Local command execution via unrestricted input_model exec

Code injection in Defog Introspect 0.1.0 through 0.1.4 allows local users to execute arbitrary commands through the custom-tools test endpoint. The test_custom_tool handler passes the complete input_model string to Python exec(), allowing imports and built-ins to escape its BaseModel-and-Field namespace. Low-privileged local access is required; successful injection runs with the backend service's privileges and can read, modify, or interrupt its data and processes.