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-web/src/terminal-view.ts

@@ -0,0 +1,124 @@
+/**
+ * T4 — mount xterm + FitAddon and drive it through an abstract `TerminalTransport`.
+ *
+ * Reproduces the base byte semantics against the SEAM (not `public/`): Enter → `\r` (0x0D, handled
+ * by xterm's own onData), `resize` as its OWN protocol frame (triggering `TIOCSWINSZ`/SIGWINCH so
+ * full-screen TUIs redraw), and `fit()` only after the container has real dimensions (calling it
+ * while `display:none` yields NaN — base Gotcha).
+ *
+ * The terminal is injected (DI seam) so tests run in jsdom without a real canvas-backed xterm; the
+ * default factory wires `@xterm/xterm` + `@xterm/addon-fit`.
+ */
+import { encodeClientMessage, decodeServerMessage } from './protocol'
+import type { TerminalTransport } from './ws-transport'
+
+/** Minimal xterm surface this view needs (keeps tests mock-able, avoids canvas in jsdom). */
+export interface TerminalLike {
+  readonly cols: number
+  readonly rows: number
+  open(container: HTMLElement): void
+  write(data: string): void
+  onData(cb: (data: string) => void): void
+  fit(): void
+  dispose(): void
+}
+
+export interface TerminalViewDeps {
+  /** Factory for the terminal; default lazily loads xterm + FitAddon. */
+  readonly createTerminal?: () => TerminalLike
+}
+
+/** True only when the element has real, non-zero layout dimensions (guards NaN fit — Gotcha). */
+function hasRealDimensions(el: HTMLElement): boolean {
+  return el.clientWidth > 0 && el.clientHeight > 0
+}
+
+async function defaultTerminal(): Promise<TerminalLike> {
+  const [{ Terminal }, { FitAddon }] = await Promise.all([
+    import('@xterm/xterm'),
+    import('@xterm/addon-fit'),
+  ])
+  const term = new Terminal({ convertEol: false })
+  const fit = new FitAddon()
+  term.loadAddon(fit)
+  return {
+    get cols() {
+      return term.cols
+    },
+    get rows() {
+      return term.rows
+    },
+    open: (container) => term.open(container),
+    write: (data) => term.write(data),
+    onData: (cb) => {
+      term.onData(cb)
+    },
+    fit: () => fit.fit(),
+    dispose: () => term.dispose(),
+  }
+}
+
+/**
+ * Mount the terminal view. Returns `{ dispose }`. When `deps.createTerminal` is omitted the real
+ * xterm is loaded asynchronously; tests always inject a mock for deterministic, synchronous setup.
+ */
+export function mountTerminalView(
+  root: HTMLElement,
+  transport: TerminalTransport,
+  deps: TerminalViewDeps = {},
+): { dispose(): void } {
+  let term: TerminalLike | null = null
+  let disposed = false
+
+  const send = (bytes: Uint8Array): void => {
+    try {
+      transport.send(bytes)
+    } catch {
+      // Socket not open / torn down — drop; onClose surfaces the reason to the UI.
+    }
+  }
+
+  const sendResize = (): void => {
+    if (!term || !hasRealDimensions(root)) return
+    term.fit()
+    send(encodeClientMessage({ type: 'resize', cols: term.cols, rows: term.rows }))
+  }
+
+  const wire = (t: TerminalLike): void => {
+    if (disposed) {
+      t.dispose()
+      return
+    }
+    term = t
+    t.open(root)
+
+    // keypress → xterm onData → transport.send (Enter → '\r' comes from xterm itself).
+    t.onData((data) => send(encodeClientMessage({ type: 'input', data })))
+
+    // incoming DATA → decode base ServerMessage → xterm.write (output only; attached/exit handled).
+    transport.onMessage((bytes) => {
+      const msg = decodeServerMessage(bytes)
+      if (msg && msg.type === 'output') t.write(msg.data)
+    })
+
+    // attach MUST be the first client message (base invariant); sessionId=null → fresh session.
+    send(encodeClientMessage({ type: 'attach', sessionId: null }))
+
+    if (hasRealDimensions(root)) sendResize()
+  }
+
+  const created = deps.createTerminal
+  if (created) {
+    wire(created())
+  } else {
+    void defaultTerminal().then(wire)
+  }
+
+  return {
+    dispose(): void {
+      disposed = true
+      if (term) term.dispose()
+      transport.close()
+    },
+  }
+}