fix(xai-proxy): handle 429 rate-limit responses in proxy retry path

get_retry_credential only triggered on 401; a 429 Too Many Requests from
xAI was silently streamed back with no key rotation or back-off signal.

- server.py: widen retry gate from == 401 to in {401, 429}
- xai.py: on 429, skip token refresh and call mark_exhausted_and_rotate
  to stamp the 1-hour cooldown on the rate-limited key and return the
  next available credential. Returns None if pool is exhausted.

hermes_cli/proxy/adapters/xai.py

@@ -79,7 +79,7 @@ class XAIGrokAdapter(UpstreamAdapter):
         failed_credential: UpstreamCredential,
         status_code: int,
     ) -> Optional[UpstreamCredential]:
-        if status_code != 401:
+        if status_code not in {401, 429}:
             return None
 
         with self._lock:
@@ -87,16 +87,25 @@ class XAIGrokAdapter(UpstreamAdapter):
             if pool is None:
                 return None
 
-            refreshed = pool.try_refresh_current()
-            if refreshed is None:
+            if status_code == 429:
+                # Mark the rate-limited key with its 1-hour cooldown and rotate
+                # to the next available credential. Returns None when the pool
+                # has no other key to offer — the 429 will flow back to the client.
                 refreshed = pool.mark_exhausted_and_rotate(status_code=status_code)
+            else:
+                refreshed = pool.try_refresh_current()
+                if refreshed is None:
+                    refreshed = pool.mark_exhausted_and_rotate(status_code=status_code)
             if refreshed is None:
                 return None
 
             retry_cred = self._credential_from_entry(refreshed)
             if retry_cred.bearer == failed_credential.bearer:
                 return None
-            logger.info("proxy: xAI upstream rejected bearer; retrying with refreshed pool credential")
+            logger.info(
+                "proxy: xAI upstream returned %s; retrying with rotated pool credential",
+                status_code,
+            )
             return retry_cred
 
     def _load_pool(self) -> Optional[CredentialPool]:

hermes_cli/proxy/server.py

@@ -206,7 +206,7 @@ def create_app(adapter: UpstreamAdapter) -> "web.Application":
             return session_or_response
         session = session_or_response
 
-        if upstream_resp.status == 401:
+        if upstream_resp.status in {401, 429}:
             try:
                 retry_cred = adapter.get_retry_credential(
                     failed_credential=cred,