feat(relay): rendezvous-relay service — 7 packages + plans (contracts/transport/agent/control-plane/e2e/auth/web)

Multi-tenant reverse-tunnel service ("ngrok for Claude Code" with E2E): a
host-agent dials OUT to an operator-run relay; external devices reach the host
THROUGH the relay, routed by per-tenant subdomain, forwarding ciphertext only
(the relay never sees plaintext). Lets a customer reach their own self-hosted
web-terminal from anywhere with zero networking setup.

Packages — all tsc-strict + vitest green (656 tests), cross-package integration verified:
- relay-contracts: frozen shared contracts (mux frame codec, data model,
  capability token, E2E envelope, pairing) — the src/types.ts analog
- term-relay:   native WS mux + stateless data plane (subdomain routing, ciphertext forward)
- agent:        host-agent (pairing, per-host Ed25519 + mTLS dial-out, forwards to 127.0.0.1:3000)
- control-plane: accounts/hosts registry, pairing-code flow, routing table, provisioning
- relay-e2e:    browser<->agent E2E (X25519 ECDH through relay, AEAD, anti-replay, recoverable replay key)
- relay-auth:   Passkey/WebAuthn, capability tokens, per-host certs, deny-by-default tenant isolation
- relay-web:    browser login + Web Crypto E2E + client-side preview rendering

Security invariants INV1-15 enforced; cross-tenant isolation CI tripwire live
(.github/workflows/relay-tripwire.yml). Design + implementation-level plans in
docs/PLAN_RELAY_*.md and docs/EXPLORE_RELAY_SERVICE.md.

NOTE: generated autonomously per the reviewed plans. The security-critical
packages (relay-e2e, relay-auth) REQUIRE expert security audit before any real
deployment — passing tests prove self-consistency, not resistance to attackers.
Base app (src/, public/) unchanged; concurrent desktop work left uncommitted.

control-plane/src/boot/ca-wiring.ts

@@ -0,0 +1,75 @@
+/**
+ * T15 — CA-key / secret-manager bootstrap + KMS-signer factory (§3.1). The intermediate
+ * leaf-signing key is a non-exportable KMS/HSM key: signing is a `sign()` CALL, the raw private
+ * key is NEVER loaded into control-plane memory. `buildCaSigner` FAILS FAST at startup (INV9) if
+ * the key ref is unresolvable OR its policy does not restrict `sign` to the control-plane
+ * service principal. Both T8 `signHostLeaf` and T15 `renewHostLeaf` call this shared primitive —
+ * neither loads a raw key.
+ */
+import { createPublicKey } from 'node:crypto'
+import type { ControlPlaneEnv } from '../env.js'
+import { ed25519Sign, generateEd25519, type KeyObject } from '../util/crypto.js'
+
+/** Wraps KMS `sign()`; no raw key ever crosses this boundary. */
+export interface CaSigner {
+  sign(tbsCert: Uint8Array): Promise<Uint8Array>
+  /** Public verifying key of the CA (for tests / chain assembly). */
+  readonly publicKeyRaw: Uint8Array
+}
+
+/**
+ * KMS resolver seam. Production resolves a real KMS/HSM key handle + policy; tests inject a fake.
+ * A resolver returns `{ canSign, policyRestrictedToServicePrincipal }` for the given ref, or throws
+ * if the ref cannot be resolved at all.
+ */
+export interface KmsResolver {
+  resolve(keyRef: string): Promise<{
+    readonly signer: CaSigner
+    readonly policyRestrictedToServicePrincipal: boolean
+  }>
+}
+
+/**
+ * Build the CA signer for the configured intermediate KMS key. Fail-fast (INV9, §3.1):
+ *  - throws if the resolver cannot resolve the ref;
+ *  - throws if the KMS key policy is broader than the control-plane service principal.
+ */
+export async function buildCaSigner(env: ControlPlaneEnv, resolver: KmsResolver): Promise<CaSigner> {
+  let resolved
+  try {
+    resolved = await resolver.resolve(env.caIntermediateKmsKeyRef)
+  } catch (err: unknown) {
+    // Never log the ref VALUE — only that resolution failed (INV9).
+    throw new Error(
+      `CA intermediate KMS key could not be resolved: ${err instanceof Error ? err.message : 'unknown'}`,
+    )
+  }
+  if (!resolved.policyRestrictedToServicePrincipal) {
+    throw new Error(
+      'CA intermediate KMS key policy is broader than the control-plane service principal (§3.1) — refusing to boot',
+    )
+  }
+  return resolved.signer
+}
+
+/**
+ * In-process Ed25519 CA signer — TEST/DEV ONLY (clearly NOT a KMS; the plan mandates a real
+ * non-exportable KMS key in production, §3.1). Exposes the same `sign()` surface so callers are
+ * KMS-shaped and never touch a raw key path themselves.
+ */
+export function inProcessCaSigner(privateKey?: KeyObject): CaSigner {
+  const key = privateKey ?? generateEd25519().privateKey
+  const pub = derivePublicRaw(key)
+  return {
+    publicKeyRaw: pub,
+    async sign(tbsCert) {
+      return ed25519Sign(key, tbsCert)
+    },
+  }
+}
+
+function derivePublicRaw(privateKey: KeyObject): Uint8Array {
+  // Recover the raw 32-byte Ed25519 public key from the private KeyObject.
+  const spki = createPublicKey(privateKey).export({ format: 'der', type: 'spki' }) as Buffer
+  return new Uint8Array(spki.subarray(spki.length - 32))
+}