Tools, don't merge custom with existing defaults (#367)

* Tools, don't merge custom with existing defaults

* Use ternary operator instead of if else block

Author: lukehinds

deepfabric/tools/loader.py

@@ -110,17 +110,13 @@ def get_available_tools(
 
     Args:
         available_tool_names: List of tool names to include (None means all)
-        custom_registry: Custom tool registry to merge with defaults
+        custom_registry: Custom tool registry (if provided, REPLACES defaults entirely)
 
     Returns:
         ToolRegistry with available tools
     """
-    # Start with defaults
-    if custom_registry is not None:
-        # Merge custom tools with defaults (custom tools override defaults)
-        registry = merge_tool_registries(DEFAULT_TOOL_REGISTRY, custom_registry)
-    else:
-        registry = DEFAULT_TOOL_REGISTRY
+    # Use custom tools if provided (replaces defaults), otherwise use defaults
+    registry = custom_registry if custom_registry is not None else DEFAULT_TOOL_REGISTRY
 
     # Filter by available tool names if specified
     if available_tool_names: