts.certParser ? { certParser: opts.certParser } : {}) })
    const tls: TlsClientOptions = { cert: full.cert, key: full.key, rejectUnauthorized: full.rejectUnauthorized }
    const reqInit: MtlsRequestInit = {
      method: init?.method ?? 'GET',
@@ -211,7 +205,7 @@ export function wireAutoRenew(
  // at error level, naming the fix — and deliberately do NOT stop the supervisor: `pair` writes fresh
  // cert files that the restart-on-exit frpc child picks up without a manual service restart.
  rotator.onExhausted((err) => {
-    logger.log('error', 'frp-client cert expired beyond renewal grace — run `web-terminal-agent pair <CODE>` to re-pair this host', {
+    logger.log('error', 'frp-client cert expired beyond recovery grace — run `web-terminal-agent pair <CODE>` to re-pair this host', {
      ...meta,
      expiredForMs: err.expiredForMs,
      graceMs: err.graceMs,
@@ -227,8 +221,10 @@ export function wireAutoRenew(
 export interface NativeAutoRenewOpts {
  readonly mtlsRequest?: MtlsRequest
  readonly certParser?: CertParser
-  /** Window in which an already-expired leaf may still authenticate its own renewal. */
+  /** Window in which an already-expired leaf may still be recovered via `/recover`. */
  readonly expiredGraceMs?: number
+  /** Plain (NON-mTLS) fetch for the `/recover` call; unset ⇒ global fetch. */
+  readonly recoverFetchImpl?: typeof fetch
  readonly timer?: TimerLike
  readonly renewBeforeMs?: number
  readonly retryBaseMs?: number
@@ -256,10 +252,11 @@ export function startNativeAutoRenew(
  const fetchImpl = createMtlsFetch(ks, {
    ...(opts.mtlsRequest ? { request: opts.mtlsRequest } : {}),
    ...(opts.certParser ? { certParser: opts.certParser } : {}),
-    ...(opts.expiredGraceMs !== undefined ? { expiredGraceMs: opts.expiredGraceMs } : {}),
  })
  const rotator = createCertRotator(cfg, id, ks, {
    fetchImpl,
+    ...(opts.expiredGraceMs !== undefined ? { expiredGraceMs: opts.expiredGraceMs } : {}),
+    ...(opts.recoverFetchImpl ? { recoverFetchImpl: opts.recoverFetchImpl } : {}),
    renewBeforeMs: opts.renewBeforeMs ?? DEFAULT_CERT_RENEW_WINDOW_MS,
    ...(opts.timer ? { timer: opts.timer } : {}),
    ...(opts.now ? { now: opts.now } : {}),
--- a/agent/src/certs/rotation.ts
+++ b/agent/src/certs/rotation.ts
@@ -14,12 +14,35 @@ import type { AgentIdentity } from '../keys/identity.js'
 import type { Keystore } from '../keys/keystore.js'
 import type { TimerLike } from '../transport/seams.js'
 import { createBackoff, type BackoffPolicy } from '../transport/backoff.js'
-import { CertExpiredBeyondGraceError } from '../transport/dial.js'
 import { buildCsr } from '../enroll/csr.js'
 import { certResponseToPem } from './pem.js'

 export const DEFAULT_RENEW_BEFORE_MS = 5 * 60_000 // renew 5 min before expiry

+/**
+ * How long after `notAfter` a lapsed leaf may still be swapped for a fresh one (30 days).
+ *
+ * `/renew` is mTLS-authenticated by the very leaf it renews, so a lapsed leaf cannot renew itself —
+ * a deadlock that bricked a host for 8 days in production (the laptop slept through its renewal
+ * window, then the agent logged `client certificate has expired` 6380 times and never recovered).
+ * Inside this window the agent switches to the `/recover` endpoint instead; past it, only a re-pair
+ * can help and the rotator says so once and stops.
+ */
+export const DEFAULT_EXPIRED_RENEW_GRACE_MS = 30 * 24 * 60 * 60 * 1000
+
+/** The leaf lapsed longer ago than the recovery grace allows ⇒ operator must re-pair this host. */
+export class CertExpiredBeyondGraceError extends Error {
+  constructor(
+    /** How long ago the leaf expired (ms) — non-secret, safe to log. */
+    readonly expiredForMs: number,
+    /** The grace window that was exceeded (ms). */
+    readonly graceMs: number,
+  ) {
+    super('client certificate expired beyond the recovery grace window; re-pair required')
+    this.name = 'CertExpiredBeyondGraceError'
+  }
+}
+
 export interface CertRotator {
  start(): void
  stop(): void
@@ -41,34 +64,21 @@ export function renewalUrlFor(cfg: AgentConfig): string {
  return cfg.enrollUrl.replace(/\/enroll$/, '/renew')
 }

-/** The `enroll.<zone>` label the recovery vhost mirrors as `recover.<zone>`. */
-const ENROLL_LABEL = 'enroll.'
-const RECOVER_LABEL = 'recover.'
-
 /**
- * Renewal route for an ALREADY-EXPIRED leaf, or null when this deployment has none.
+ * Recovery route for a leaf that has ALREADY EXPIRED — a sibling PATH on the same enroll host.
 *
- * The normal `/renew` vhost runs `ssl_verify_client optional`, which makes nginx answer a bare
- * `400 Bad Request` as soon as a presented client cert fails verification — an expired leaf never
- * reaches the location, so it can never be forwarded to the control-plane. Recovery therefore lives
- * on a sibling `recover.` vhost running `optional_no_ca`, where nginx forwards the cert unverified
- * and the control-plane is the sole (and full) verifier: chain → SPIFFE → registry status → bounded
- * expiry grace. Explicit `cfg.recoverUrl` wins; otherwise it is derived by swapping the `enroll.`
- * label. A deployment whose enroll host has no `enroll.` label gets null (no recovery configured)
- * rather than a guessed hostname.
+ * It cannot be `/renew`, because nginx will not forward an expired client certificate at all: under
+ * `ssl_verify_client optional` it answers a bare `400 Bad Request`, and `optional_no_ca` does not
+ * help either — nginx only tolerates CHAIN errors there (`ngx_ssl_verify_error_optional` covers
+ * self-signed / unknown-issuer / unverifiable-leaf, NOT `X509_V_ERR_CERT_HAS_EXPIRED`). So recovery
+ * drops mTLS entirely: it is a plain HTTPS POST carrying the expired cert in the BODY. Nothing is
+ * lost by that — the accompanying CSR is self-signed by the same private key, and the control-plane
+ * signer already enforces CSR proof-of-possession plus `CSR key == registered key`, so possession is
+ * proven exactly as the TLS handshake used to prove it.
 */
-export function recoveryRenewalUrlFor(cfg: AgentConfig): string | null {
+export function recoveryUrlFor(cfg: AgentConfig): string {
  if (cfg.recoverUrl != null && cfg.recoverUrl.length > 0) return cfg.recoverUrl
-  let url: URL
-  try {
-    url = new URL(cfg.enrollUrl)
-  } catch {
-    return null
-  }
-  if (!url.hostname.startsWith(ENROLL_LABEL)) return null
-  url.hostname = RECOVER_LABEL + url.hostname.slice(ENROLL_LABEL.length)
-  url.pathname = url.pathname.replace(/\/enroll$/, '/renew')
-  return url.toString()
+  return cfg.enrollUrl.replace(/\/enroll$/, '/recover')
 }

 /** Ms until (validTo − renewBeforeMs), clamped to ≥ 0. */
@@ -110,6 +120,34 @@ export async function renewCert(
  return 'rotated'
 }

+/**
+ * One recovery round-trip for an EXPIRED leaf: plain HTTPS (no client cert — see `recoveryUrlFor`)
+ * POSTing the expired cert alongside a fresh CSR over the SAME key. Same outcome contract as
+ * `renewCert`: 'rotated' installs the new leaf, 403 ⇒ 'revoked', anything else throws to the retry.
+ */
+export async function recoverCert(
+  cfg: AgentConfig,
+  id: AgentIdentity,
+  ks: Keystore,
+  fetchImpl: typeof fetch,
+  url: string = recoveryUrlFor(cfg),
+): Promise<RenewOutcome> {
+  const certs = ks.loadCert()
+  if (certs === null) throw new Error('cannot recover without the expired leaf on disk')
+  const csr = buildCsr(id, cfg.subdomain ?? 'web-terminal-agent')
+  const res = await fetchImpl(url, {
+    method: 'POST',
+    headers: { 'content-type': 'application/json' },
+    body: JSON.stringify({ cert: certs.certPem, csr }),
+  })
+  if (res.status === 403) return 'revoked'
+  if (!res.ok) throw new Error(`cert recovery failed: HTTP ${res.status}`)
+  const json = (await res.json()) as { cert?: unknown; caChain?: unknown }
+  const { certPem, caChainPem } = certResponseToPem(json.cert, json.caChain)
+  ks.saveCert(certPem, caChainPem)
+  return 'rotated'
+}
+
 export function createCertRotator(
  cfg: AgentConfig,
  id: AgentIdentity,
@@ -122,6 +160,10 @@ export function createCertRotator(
    parseCert?: (pem: string) => Date
    /** Backoff policy for retrying a FAILED renewal (default 1s→30s). Reset after a success. */
    retryBackoff?: BackoffPolicy
+    /** Plain (NON-mTLS) fetch used only for the expired-leaf `/recover` call. */
+    recoverFetchImpl?: typeof fetch
+    /** Window in which an expired leaf may still be recovered. 0 ⇒ no recovery at all. */
+    expiredGraceMs?: number
  } = {},
 ): CertRotator {
  const renewBeforeMs = opts.renewBeforeMs ?? DEFAULT_RENEW_BEFORE_MS
@@ -133,6 +175,8 @@ export function createCertRotator(
    clearInterval: (h) => clearInterval(h as ReturnType<typeof setInterval>),
  }
  const doFetch = opts.fetchImpl ?? fetch
+  const recoverFetch = opts.recoverFetchImpl ?? fetch
+  const expiredGraceMs = opts.expiredGraceMs ?? DEFAULT_EXPIRED_RENEW_GRACE_MS
  const now = opts.now ?? (() => new Date())
  const retryBackoff = opts.retryBackoff ?? createBackoff({ jitter: true })
  let handle: unknown = null
@@ -149,20 +193,33 @@ export function createCertRotator(
  }

  /**
-   * Pick the endpoint for THIS attempt. A leaf that has already lapsed cannot be forwarded by the
-   * strict vhost, so it must go to the recovery vhost; a still-valid leaf always uses the normal one.
-   * With no recovery endpoint configured we fall back to the normal URL and let it fail honestly.
+   * How this attempt must be made, derived from how stale the leaf on disk is:
+   *   `normal`    — still valid ⇒ ordinary mTLS `/renew`;
+   *   `recover`   — expired but inside the grace window ⇒ plain `/recover` with the cert in the body;
+   *   `exhausted` — expired past the grace window ⇒ nothing can succeed; only an operator re-pair.
   */
-  function endpointForNow(): string {
+  function attemptPlan(): { mode: 'normal' | 'recover' | 'exhausted'; expiredForMs: number } {
    const certs = ks.loadCert()
-    if (certs === null) return renewalUrlFor(cfg)
-    const expired = parseCert(certs.certPem).getTime() < now().getTime()
-    if (!expired) return renewalUrlFor(cfg)
-    return recoveryRenewalUrlFor(cfg) ?? renewalUrlFor(cfg)
+    if (certs === null) return { mode: 'normal', expiredForMs: 0 }
+    const expiredForMs = now().getTime() - parseCert(certs.certPem).getTime()
+    if (expiredForMs <= 0) return { mode: 'normal', expiredForMs: 0 }
+    return { mode: expiredForMs > expiredGraceMs ? 'exhausted' : 'recover', expiredForMs }
  }

  function runRenewal(): void {
-    void renewCert(cfg, id, ks, doFetch, { url: endpointForNow() })
+    const plan = attemptPlan()
+    if (plan.mode === 'exhausted') {
+      // Terminal: report ONCE and arm nothing. The old code retried forever, which is how a single
+      // real failure turned into 6380 identical warnings that buried the signal.
+      handle = null
+      exhaustedCb?.(new CertExpiredBeyondGraceError(plan.expiredForMs, expiredGraceMs))
+      return
+    }
+    const attempt =
+      plan.mode === 'recover'
+        ? recoverCert(cfg, id, ks, recoverFetch)
+        : renewCert(cfg, id, ks, doFetch)
+    void attempt
      .then((outcome) => {
        if (outcome === 'revoked') {
          revokedCb?.()
@@ -173,14 +230,6 @@ export function createCertRotator(
        schedule()
      })
      .catch((err: unknown) => {
-        // The grace window is spent: no amount of retrying can mint a new leaf, only an operator
-        // re-pair can. Report it ONCE and stop — the old behaviour retried forever and buried the
-        // real signal under thousands of identical warnings.
-        if (err instanceof CertExpiredBeyondGraceError) {
-          handle = null
-          exhaustedCb?.(err)
-          return
-        }
        // Network/HTTP failure (never a 403 revoke): surface it (caller logs, no secret) and retry
        // with backoff. The cert is still valid until expiry, so the tunnel stays up meanwhile — a
        // failed renewal must NEVER tear the supervisor down.
--- a/agent/src/transport/dial.ts
+++ b/agent/src/transport/dial.ts
@@ -21,37 +21,6 @@ export class CertExpiredError extends Error {
  }
 }

-/**
- * Default window during which an ALREADY-EXPIRED leaf may still authenticate a `/renew` (30 days).
- *
- * WHY THIS EXISTS: `/renew` is authenticated by mTLS with the current leaf, so once that leaf lapses
- * the agent can no longer renew it — a deadlock that bricks the host until a manual re-pair (observed
- * in production: the leaf expired while the laptop was asleep through its renewal window, then the
- * agent logged `client certificate has expired; renew before dialling` 6380 times and never
- * recovered). Accepting a recently-expired leaf ONLY for re-issuance breaks the cycle.
- *
- * WHY IT IS SAFE-ENOUGH: the leaf still proves possession of the private key, still has to chain to
- * the frp-client CA, and the control-plane still refuses a host whose registry status is `revoked` —
- * none of those checks are relaxed. The delta is that a STALE stolen credential stays reusable for
- * this window; an attacker holding an UNEXPIRED stolen leaf can already renew indefinitely, so this
- * widens an existing exposure rather than creating a new class of one. It is bounded, and it never
- * applies to the tunnel dial — only to re-issuance.
- */
-export const DEFAULT_EXPIRED_RENEW_GRACE_MS = 30 * 24 * 60 * 60 * 1000
-
-/** The leaf expired so long ago that even the renewal grace is exhausted ⇒ operator must re-pair. */
-export class CertExpiredBeyondGraceError extends Error {
-  constructor(
-    /** How long ago the leaf expired (ms) — non-secret, safe to log. */
-    readonly expiredForMs: number,
-    /** The grace window that was exceeded (ms). */
-    readonly graceMs: number,
-  ) {
-    super('client certificate expired beyond the renewal grace window; re-pair required')
-    this.name = 'CertExpiredBeyondGraceError'
-  }
-}
-
 /** TLS material for the wss client. NOTE: `rejectUnauthorized` is ALWAYS true (anti-MITM). */
 export interface TlsClientOptions {
  readonly cert: string
@@ -75,27 +44,17 @@ const defaultCertParser: CertParser = (pem) => ({ validTo: new Date(new X509Cert
 /**
 * Assemble the mTLS options from the keystore. Throws NotEnrolledError if key/cert are missing,
 * CertExpiredError if the cert is past `validTo`. There is NO token field by construction (INV4).
- *
- * `expiredGraceMs` is the ONLY way to get an expired leaf through, and exists solely for the `/renew`
- * recovery path (see `DEFAULT_EXPIRED_RENEW_GRACE_MS`). Omitted or 0 ⇒ the historical fail-closed
- * behaviour, unchanged; the tunnel dial deliberately never passes it. Past the window the distinct
- * `CertExpiredBeyondGraceError` tells the caller to stop retrying and surface "re-pair required".
 */
 export function buildTlsOptions(
  ks: Keystore,
-  opts: { now?: Date; certParser?: CertParser; expiredGraceMs?: number } = {},
+  opts: { now?: Date; certParser?: CertParser } = {},
 ): TlsClientOptions {
  const id = ks.loadIdentity()
  const certs = ks.loadCert()
  if (id === null || certs === null) throw new NotEnrolledError()
  const parse = opts.certParser ?? defaultCertParser
  const now = opts.now ?? new Date()
-  const expiredForMs = now.getTime() - parse(certs.certPem).validTo.getTime()
-  if (expiredForMs > 0) {
-    const graceMs = opts.expiredGraceMs ?? 0
-    if (graceMs <= 0) throw new CertExpiredError()
-    if (expiredForMs > graceMs) throw new CertExpiredBeyondGraceError(expiredForMs, graceMs)
-  }
+  if (parse(certs.certPem).validTo.getTime() < now.getTime()) throw new CertExpiredError()
  return {
    cert: certs.certPem,
    key: id.exportPrivatePkcs8Pem(),
--- a/agent/test/dial.test.ts
+++ b/agent/test/dial.test.ts
@@ -6,9 +6,7 @@ import type { AgentConfig } from '../src/config/agentConfig.js'
 import { generateIdentity } from '../src/keys/identity.js'
 import { openKeystore } from '../src/keys/keystore.js'
 import {
-  CertExpiredBeyondGraceError,
  CertExpiredError,
-  DEFAULT_EXPIRED_RENEW_GRACE_MS,
  NotEnrolledError,
  buildTlsOptions,
  dialRelay,
@@ -67,82 +65,6 @@ describe('buildTlsOptions (T12, INV14/INV4)', () => {
  })
 })

-/**
- * Expired-leaf RENEWAL grace. The tunnel dial stays fail-closed forever; only the /renew recovery
- * path may opt in, and only inside a bounded window — otherwise an expired leaf deadlocks the agent
- * (mTLS renew needs a cert, and the only cert has expired) and the host is bricked until a re-pair.
- */
-describe('buildTlsOptions expired-renewal grace (deadlock recovery)', () => {
-  const expiredBy = (ms: number) => () => ({ validTo: new Date(Date.now() - ms) })
-  const DAY = 86_400_000
-
-  it('stays fail-closed by DEFAULT — no grace opt-in ⇒ CertExpiredError', () => {
-    const { dir, ks } = enrolledKs()
-    expect(() => buildTlsOptions(ks, { certParser: expiredBy(DAY) })).toThrow(CertExpiredError)
-    rmSync(dir, { recursive: true, force: true })
-  })
-
-  it('expired INSIDE the grace window → returns options so /renew can authenticate', () => {
-    const { dir, ks } = enrolledKs()
-    const tls = buildTlsOptions(ks, {
-      certParser: expiredBy(8 * DAY),
-      expiredGraceMs: DEFAULT_EXPIRED_RENEW_GRACE_MS,
-    })
-    expect(tls.cert).toBe('CERTPEM')
-    expect(tls.rejectUnauthorized).toBe(true)
-    rmSync(dir, { recursive: true, force: true })
-  })
-
-  it('expired BEYOND the grace window → CertExpiredBeyondGraceError (re-pair required)', () => {
-    const { dir, ks } = enrolledKs()
-    expect(() =>
-      buildTlsOptions(ks, {
-        certParser: expiredBy(31 * DAY),
-        expiredGraceMs: DEFAULT_EXPIRED_RENEW_GRACE_MS,
-      }),
-    ).toThrow(CertExpiredBeyondGraceError)
-    rmSync(dir, { recursive: true, force: true })
-  })
-
-  it('grace of 0 is not a bypass — an expired leaf still throws', () => {
-    const { dir, ks } = enrolledKs()
-    expect(() => buildTlsOptions(ks, { certParser: expiredBy(1000), expiredGraceMs: 0 })).toThrow(
-      CertExpiredError,
-    )
-    rmSync(dir, { recursive: true, force: true })
-  })
-
-  it('a still-valid cert is unaffected by the grace option', () => {
-    const { dir, ks } = enrolledKs()
-    const tls = buildTlsOptions(ks, {
-      certParser: future,
-      expiredGraceMs: DEFAULT_EXPIRED_RENEW_GRACE_MS,
-    })
-    expect(tls.cert).toBe('CERTPEM')
-    rmSync(dir, { recursive: true, force: true })
-  })
-
-  it('the TUNNEL dial never gets grace — an expired leaf still refuses to dial', () => {
-    const { dir, ks } = enrolledKs()
-    let constructed = 0
-    class NeverCtor implements RawTlsWs {
-      constructor() {
-        constructed += 1
-      }
-      send(): void {}
-      close(): void {}
-      on(): void {}
-      once(): void {}
-    }
-    // `dialRelay` has no grace seam at all: it fails fast (synchronously) before any socket exists.
-    expect(() =>
-      dialRelay(CFG, ks, { Ctor: NeverCtor as unknown as TlsWsConstructor, certParser: past }),
-    ).toThrow(CertExpiredError)
-    expect(constructed).toBe(0)
-    rmSync(dir, { recursive: true, force: true })
-  })
-})
-
 describe('dialRelay (T12)', () => {
  it('constructs the wss client with the TLS options and resolves on open', async () => {
    const { dir, ks } = enrolledKs()
--- a/agent/test/nativeRenew.test.ts
+++ b/agent/test/nativeRenew.test.ts
@@ -27,10 +27,7 @@ import {
  type MtlsRequest,
 } from '../src/certs/nativeRenew.js'
 import { FakeTimer } from './fixtures/fakes.js'
-import {
-  CertExpiredBeyondGraceError,
-  DEFAULT_EXPIRED_RENEW_GRACE_MS,
-} from '../src/transport/dial.js'
+import { CertExpiredBeyondGraceError } from '../src/certs/rotation.js'

 const CFG: AgentConfig = {
  relayUrl: 'wss://relay/agent',
@@ -296,38 +293,26 @@ describe('startNativeAutoRenew (A5 end-to-end)', () => {
 })

 /**
- * Expired-leaf recovery. `createMtlsFetch` is the ONE place that decides whether a lapsed leaf may
- * still be presented; if it keeps refusing (the pre-fix behaviour) the renewal can never leave the
- * host and the tunnel stays dead until a manual re-pair.
+ * The mTLS renew transport stays STRICT about expiry: nginx refuses to forward an expired client
+ * cert at all, so an expired leaf must be routed to the plain `/recover` endpoint by the rotator
+ * rather than smuggled through this transport.
 */
-describe('createMtlsFetch expired-leaf recovery', () => {
-  const expiredBy = (ms: number) => () => ({ validTo: new Date(Date.now() - ms) })
-  const DAY = 86_400_000
-
-  it('still presents a leaf that expired INSIDE the grace window (renewal can go out)', async () => {
+describe('createMtlsFetch stays fail-closed on an expired leaf', () => {
+  it('refuses to present a lapsed leaf (recovery is the rotator\'s job, not this transport\'s)', async () => {
    const { dir, ks } = enrolledKs()
-    let presented = ''
-    const request: MtlsRequest = async (_url, tls) => {
-      presented = tls.cert
+    let called = 0
+    const request: MtlsRequest = async () => {
+      called += 1
      return { status: 201, body: '{}' }
    }
-    const f = createMtlsFetch(ks, { request, certParser: expiredBy(8 * DAY) })
-    const res = await f('https://recover.example.com/renew', { method: 'POST', body: '{}' })
-    expect(res.status).toBe(201)
-    expect(presented).toBe('LEAFCERT')
-    rmSync(dir, { recursive: true, force: true })
-  })
-
-  it('refuses once the leaf is BEYOND the grace window (terminal — re-pair required)', async () => {
-    const { dir, ks } = enrolledKs()
-    const request: MtlsRequest = async () => ({ status: 201, body: '{}' })
    const f = createMtlsFetch(ks, {
      request,
-      certParser: expiredBy(DEFAULT_EXPIRED_RENEW_GRACE_MS + DAY),
+      certParser: () => ({ validTo: new Date(Date.now() - 86_400_000) }),
    })
-    await expect(f('https://recover.example.com/renew', { method: 'POST' })).rejects.toThrow(
-      CertExpiredBeyondGraceError,
+    await expect(f('https://cp.example.com/renew', { method: 'POST' })).rejects.toThrow(
+      /expired/i,
    )
+    expect(called).toBe(0)
    rmSync(dir, { recursive: true, force: true })
  })
 })
--- a/agent/test/rotation.test.ts
+++ b/agent/test/rotation.test.ts
@@ -8,11 +8,12 @@ import { openKeystore } from '../src/keys/keystore.js'
 import {
  computeRenewDelayMs,
  createCertRotator,
-  recoveryRenewalUrlFor,
+  recoverCert,
+  recoveryUrlFor,
  renewCert,
  renewalUrlFor,
 } from '../src/certs/rotation.js'
-import { CertExpiredBeyondGraceError } from '../src/transport/dial.js'
+import { CertExpiredBeyondGraceError } from '../src/certs/rotation.js'
 import { createBackoff } from '../src/transport/backoff.js'
 import { FakeTimer } from './fixtures/fakes.js'

@@ -164,99 +165,128 @@ describe('createCertRotator (T13)', () => {

 /**
 * Expired-leaf recovery (production deadlock, 2026-07): `/renew` is mTLS-authenticated by the leaf
- * it renews, so a lapsed leaf can never renew itself. Recovery needs BOTH a different endpoint (the
- * strict nginx vhost rejects an expired client cert with a bare 400 before any location runs) and a
- * terminal signal when even the grace window is spent, so the agent stops retrying forever.
+ * it renews, so a lapsed leaf can never renew itself — and nginx will not even forward an expired
+ * client cert. Recovery is therefore a PLAIN POST to `/recover` carrying the expired cert in the
+ * body, plus a terminal signal once the grace window is spent so the agent stops retrying forever.
 */
-describe('expired-leaf recovery routing', () => {
-  it('derives the recovery endpoint from an `enroll.` host', () => {
-    expect(recoveryRenewalUrlFor({ ...CFG, enrollUrl: 'https://enroll.terminal.example.com/enroll' })).toBe(
-      'https://recover.terminal.example.com/renew',
+describe('expired-leaf recovery', () => {
+  const HOUR = 3_600_000
+
+  it('derives /recover as a sibling PATH on the same enroll host', () => {
+    expect(recoveryUrlFor({ ...CFG, enrollUrl: 'https://enroll.terminal.example.com/enroll' })).toBe(
+      'https://enroll.terminal.example.com/recover',
    )
  })

  it('honours an explicit recoverUrl over the derivation', () => {
-    expect(
-      recoveryRenewalUrlFor({
-        ...CFG,
-        enrollUrl: 'https://enroll.terminal.example.com/enroll',
-        recoverUrl: 'https://elsewhere.example.com/renew',
-      }),
-    ).toBe('https://elsewhere.example.com/renew')
+    expect(recoveryUrlFor({ ...CFG, recoverUrl: 'https://elsewhere.example.com/recover' })).toBe(
+      'https://elsewhere.example.com/recover',
+    )
  })

-  it('is null when the enroll host carries no `enroll.` label (nothing to derive)', () => {
-    expect(recoveryRenewalUrlFor(CFG)).toBeNull()
-  })
-
-  it('posts to the NORMAL endpoint while the leaf is still valid', async () => {
+  it('recoverCert posts the EXPIRED cert plus a CSR, with no client cert, and installs the result', async () => {
    const { dir, ks } = enrolledKs()
-    const timer = new FakeTimer()
-    const urls: string[] = []
-    const rotator = createCertRotator(
+    let seenUrl = ''
+    let seenBody: { cert?: string; csr?: string } = {}
+    const fetchImpl = (async (u: string, init: { body: string }) => {
+      seenUrl = u
+      seenBody = JSON.parse(init.body)
+      return jsonRes(201, { cert: 'FRESHCERT', caChain: ['FRESHCA'] })
+    }) as unknown as typeof fetch
+
+    const outcome = await recoverCert(
      { ...CFG, enrollUrl: 'https://enroll.terminal.example.com/enroll' },
      ks.loadIdentity()!,
      ks,
-      {
-        timer,
-        renewBeforeMs: 1000,
-        fetchImpl: (async (u: string) => {
-          urls.push(u)
-          return jsonRes(200, { cert: 'NEWCERT', caChain: ['NEWCA'] })
-        }) as unknown as typeof fetch,
-        now: () => new Date(0),
-        parseCert: () => new Date(2000), // still valid at now=0
-      },
+      fetchImpl,
    )
-    rotator.start()
-    timer.advance(1000)
-    await flush()
-    expect(urls).toEqual(['https://enroll.terminal.example.com/renew'])
-    rotator.stop()
+    expect(outcome).toBe('rotated')
+    expect(seenUrl).toBe('https://enroll.terminal.example.com/recover')
+    expect(seenBody.cert).toBe('OLDCERT') // the lapsed leaf travels in the BODY, not the TLS layer
+    expect(seenBody.csr).toBeTruthy()
+    expect(ks.loadCert()!.certPem).toContain('FRESHCERT')
    rmSync(dir, { recursive: true, force: true })
  })

-  it('posts to the RECOVERY endpoint once the leaf has already expired', async () => {
+  it('a still-valid leaf uses the mTLS /renew fetch, never the recovery one', async () => {
    const { dir, ks } = enrolledKs()
    const timer = new FakeTimer()
-    const urls: string[] = []
-    const rotator = createCertRotator(
-      { ...CFG, enrollUrl: 'https://enroll.terminal.example.com/enroll' },
-      ks.loadIdentity()!,
-      ks,
-      {
-        timer,
-        renewBeforeMs: 1000,
-        fetchImpl: (async (u: string) => {
-          urls.push(u)
-          return jsonRes(200, { cert: 'NEWCERT', caChain: ['NEWCA'] })
-        }) as unknown as typeof fetch,
-        now: () => new Date(10_000),
-        parseCert: () => new Date(2000), // expired 8s ago ⇒ delay clamps to 0
-      },
-    )
-    rotator.start()
-    timer.advance(0)
-    await flush()
-    expect(urls).toEqual(['https://recover.terminal.example.com/renew'])
-    rotator.stop()
-    rmSync(dir, { recursive: true, force: true })
-  })
-
-  it('fires onExhausted and STOPS retrying when the grace window is spent', async () => {
-    const { dir, ks } = enrolledKs()
-    const timer = new FakeTimer()
-    let attempts = 0
+    let renewCalls = 0
+    let recoverCalls = 0
    const rotator = createCertRotator(CFG, ks.loadIdentity()!, ks, {
      timer,
      renewBeforeMs: 1000,
-      retryBackoff: createBackoff({ baseMs: 500, jitter: false }),
      fetchImpl: (async () => {
-        attempts += 1
-        throw new CertExpiredBeyondGraceError(40 * 86_400_000, 30 * 86_400_000)
+        renewCalls += 1
+        return jsonRes(200, { cert: 'NEWCERT', caChain: ['NEWCA'] })
+      }) as unknown as typeof fetch,
+      recoverFetchImpl: (async () => {
+        recoverCalls += 1
+        return jsonRes(200, {})
      }) as unknown as typeof fetch,
      now: () => new Date(0),
-      parseCert: () => new Date(2000),
+      parseCert: () => new Date(2000), // valid at now=0
+    })
+    rotator.start()
+    timer.advance(1000)
+    await flush()
+    expect(renewCalls).toBe(1)
+    expect(recoverCalls).toBe(0)
+    rotator.stop()
+    rmSync(dir, { recursive: true, force: true })
+  })
+
+  it('an expired leaf INSIDE the grace window switches to the recovery fetch', async () => {
+    const { dir, ks } = enrolledKs()
+    const timer = new FakeTimer()
+    let renewCalls = 0
+    let recoverCalls = 0
+    const rotator = createCertRotator(CFG, ks.loadIdentity()!, ks, {
+      timer,
+      renewBeforeMs: 1000,
+      expiredGraceMs: 30 * 24 * HOUR,
+      fetchImpl: (async () => {
+        renewCalls += 1
+        return jsonRes(200, {})
+      }) as unknown as typeof fetch,
+      recoverFetchImpl: (async () => {
+        recoverCalls += 1
+        return jsonRes(201, { cert: 'NEWCERT', caChain: ['NEWCA'] })
+      }) as unknown as typeof fetch,
+      now: () => new Date(8 * 24 * HOUR), // 8 days after the leaf lapsed
+      parseCert: () => new Date(0),
+    })
+    let rotated = 0
+    rotator.onRotated(() => {
+      rotated += 1
+    })
+    rotator.start()
+    timer.advance(0)
+    await flush()
+    expect(recoverCalls).toBe(1)
+    expect(renewCalls).toBe(0)
+    expect(rotated).toBe(1)
+    rotator.stop()
+    rmSync(dir, { recursive: true, force: true })
+  })
+
+  it('BEYOND the grace window it fires onExhausted, issues no request, and stops retrying', async () => {
+    const { dir, ks } = enrolledKs()
+    const timer = new FakeTimer()
+    let requests = 0
+    const countingFetch = (async () => {
+      requests += 1
+      return jsonRes(201, {})
+    }) as unknown as typeof fetch
+    const rotator = createCertRotator(CFG, ks.loadIdentity()!, ks, {
+      timer,
+      renewBeforeMs: 1000,
+      expiredGraceMs: 30 * 24 * HOUR,
+      retryBackoff: createBackoff({ baseMs: 500, jitter: false }),
+      fetchImpl: countingFetch,
+      recoverFetchImpl: countingFetch,
+      now: () => new Date(31 * 24 * HOUR), // 31 days stale ⇒ past a 30-day grace
+      parseCert: () => new Date(0),
    })
    const errors: unknown[] = []
    let exhausted: CertExpiredBeyondGraceError | null = null
@@ -265,17 +295,16 @@ describe('expired-leaf recovery routing', () => {
      exhausted = e
    })
    rotator.start()
-    timer.advance(1000)
+    timer.advance(0)
    await flush()

-    expect(attempts).toBe(1)
    expect(exhausted).toBeInstanceOf(CertExpiredBeyondGraceError)
-    // Terminal: no retry is armed, because only a re-pair can help — retrying forever is the log
-    // spam that buried the real signal in production (6380 identical warnings).
+    expect(requests).toBe(0) // nothing is even attempted — it cannot succeed
    expect(errors).toHaveLength(0)
+    // Terminal: no retry armed. Retrying forever is what produced 6380 identical warnings.
    timer.advance(60_000)
    await flush()
-    expect(attempts).toBe(1)
+    expect(requests).toBe(0)
    rmSync(dir, { recursive: true, force: true })
  })
 })
--- a/control-plane/node_modules
+++ b/control-plane/node_modules
@@ -0,0 +1 @@
+/Users/yiukai/Documents/git/web-terminal/control-plane/node_modules
--- a/control-plane/src/api/renew.ts
+++ b/control-plane/src/api/renew.ts
@@ -51,6 +51,8 @@ export const DEFAULT_RENEW_RATE_WINDOW_MS = 60 * 60 * 1000
 export const RENEW_RATE_MAX_IDENTITIES = 10_000
 /** Max base64 length of a submitted CSR (a P-256 PKCS#10 is well under 1 KB; this is generous slack). */
 export const MAX_CSR_B64_LEN = 8192
+/** Max wire length of a body-carried certificate (a P-256 leaf PEM is ~1 KB; generous slack). */
+export const MAX_PRESENTED_CERT_LEN = 16384
 /**
 * Default header the mTLS terminator forwards the verified client cert in (base64 DER). The terminator
 * MUST set this from `$ssl_client_cert` AND strip any client-supplied copy — a client can never provide
@@ -185,23 +187,29 @@ export function headerPresentedCert(headerName: string = DEFAULT_CLIENT_CERT_HEA
      const raw = req.headers[name]
      const value = Array.isArray(raw) ? raw[0] : raw
      if (typeof value !== 'string' || value.length === 0) return null
-      try {
-        // The terminator may forward the verified cert as base64 DER, OR as PEM — including nginx's
-        // header-safe `$ssl_client_escaped_cert` (URL-encoded PEM). Normalize all three to raw DER:
-        // URL-decode if escaped, then strip PEM armor + whitespace to recover the base64 DER body.
-        let s = value.includes('%') ? safeDecodeUri(value) : value
-        if (s.includes('BEGIN CERTIFICATE')) {
-          s = s.replace(/-----[^-]+-----/g, '').replace(/\s+/g, '')
-        }
-        const der = Buffer.from(s, 'base64')
-        return der.length > 0 ? new Uint8Array(der) : null
-      } catch {
-        return null
-      }
+      return certWireToDer(value)
    },
  }
 }

+/**
+ * Normalize a certificate carried over the wire to raw DER. Accepts base64 DER, PEM, and nginx's
+ * header-safe `$ssl_client_escaped_cert` (URL-encoded PEM): URL-decode if escaped, then strip PEM
+ * armor + whitespace to recover the base64 body. Returns null on anything unparseable.
+ */
+export function certWireToDer(value: string): Uint8Array | null {
+  try {
+    let s = value.includes('%') ? safeDecodeUri(value) : value
+    if (s.includes('BEGIN CERTIFICATE')) {
+      s = s.replace(/-----[^-]+-----/g, '').replace(/\s+/g, '')
+    }
+    const der = Buffer.from(s, 'base64')
+    return der.length > 0 ? new Uint8Array(der) : null
+  } catch {
+    return null
+  }
+}
+
 /** URL-decode `value`, returning it unchanged if it is not valid percent-encoding. */
 function safeDecodeUri(value: string): string {
  try {
@@ -286,6 +294,13 @@ function parsePresentedCertIdentity(
 }

 const RenewBodySchema = z.object({ csr: z.string().min(1).max(MAX_CSR_B64_LEN) }).strict()
+/** `/recover` additionally carries the EXPIRED leaf itself (base64 DER or PEM). */
+const RecoverBodySchema = z
+  .object({
+    cert: z.string().min(1).max(MAX_PRESENTED_CERT_LEN),
+    csr: z.string().min(1).max(MAX_CSR_B64_LEN),
+  })
+  .strict()

 export interface RenewDeps {
  readonly hosts: HostRegistry
@@ -327,7 +342,9 @@ function sendError(reply: FastifyReply, err: unknown): void {
 export function buildRenewRouter(deps: RenewDeps): FastifyPluginAsync {
  const presentedCert = deps.presentedCert ?? headerPresentedCert()
  const rateLimiter = deps.rateLimiter ?? createRenewRateLimiter()
-  const expiredGraceMs = deps.expiredRenewGraceMs ?? DEFAULT_EXPIRED_RENEW_GRACE_MS
+  // `/renew` stays STRICT (0): the mTLS terminator would never forward an expired cert to it anyway.
+  // The grace belongs to `/recover`, the route built for exactly that case.
+  const recoverGraceMs = deps.expiredRenewGraceMs ?? DEFAULT_EXPIRED_RENEW_GRACE_MS

  return async (app) => {
    app.post('/renew', async (req, reply) => {
@@ -338,7 +355,7 @@ export function buildRenewRouter(deps: RenewDeps): FastifyPluginAsync {
          der,
          'host',
          deps.hostCaAnchorsDer
-            ? { caAnchorsDer: deps.hostCaAnchorsDer, nowMs: Date.now(), expiredGraceMs }
+            ? { caAnchorsDer: deps.hostCaAnchorsDer, nowMs: Date.now(), expiredGraceMs: 0 }
            : undefined,
        )
        rateLimiter.check(`host:${identity.accountId}:${identity.id}`)
@@ -365,6 +382,57 @@ export function buildRenewRouter(deps: RenewDeps): FastifyPluginAsync {
      }
    })

+    /**
+     * Expired-leaf recovery. The lapsed cert arrives in the BODY because no TLS terminator will
+     * forward an expired client certificate (nginx `optional` → bare 400; `optional_no_ca` tolerates
+     * only chain errors, never `X509_V_ERR_CERT_HAS_EXPIRED`). That makes this route the SOLE
+     * verifier, so it runs the identical trust pipeline as `/renew` — real X.509 path validation to
+     * the frp-client-CA anchors, SPIFFE parse, `notBefore`, registry `active` + account match — and
+     * differs ONLY in allowing a bounded overrun on `notAfter`.
+     *
+     * Possession of the private key is still proven: the CSR is self-signed by it, and the host
+     * signer's delegated gate enforces CSR PoP plus `CSR key == registered key`. A replayed cert
+     * without the key therefore yields, at most, a certificate the attacker cannot authenticate with.
+     * The header channel is deliberately IGNORED here — on this route only the body speaks.
+     */
+    app.post('/recover', async (req, reply) => {
+      try {
+        const body = RecoverBodySchema.parse(req.body)
+        const der = certWireToDer(body.cert)
+        if (der === null) throw new RenewRejectError(401)
+        const identity = parsePresentedCertIdentity(
+          der,
+          'host',
+          deps.hostCaAnchorsDer
+            ? {
+                caAnchorsDer: deps.hostCaAnchorsDer,
+                nowMs: Date.now(),
+                expiredGraceMs: recoverGraceMs,
+              }
+            : undefined,
+        )
+        rateLimiter.check(`recover:${identity.accountId}:${identity.id}`)
+
+        const host = await deps.hosts.getHostBySubdomain(identity.id)
+        if (host === null || host.status === 'revoked' || host.accountId !== identity.accountId) {
+          throw new RenewRejectError(403)
+        }
+
+        const leaf = await deps.renewer.renewHostLeaf(
+          host.hostId,
+          identity.publicKeySpki,
+          decodeCsrWire(body.csr),
+        )
+        await reply.code(201).send({
+          cert: bytesToBase64(leaf.cert),
+          caChain: leaf.caChain.map((c) => bytesToBase64(c)),
+          notAfter: leaf.notAfter.toISOString(),
+        })
+      } catch (err) {
+        sendError(reply, err)
+      }
+    })
+
    app.post('/device/:id/renew', async (req, reply) => {
      try {
        const der = presentedCert.presentedCertDer(req)
@@ -373,7 +441,7 @@ export function buildRenewRouter(deps: RenewDeps): FastifyPluginAsync {
          der,
          'device',
          deps.deviceCaAnchorsDer
-            ? { caAnchorsDer: deps.deviceCaAnchorsDer, nowMs: Date.now(), expiredGraceMs }
+            ? { caAnchorsDer: deps.deviceCaAnchorsDer, nowMs: Date.now(), expiredGraceMs: 0 }
            : undefined,
        )
        const id = (req.params as { id: string }).id
--- a/control-plane/test/renew.test.ts
+++ b/control-plane/test/renew.test.ts
@@ -490,65 +490,10 @@ describe('CP6c POST /renew — presented current-cert chain + expiry verificatio
    expect(res.statusCode).toBe(201)
  })

-  /**
-   * POLICY CHANGE (expired-leaf deadlock fix): `/renew` is mTLS-authenticated by the very leaf it
-   * renews, so refusing every expired leaf meant a host whose leaf lapsed could NEVER renew and was
-   * bricked until a manual re-pair. A recently-expired leaf is now accepted for RE-ISSUANCE ONLY,
-   * inside a bounded window. Everything else stays fail-closed — the tests below pin that down.
-   */
-  test('a leaf expired INSIDE the grace window renews → 201 (breaks the deadlock)', async () => {
-    const ctx = await hostCtx('alice')
-    const now = Date.now()
-    const expired = await mintHostLeaf(ctx, new Date(now - 9 * DAY_MS), new Date(now - 8 * DAY_MS))
-    const app = appWith(hostDeps(ctx, { hostCaAnchorsDer: [ctx.ca.caDer] }))
-    await app.ready()
-    const res = await app.inject({
-      method: 'POST',
-      url: '/renew',
-      headers: { 'x-client-cert': certHeader(expired) },
-      payload: { csr: b64Csr(ctx.csr) },
-    })
-    expect(res.statusCode).toBe(201)
-  })
-
-  test('a leaf expired BEYOND the grace window is rejected → 401', async () => {
-    const ctx = await hostCtx('alice')
-    const now = Date.now()
-    const stale = await mintHostLeaf(ctx, new Date(now - 60 * DAY_MS), new Date(now - 31 * DAY_MS))
-    const app = appWith(hostDeps(ctx, { hostCaAnchorsDer: [ctx.ca.caDer] }))
-    await app.ready()
-    const res = await app.inject({
-      method: 'POST',
-      url: '/renew',
-      headers: { 'x-client-cert': certHeader(stale) },
-      payload: { csr: b64Csr(ctx.csr) },
-    })
-    expect(res.statusCode).toBe(401)
-  })
-
-  test('grace 0 restores the strict fail-closed behaviour → 401', async () => {
+  test('an EXPIRED current cert (valid chain, notAfter in the past) is rejected → 401', async () => {
    const ctx = await hostCtx('alice')
    const now = Date.now()
    const expired = await mintHostLeaf(ctx, new Date(now - 2 * DAY_MS), new Date(now - DAY_MS))
-    const app = appWith(
-      hostDeps(ctx, { hostCaAnchorsDer: [ctx.ca.caDer], expiredRenewGraceMs: 0 }),
-    )
-    await app.ready()
-    const res = await app.inject({
-      method: 'POST',
-      url: '/renew',
-      headers: { 'x-client-cert': certHeader(expired) },
-      payload: { csr: b64Csr(ctx.csr) },
-    })
-    expect(res.statusCode).toBe(401)
-  })
-
-  test('grace NEVER bypasses revocation — revoked host with an in-grace leaf → 403', async () => {
-    const ctx = await hostCtx('alice')
-    const now = Date.now()
-    const expired = await mintHostLeaf(ctx, new Date(now - 9 * DAY_MS), new Date(now - 8 * DAY_MS))
-    const host = await ctx.hosts.getHostBySubdomain('alice')
-    await ctx.hosts.setHostStatus(host!.hostId, 'revoked')
    const app = appWith(hostDeps(ctx, { hostCaAnchorsDer: [ctx.ca.caDer] }))
    await app.ready()
    const res = await app.inject({
@@ -557,42 +502,8 @@ describe('CP6c POST /renew — presented current-cert chain + expiry verificatio
      headers: { 'x-client-cert': certHeader(expired) },
      payload: { csr: b64Csr(ctx.csr) },
    })
-    expect(res.statusCode).toBe(403)
-  })
-
-  test('grace NEVER bypasses chain validation — untrusted CA + in-grace leaf → 401', async () => {
-    const ctx = await hostCtx('alice')
-    const rogueCa = await makeP256Ca('rogue-CA')
-    const now = Date.now()
-    const rogue = await mintHostLeaf(
-      ctx,
-      new Date(now - 9 * DAY_MS),
-      new Date(now - 8 * DAY_MS),
-      rogueCa.caSigner,
-    )
-    const app = appWith(hostDeps(ctx, { hostCaAnchorsDer: [ctx.ca.caDer] }))
-    await app.ready()
-    const res = await app.inject({
-      method: 'POST',
-      url: '/renew',
-      headers: { 'x-client-cert': certHeader(rogue) },
-      payload: { csr: b64Csr(ctx.csr) },
-    })
-    expect(res.statusCode).toBe(401)
-  })
-
-  test('grace applies ONLY to notAfter — a not-yet-valid leaf is still rejected → 401', async () => {
-    const ctx = await hostCtx('alice')
-    const now = Date.now()
-    const future = await mintHostLeaf(ctx, new Date(now + DAY_MS), new Date(now + 2 * DAY_MS))
-    const app = appWith(hostDeps(ctx, { hostCaAnchorsDer: [ctx.ca.caDer] }))
-    await app.ready()
-    const res = await app.inject({
-      method: 'POST',
-      url: '/renew',
-      headers: { 'x-client-cert': certHeader(future) },
-      payload: { csr: b64Csr(ctx.csr) },
-    })
+    // STRICT on this route: nginx would never forward an expired client cert here anyway, so the
+    // deadlock escape hatch lives on `/recover` (below) and NOT on the mTLS renewal path.
    expect(res.statusCode).toBe(401)
  })

@@ -612,3 +523,152 @@ describe('CP6c POST /renew — presented current-cert chain + expiry verificatio
    expect(res.statusCode).toBe(401)
  })
 })
+
+/**
+ * CP6d · POST /recover — the expired-leaf escape hatch.
+ *
+ * Unlike `/renew` this route is NOT mTLS-authenticated: nginx cannot forward an expired client cert
+ * (under `ssl_verify_client optional` it 400s, and `optional_no_ca` only tolerates CHAIN errors, not
+ * `X509_V_ERR_CERT_HAS_EXPIRED`). The lapsed cert therefore arrives in the BODY, and the
+ * control-plane becomes the sole verifier. These tests pin down that nothing except the `notAfter`
+ * bound was relaxed — chain, SPIFFE, `notBefore`, and registry status all still decide.
+ */
+describe('CP6d POST /recover — expired-leaf recovery', () => {
+  async function mintLeaf(
+    ctx: HostCtx,
+    notBefore: Date,
+    notAfter: Date,
+    signer = ctx.ca.caSigner,
+  ): Promise<Uint8Array> {
+    const spiffe = `spiffe://relay.terminal.yaojia.wang/account/${ctx.accountId}/host/${ctx.subdomain}`
+    return assembleCertificate({
+      subjectPublicKey: ctx.spki,
+      subject: `CN=${ctx.subdomain}`,
+      issuer: ctx.ca.caCert.subjectName,
+      serialNumber: Uint8Array.from([0x0b]),
+      notBefore,
+      notAfter,
+      extensions: [
+        new x509.SubjectAlternativeNameExtension([
+          { type: 'dns', value: `${ctx.subdomain}.terminal.yaojia.wang` },
+          { type: 'url', value: spiffe },
+        ]),
+        new x509.BasicConstraintsExtension(false, undefined, true),
+        new x509.KeyUsagesExtension(x509.KeyUsageFlags.digitalSignature, true),
+        new x509.ExtendedKeyUsageExtension([x509.ExtendedKeyUsage.clientAuth]),
+      ],
+      signer,
+      sigAlg: 'ecdsa-p256',
+    })
+  }
+
+  const b64 = (der: Uint8Array): string => Buffer.from(der).toString('base64')
+
+  async function post(ctx: HostCtx, cert: Uint8Array, extra?: Partial<RenewDeps>) {
+    const app = appWith(hostDeps(ctx, { hostCaAnchorsDer: [ctx.ca.caDer], ...extra }))
+    await app.ready()
+    return app.inject({
+      method: 'POST',
+      url: '/recover',
+      payload: { cert: b64(cert), csr: b64Csr(ctx.csr) },
+    })
+  }
+
+  test('a leaf expired INSIDE the grace window is re-issued → 201 (breaks the deadlock)', async () => {
+    const ctx = await hostCtx('alice')
+    const now = Date.now()
+    const res = await post(ctx, await mintLeaf(ctx, new Date(now - 9 * DAY_MS), new Date(now - 8 * DAY_MS)))
+    expect(res.statusCode).toBe(201)
+    expect(JSON.parse(res.payload).cert).toBeTruthy()
+  })
+
+  test('a leaf expired BEYOND the grace window is refused → 401', async () => {
+    const ctx = await hostCtx('alice')
+    const now = Date.now()
+    const res = await post(ctx, await mintLeaf(ctx, new Date(now - 60 * DAY_MS), new Date(now - 31 * DAY_MS)))
+    expect(res.statusCode).toBe(401)
+  })
+
+  test('grace 0 disables recovery entirely → 401', async () => {
+    const ctx = await hostCtx('alice')
+    const now = Date.now()
+    const res = await post(
+      ctx,
+      await mintLeaf(ctx, new Date(now - 2 * DAY_MS), new Date(now - DAY_MS)),
+      { expiredRenewGraceMs: 0 },
+    )
+    expect(res.statusCode).toBe(401)
+  })
+
+  /**
+   * THE load-bearing test for this route. nginx no longer validates the chain here, so a forged
+   * self-signed cert carrying a correct-looking SPIFFE SAN must be rejected by the control-plane
+   * alone. If this ever goes green-to-red, `/recover` becomes an unauthenticated cert vending machine.
+   */
+  test('a self-signed cert with a FORGED SPIFFE SAN is refused → 401', async () => {
+    const ctx = await hostCtx('alice')
+    const rogueCa = await makeP256Ca('rogue-CA')
+    const now = Date.now()
+    const rogue = await mintLeaf(
+      ctx,
+      new Date(now - 9 * DAY_MS),
+      new Date(now - 8 * DAY_MS),
+      rogueCa.caSigner,
+    )
+    const res = await post(ctx, rogue)
+    expect(res.statusCode).toBe(401)
+  })
+
+  test('recovery NEVER bypasses revocation — revoked host → 403', async () => {
+    const ctx = await hostCtx('alice')
+    const now = Date.now()
+    const cert = await mintLeaf(ctx, new Date(now - 9 * DAY_MS), new Date(now - 8 * DAY_MS))
+    const host = await ctx.hosts.getHostBySubdomain('alice')
+    await ctx.hosts.setHostStatus(host!.hostId, 'revoked')
+    const res = await post(ctx, cert)
+    expect(res.statusCode).toBe(403)
+  })
+
+  test('grace covers notAfter ONLY — a not-yet-valid leaf is refused → 401', async () => {
+    const ctx = await hostCtx('alice')
+    const now = Date.now()
+    const res = await post(ctx, await mintLeaf(ctx, new Date(now + DAY_MS), new Date(now + 2 * DAY_MS)))
+    expect(res.statusCode).toBe(401)
+  })
+
+  test('a still-valid leaf may also use /recover → 201', async () => {
+    const ctx = await hostCtx('alice')
+    const res = await post(ctx, ctx.currentCertDer)
+    expect(res.statusCode).toBe(201)
+  })
+
+  test('a missing cert field is rejected → 400 (uniform schema reject, same as a missing csr)', async () => {
+    const ctx = await hostCtx('alice')
+    const app = appWith(hostDeps(ctx, { hostCaAnchorsDer: [ctx.ca.caDer] }))
+    await app.ready()
+    const res = await app.inject({ method: 'POST', url: '/recover', payload: { csr: b64Csr(ctx.csr) } })
+    // The module answers with uniform rejects that never say which check failed: 400 for a malformed
+    // body, 401 for a cert that parses but is not trusted, 403 for a trusted cert that is not allowed.
+    expect(res.statusCode).toBe(400)
+  })
+
+  /**
+   * The header is the mTLS terminator's channel. On `/recover` the cert comes from the body, so a
+   * client-supplied header must not be able to substitute an identity.
+   */
+  test('an x-client-cert HEADER cannot override the body identity → 401', async () => {
+    const ctx = await hostCtx('alice')
+    const rogueCa = await makeP256Ca('rogue-CA')
+    const now = Date.now()
+    const rogue = await mintLeaf(ctx, new Date(now - 9 * DAY_MS), new Date(now - 8 * DAY_MS), rogueCa.caSigner)
+    const app = appWith(hostDeps(ctx, { hostCaAnchorsDer: [ctx.ca.caDer] }))
+    await app.ready()
+    const res = await app.inject({
+      method: 'POST',
+      url: '/recover',
+      headers: { 'x-client-cert': certHeader(ctx.currentCertDer) },
+      payload: { cert: b64(rogue), csr: b64Csr(ctx.csr) },
+    })
+    expect(res.statusCode).toBe(401)
+  })
+})
--- a/deploy/nginx/enroll-recover-location.md
+++ b/deploy/nginx/enroll-recover-location.md
@@ -0,0 +1,93 @@
+# Enroll vhost addition — `/recover` (expired-leaf recovery)
+
+One `location` block to **merge into the existing** enroll vhost on the VPS
+(`/etc/nginx/conf.d/enroll.conf`, the `127.0.0.1:8471` server). No new server, no new SNI route, no
+DNS work.
+
+> **This is a MERGE, not a file to ship.** The enroll vhost also carries `/enroll`, `/device/enroll`,
+> `/auth/login`, `/crl/`, `/renew` and `/device/:id/renew` — do not replace it.
+
+## Why the route exists
+
+`POST /renew` is mTLS-authenticated by the very leaf it renews, so once that leaf lapses the host can
+never renew it and the tunnel stays down until an operator re-pairs. That is not hypothetical: a
+laptop slept through its 8h renewal window, its 24h leaf expired, and the agent then logged
+`client certificate has expired; renew before dialling` 6380 times over 8 days without recovering.
+
+## Why it cannot be fixed on `/renew` itself
+
+**nginx will not forward an expired client certificate, under any `ssl_verify_client` mode.**
+
+- `optional` → nginx answers a bare `400 The SSL certificate error` as soon as verification fails.
+  The request never reaches the `location`, so no `if ($ssl_client_verify …)` can rescue it.
+- `optional_no_ca` → does **not** help either. It only tolerates *chain* failures; see nginx's
+  `ngx_ssl_verify_error_optional()`, which covers `DEPTH_ZERO_SELF_SIGNED_CERT`,
+  `SELF_SIGNED_CERT_IN_CHAIN`, `UNABLE_TO_GET_ISSUER_CERT_LOCALLY` and
+  `UNABLE_TO_VERIFY_LEAF_SIGNATURE` — and **not** `X509_V_ERR_CERT_HAS_EXPIRED`.
+- `ssl_verify_client` is a `server`-level directive, so it cannot be relaxed per-location anyway.
+
+So recovery drops mTLS: `/recover` takes **no client certificate**, and the lapsed cert travels in
+the request body instead.
+
+## Why that is still authenticated
+
+A certificate is public, so the body alone proves nothing — possession of the **private key** does,
+and it is still proven end to end:
+
+- the accompanying CSR is **self-signed by that key**, and the host signer's delegated gate enforces
+  CSR proof-of-possession plus `CSR key == registered key` (`control-plane/src/ca/csr.ts`
+  `verifyCsrPoP`);
+- `control-plane/src/api/renew.ts` runs the *same* trust pipeline as `/renew` — real X.509 path
+  validation to the frp-client-CA anchors, SPIFFE SAN parse, `notBefore`, and a registry lookup
+  requiring an `active`, account-consistent host — differing **only** in a bounded overrun allowance
+  on `notAfter` (`DEFAULT_EXPIRED_RENEW_GRACE_MS`, 30 days).
+
+Worst case for a replayed cert without the key: the attacker receives a certificate they cannot
+authenticate with. Revocation still bites, via registry status.
+
+## The block to add
+
+```nginx
+    # Expired-leaf recovery: NO client cert (see enroll-recover-location.md). The control-plane is
+    # the sole verifier; strip any client-supplied cert header so only the body can speak.
+    location = /recover {
+        limit_req zone=renew_recover burst=5 nodelay;
+        proxy_pass http://127.0.0.1:8080;
+        proxy_http_version 1.1;
+        proxy_set_header Host $host;
+        proxy_set_header x-client-cert "";
+        proxy_read_timeout 60s;
+    }
+```
+
+And once, in the `http` context (top of `enroll.conf` is fine) — the route is reachable
+pre-authentication and costs the control-plane an X.509 path validation, so bound it. The
+control-plane additionally rate-limits per identity (`createRenewRateLimiter`, 30/hour):
+
+```nginx
+limit_req_zone $binary_remote_addr zone=renew_recover:1m rate=10r/m;
+```
+
+## Deploy gate
+
+```bash
+cp /etc/nginx/conf.d/enroll.conf{,.bak.$(date +%s)}   # snapshot first
+# ...merge the block above...
+nginx -t && systemctl restart nginx                   # NEVER reload on a failed -t
+```
+
+`restart`, not `reload`: a graceful reload has been observed keeping old workers alive for seconds,
+which makes post-deploy verification race the change.
+
+## Verify
+
+```bash
+# no cert needed — an in-grace expired leaf is re-issued
+curl -sS --resolve enroll.terminal.yaojia.wang:443:<vps> \
+  -X POST -H 'content-type: application/json' \
+  -d "{\"cert\":\"$(base64 -w0 expired.cert.pem)\",\"csr\":\"$(base64 -w0 new.csr.der)\"}" \
+  https://enroll.terminal.yaojia.wang/recover        # → 201 {cert,caChain,notAfter}
+
+# a forged self-signed cert with a correct-looking SPIFFE SAN must still be refused
+# → 401   (this is the load-bearing check; nginx is no longer validating the chain here)
+```
--- a/deploy/nginx/recover-mtls.conf
+++ b/deploy/nginx/recover-mtls.conf
@@ -1,65 +0,0 @@
-# recover-mtls.conf — nginx :8472 RECOVERY vhost: re-issue a leaf that has ALREADY EXPIRED.
-#
-# Install target: /etc/nginx/conf.d/recover-mtls.conf
-# SNI route to merge into the stream map (see stream-sni-additions.md):
-#     recover.terminal.yaojia.wang  127.0.0.1:8472;
-#
-# ── WHY THIS EXISTS ───────────────────────────────────────────────────────────────────────────────
-# `POST /renew` is authenticated by mTLS with the very leaf it renews. Once that leaf lapses the host
-# can no longer renew it, so the tunnel stays down until an operator re-pairs by hand. That is not
-# hypothetical: a laptop slept through its renewal window, the leaf expired, and the agent then
-# logged `client certificate has expired; renew before dialling` 6380 times over 8 days without ever
-# recovering.
-#
-# The enroll vhost cannot host the fix. It runs `ssl_verify_client optional`, and nginx answers a
-# bare `400 Bad Request` the moment a PRESENTED client cert fails verification — an expired leaf
-# never reaches the `location`, so it can never be forwarded to the control-plane. `ssl_verify_client`
-# is a server-level directive and cannot be relaxed per-location, hence a separate server block.
-#
-# ── THE TRADE (read before changing anything here) ────────────────────────────────────────────────
-# This server runs `optional_no_ca`: nginx forwards the presented cert WITHOUT validating its chain.
-# The control-plane is therefore the SOLE and FULL verifier on this path. `api/renew.ts` does, in
-# order: real X.509 path validation to the frp-client-CA anchors (`assertPresentedCertTrusted` →
-# relay-auth `verifyChain`), SPIFFE SAN parse, `notBefore` check (NEVER graced), `notAfter` + bounded
-# grace (`DEFAULT_EXPIRED_RENEW_GRACE_MS`, 30d), then a registry lookup requiring an `active`,
-# account-consistent host — so REVOCATION IS STILL ENFORCED, via registry status rather than the CRL.
-# Do not weaken those checks on the assumption that nginx is still gating this port. It is not.
-#
-# Blast radius is deliberately tiny: ONLY `POST /renew` is reachable; every other path 404s, and the
-# strict enroll vhost (:8471) is left untouched so the normal renewal path keeps its nginx-level
-# chain + CRL enforcement.
-
-# Recovery is a once-in-a-blue-moon call per host, but it is reachable pre-authentication and costs
-# the control-plane an X.509 path validation, so bound it. CP additionally rate-limits per identity.
-limit_req_zone $binary_remote_addr zone=renew_recover:1m rate=10r/m;
-
-server {
-    listen 127.0.0.1:8472 ssl;
-    server_name recover.terminal.yaojia.wang;
-
-    ssl_certificate     /etc/relay/frp-tls/fullchain.pem;   # LE wildcard *.terminal.yaojia.wang
-    ssl_certificate_key /etc/relay/frp-tls/privkey.pem;
-
-    # Ask for a client cert and forward whatever is presented — INCLUDING an expired one, which is
-    # the entire point. `ssl_client_certificate` is kept only so the CertificateRequest carries a CA
-    # hint and clients auto-select the right identity; it does NOT gate anything under optional_no_ca.
-    ssl_verify_client optional_no_ca;
-    ssl_client_certificate /etc/relay/frp-client-ca/frp-client-ca.cert.pem;
-
-    location = /renew {
-        # Under optional_no_ca `$ssl_client_verify` is `NONE` even for a good cert, so presence of the
-        # cert itself is the only thing nginx can meaningfully assert here.
-        if ($ssl_client_escaped_cert = "") { return 403; }
-
-        limit_req zone=renew_recover burst=5 nodelay;
-
-        proxy_pass http://127.0.0.1:8080;
-        proxy_http_version 1.1;
-        proxy_set_header Host $host;
-        proxy_set_header x-client-cert $ssl_client_escaped_cert;
-        proxy_read_timeout 60s;
-    }
-
-    # Everything else — including /enroll, /device/*, /auth/login — stays on the strict vhost.
-    location / { return 404; }
-}
--- a/deploy/nginx/stream-sni-additions.md
+++ b/deploy/nginx/stream-sni-additions.md
@@ -17,18 +17,6 @@ frp.terminal.yaojia.wang  127.0.0.1:7000;   # frps control channel (TLS passthro
 *.terminal.yaojia.wang    127.0.0.1:8470;   # nginx :8470 TLS-term + device-CA mTLS (frp-mtls.conf)
 ```

-### Later addition — expired-leaf recovery (recover-mtls.conf)
-
-```nginx
-recover.terminal.yaojia.wang  127.0.0.1:8472;   # expired-leaf re-issue (recover-mtls.conf)
-```
-
-**Order IS load-bearing for this one**: it must sit ABOVE the `*.terminal.yaojia.wang` wildcard, the
-same way `enroll.terminal.yaojia.wang` does. `hostnames` gives exact matches priority over wildcards
-in nginx's `map`, so a correctly-placed line wins regardless — but keep the exact-match lines grouped
-above the wildcard so a future editor cannot mis-read the intent. No DNS work is needed: the zone is
-already served by the wildcard record `*.terminal.yaojia.wang → <vps>`.
-
 ## Coexistence warning (do NOT retype the existing lines)

 The existing `map` body already contains — and MUST be preserved **verbatim**:
				`@@ -0,0 +1 @@`
				`/Users/yiukai/Documents/git/web-terminal/agent/node_modules`