fix: don't send OpenRouter-specific provider preferences to Nous Portal

Two bugs in _build_api_kwargs that broke Nous Portal:

1. Provider preferences (only, ignore, order, sort) are OpenRouter-
   specific routing features. They were being sent in extra_body to ALL
   providers, including Nous Portal. When the config had
   providers_only=['google-vertex'], Nous Portal returned 404 'Inference
   host not found' because it doesn't have a google-vertex backend.

   Fix: Only include provider preferences when _is_openrouter is True.

2. Reasoning config with enabled=false was being sent to Nous Portal,
   which requires reasoning and returns 400 'Reasoning is mandatory for
   this endpoint and cannot be disabled.'

   Fix: Omit the reasoning parameter for Nous when enabled=false.

Root cause found via HERMES_DUMP_REQUESTS=1 which showed the exact
request payload being sent to Nous Portal's inference API.

run_agent.py

@@ -2392,16 +2392,24 @@ class AIAgent:
 
         extra_body = {}
 
-        if provider_preferences:
-            extra_body["provider"] = provider_preferences
-
         _is_openrouter = "openrouter" in self.base_url.lower()
+
+        # Provider preferences (only, ignore, order, sort) are OpenRouter-
+        # specific — don't send them to other providers (Nous, Codex, etc.)
+        if provider_preferences and _is_openrouter:
+            extra_body["provider"] = provider_preferences
         _is_nous = "nousresearch" in self.base_url.lower()
 
         _is_mistral = "api.mistral.ai" in self.base_url.lower()
         if (_is_openrouter or _is_nous) and not _is_mistral:
             if self.reasoning_config is not None:
-                extra_body["reasoning"] = self.reasoning_config
+                rc = dict(self.reasoning_config)
+                # Nous Portal requires reasoning enabled — don't send
+                # enabled=false to it (would cause 400).
+                if _is_nous and rc.get("enabled") is False:
+                    pass  # omit reasoning entirely for Nous when disabled
+                else:
+                    extra_body["reasoning"] = rc
             else:
                 extra_body["reasoning"] = {
                     "enabled": True,