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.

relay-e2e/src/errors.ts

@@ -0,0 +1,59 @@
+/**
+ * T0 — typed error classes for relay-e2e (PLAN_RELAY_E2E §3 T0).
+ *
+ * Every error subclasses {@link E2EError} and carries a stable, greppable `code`. Per INV9,
+ * a thrown message MUST NEVER embed key/nonce/plaintext material — callers surface the code,
+ * not secret bytes. No `console` here; the caller decides how to handle.
+ */
+
+/** Base class for all relay-e2e crypto errors. */
+export class E2EError extends Error {
+  readonly code: string
+  constructor(code: string, message: string) {
+    super(message)
+    this.name = new.target.name
+    this.code = code
+  }
+}
+
+/** Pinned enroll_fpr / registry pubkey disagreement ⇒ MITM abort (§4d). */
+export class FingerprintMismatchError extends E2EError {
+  constructor(message = 'host fingerprint mismatch') {
+    super('E2E_FINGERPRINT_MISMATCH', message)
+  }
+}
+
+/** AEAD tag verification failed ⇒ drop the frame and tear the session down. */
+export class AeadOpenError extends E2EError {
+  constructor(message = 'AEAD authentication failed') {
+    super('E2E_AEAD_OPEN', message)
+  }
+}
+
+/** Sequence number non-monotonic / duplicate / reordered / gapped (INV13). */
+export class ReplayError extends E2EError {
+  constructor(message = 'sequence replay/reorder rejected') {
+    super('E2E_REPLAY', message)
+  }
+}
+
+/** Illegal handshake transition, wrong phase, or unusable negotiation. */
+export class HandshakeStateError extends E2EError {
+  constructor(message = 'illegal handshake state transition') {
+    super('E2E_HANDSHAKE_STATE', message)
+  }
+}
+
+/** Malformed wire bytes / unsupported version / bad AEAD id. */
+export class EnvelopeFormatError extends E2EError {
+  constructor(message = 'malformed envelope') {
+    super('E2E_ENVELOPE_FORMAT', message)
+  }
+}
+
+/** No WebCrypto / CSPRNG available in the host environment (fail-fast boundary). */
+export class CryptoUnavailableError extends E2EError {
+  constructor(message = 'WebCrypto is unavailable in this environment') {
+    super('E2E_CRYPTO_UNAVAILABLE', message)
+  }
+}