Fail fast on invalid config files

nanobot/config/loader.py

@@ -7,7 +7,6 @@ from pathlib import Path
 from typing import Any
 
 import pydantic
-from loguru import logger
 from pydantic import BaseModel
 
 from nanobot.config.schema import Config, _resolve_tool_config_refs
@@ -55,8 +54,7 @@ def load_config(config_path: Path | None = None) -> Config:
             data = _migrate_config(data)
             config = Config.model_validate(data)
         except (json.JSONDecodeError, ValueError, pydantic.ValidationError) as e:
-            logger.warning("Failed to load config from {}: {}", path, e)
-            logger.warning("Using default configuration.")
+            raise ValueError(f"Failed to load config from {path}: {e}") from e
 
     _apply_ssrf_whitelist(config)
     return config