fix(security): validate Nous Portal inference_base_url against host allowlist

The Nous Portal proxy adapter forwards minted ``agent_key`` bearer tokens
to whatever ``base_url`` ``resolve_nous_runtime_credentials()`` returns,
which is read directly from the refresh / agent-key-mint response and
persisted to ``~/.hermes/auth.json``. With no validation beyond a
trailing-slash strip, a poisoned URL (Portal-side MITM, or local write
to auth.json) gets forwarded the legitimate bearer on every subsequent
proxy request — exfiltrating the user's inference budget and opening a
response-injection channel back into the IDE / chat client.

Add ``_validate_nous_inference_url_from_network()`` in ``hermes_cli.auth``:
an https + host-allowlist check that returns None for anything outside
``inference-api.nousresearch.com``, so callers fall back to the
documented default rather than ship the bearer to an attacker.

This commit wires the validator into the proxy adapter at
``nous_portal.py``. A follow-up commit wires it into the four refresh /
mint sites in ``auth.py`` so the poisoned URL never lands in auth.json
in the first place.

The env-var override path (``NOUS_INFERENCE_BASE_URL``) bypasses
validation by design — that's the documented staging/dev escape hatch
and the env source is already trusted (the user set it themselves).

Co-authored-by: memosr <mehmet.sr35@gmail.com>

hermes_cli/auth.py

@@ -41,7 +41,7 @@ from dataclasses import dataclass, field
 from datetime import datetime, timezone
 from http.server import BaseHTTPRequestHandler, HTTPServer, ThreadingHTTPServer
 from pathlib import Path
-from typing import Any, Callable, Dict, List, Optional, Tuple
+from typing import Any, Callable, Dict, FrozenSet, List, Optional, Tuple
 from urllib.parse import parse_qs, urlencode, urlparse
 
 import httpx
@@ -1559,6 +1559,67 @@ def _optional_base_url(value: Any) -> Optional[str]:
     return cleaned if cleaned else None
 
 
+# Allowlist of hosts the Nous Portal proxy is willing to forward minted
+# bearer tokens to. The bearer is a long-lived agent_key minted by
+# portal.nousresearch.com — sending it anywhere else would leak it.
+#
+# This is consulted only for URLs coming from the NETWORK side (Portal
+# refresh / agent-key-mint responses). User-controlled env-var overrides
+# (NOUS_INFERENCE_BASE_URL) bypass validation — that's the documented
+# dev/staging escape hatch and the env source is already trusted (the
+# user set it themselves).
+_ALLOWED_NOUS_INFERENCE_HOSTS: FrozenSet[str] = frozenset({
+    "inference-api.nousresearch.com",
+})
+
+
+def _validate_nous_inference_url_from_network(url: Optional[str]) -> Optional[str]:
+    """Validate a Portal-returned inference URL against the host allowlist.
+
+    Returns ``url`` (normalised by stripping trailing slashes) if it's a
+    well-formed ``https://<allowlisted-host>/...`` URL. Returns ``None``
+    if the URL is missing, malformed, non-https, or points at an
+    unexpected host — letting the caller fall back to the configured
+    default rather than persist or forward a poisoned value.
+
+    Defense-in-depth: a compromised refresh / mint response from the
+    Portal API (MITM, malicious response injection) could otherwise
+    redirect every subsequent proxy request — bearing the user's
+    legitimately-minted agent_key — to an attacker-controlled endpoint.
+    Validating scheme + host at the source closes that loop before the
+    poisoned URL ever lands in ``auth.json``.
+
+    The env-var override path (``NOUS_INFERENCE_BASE_URL``) bypasses
+    this — env values come from the trusted OS user, not from the
+    network, and the override is documented for staging/dev use.
+
+    Co-authored-by: memosr <mehmet.sr35@gmail.com>
+    """
+    if not isinstance(url, str):
+        return None
+    cleaned = url.strip()
+    if not cleaned:
+        return None
+    try:
+        parsed = urlparse(cleaned)
+    except Exception:
+        return None
+    if parsed.scheme != "https":
+        logger.warning(
+            "nous: refusing non-https inference URL scheme %r from Portal response",
+            parsed.scheme,
+        )
+        return None
+    if parsed.hostname not in _ALLOWED_NOUS_INFERENCE_HOSTS:
+        logger.warning(
+            "nous: refusing inference URL host %r from Portal response "
+            "(not in allowlist); falling back to default",
+            parsed.hostname,
+        )
+        return None
+    return cleaned.rstrip("/")
+
+
 def _decode_jwt_claims(token: Any) -> Dict[str, Any]:
     if not isinstance(token, str) or token.count(".") != 2:
         return {}