Worker: interactive terminal WebSocket bridge (PTY in workspace container)

- attachTerminalServer() upgrades /jobs/:id/terminal WS connections, verifying a
  short-lived job-scoped HMAC token (verifyTerminalToken) so the browser never
  holds the worker secret
- Bridges the socket to a bash PTY via dockerode exec (Tty) in a persistent
  per-job shell container (spoon-agent-term-<id>) mounting the workspace; binary
  frames = stdin, JSON text frames = resize; idle containers reaped after 30m
- New env: SPOON_AGENT_TERMINAL_IMAGE/SECRET/IDLE_MS (secret falls back to the
  shared worker internal token)

apps/agent-worker/src/terminal-token.ts

@@ -0,0 +1,29 @@
+import { createHmac, timingSafeEqual } from 'node:crypto';
+
+// Short-lived, job-scoped token authorizing a browser terminal connection.
+// Minted server-side by the Next app (which has verified job ownership) and
+// verified here so the browser never sees the shared worker secret. Format:
+//   `${expiresAtMs}.${jobId}.${hmacSha256Hex}`
+const signature = (payload: string, secret: string) =>
+  createHmac('sha256', secret).update(payload).digest('hex');
+
+export const verifyTerminalToken = (
+  token: string,
+  jobId: string,
+  secret: string,
+): boolean => {
+  if (!token || !secret) return false;
+  const parts = token.split('.');
+  if (parts.length !== 3) return false;
+  const [expRaw, tokenJobId, provided] = parts;
+  if (tokenJobId !== jobId) return false;
+  const exp = Number.parseInt(expRaw ?? '', 10);
+  if (!Number.isFinite(exp) || Date.now() > exp) return false;
+  const expected = signature(`${expRaw}.${tokenJobId}`, secret);
+  const providedBuf = Buffer.from(provided ?? '', 'hex');
+  const expectedBuf = Buffer.from(expected, 'hex');
+  return (
+    providedBuf.length === expectedBuf.length &&
+    timingSafeEqual(providedBuf, expectedBuf)
+  );
+};