security: agent-shell WS tokens and dependency audit fixes (#409)

Replace spoofable Host/Origin WebSocket auth with short-lived bootstrap
tokens minted over the existing local-operator HTTP path. Docker/browser
shell sessions prefetch a token before connecting; loopback peers remain
unchanged.

Also bump backend ws to 8.21.0 and refresh frontend lockfile to clear
npm audit findings (dev toolchain only for frontend).

Fixes #405, #406, #407

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/services/agent_shell_ws_token.py

@@ -0,0 +1,52 @@
+"""Short-lived, single-use WebSocket bootstrap tokens for the agent shell."""
+
+from __future__ import annotations
+
+import secrets
+import time
+from threading import Lock
+
+_TOKEN_TTL_SECONDS = 60.0
+_MAX_ACTIVE_TOKENS = 256
+
+_store: dict[str, float] = {}
+_lock = Lock()
+
+
+def _purge_expired(*, force: bool = False) -> None:
+    now = time.time()
+    with _lock:
+        expired = [token for token, expires in _store.items() if expires <= now]
+        for token in expired:
+            _store.pop(token, None)
+        if force and len(_store) > _MAX_ACTIVE_TOKENS:
+            for token in list(_store.keys())[: len(_store) - _MAX_ACTIVE_TOKENS]:
+                _store.pop(token, None)
+
+
+def mint_agent_shell_ws_token() -> tuple[str, int]:
+    """Return (token, expires_in_seconds)."""
+    _purge_expired()
+    token = secrets.token_urlsafe(32)
+    expires_at = time.time() + _TOKEN_TTL_SECONDS
+    with _lock:
+        if len(_store) >= _MAX_ACTIVE_TOKENS:
+            _purge_expired(force=True)
+        _store[token] = expires_at
+    return token, int(_TOKEN_TTL_SECONDS)
+
+
+def consume_agent_shell_ws_token(token: str) -> bool:
+    """Validate and burn a one-time token. Returns True when accepted."""
+    cleaned = str(token or "").strip()
+    if not cleaned:
+        return False
+    now = time.time()
+    with _lock:
+        expires_at = _store.pop(cleaned, None)
+    return expires_at is not None and expires_at > now
+
+
+def reset_agent_shell_ws_tokens_for_tests() -> None:
+    with _lock:
+        _store.clear()