fix: harden website blocklist — default off, TTL cache, fail-open, guarded imports

- Default enabled: false (zero overhead when not configured)
- Fast path: cached disabled state skips all work immediately
- TTL cache (30s) for parsed policy — avoids re-reading config.yaml
  on every URL check
- Missing shared files warn + skip instead of crashing all web tools
- Lazy yaml import — missing PyYAML doesn't break browser toolset
- Guarded browser_tool import — fail-open lambda fallback
- check_website_access never raises for default path (fail-open with
  warning log); only raises with explicit config_path (test mode)
- Simplified enforcement code in web_tools/browser_tool — no more
  try/except wrappers since errors are handled internally

tools/browser_tool.py

@@ -65,7 +65,11 @@ import requests
 from typing import Dict, Any, Optional, List
 from pathlib import Path
 from agent.auxiliary_client import call_llm
-from tools.website_policy import check_website_access
+
+try:
+    from tools.website_policy import check_website_access
+except Exception:
+    check_website_access = lambda url: None  # noqa: E731 — fail-open if policy module unavailable
 from tools.browser_providers.base import CloudBrowserProvider
 from tools.browser_providers.browserbase import BrowserbaseProvider
 from tools.browser_providers.browser_use import BrowserUseProvider
@@ -903,12 +907,8 @@ def browser_navigate(url: str, task_id: Optional[str] = None) -> str:
         JSON string with navigation result (includes stealth features info on first nav)
     """
     # Website policy check — block before navigating
-    try:
-        blocked = check_website_access(url)
-    except Exception as _policy_err:
-        return json.dumps({"success": False, "error": f"Website policy error: {_policy_err}"})
+    blocked = check_website_access(url)
     if blocked:
-        logger.info("Blocked browser_navigate to %s by rule %s", blocked["host"], blocked["rule"])
         return json.dumps({
             "success": False,
             "error": blocked["message"],