fix: tighten small-model audit guardrails

docs/gateway/security.md

@@ -177,6 +177,7 @@ Recommendations:
 - **Use the latest generation, best-tier model** for any bot that can run tools or touch files/networks.
 - **Avoid weaker tiers** (for example, Sonnet or Haiku) for tool-enabled agents or untrusted inboxes.
 - If you must use a smaller model, **reduce blast radius** (read-only tools, strong sandboxing, minimal filesystem access, strict allowlists).
+- When running small models, **enable sandboxing for all sessions** and **disable web_search/web_fetch/browser** unless inputs are tightly controlled.
 
 ## Reasoning & verbose output in groups