That’s a good point. The output generated by Guild about dependency resolution errors will not appear in run logs but is shown on the console. In this case you need to scan console output for these messages. Again, Guild only knows when a trial fails by its exit code. It doesn’t otherwise know why. That information should appear in the output. If the script doesn’t show an error message, there’s no information to go off of.
config is quite different from file. When you use config, you specify a JSON or YAML file that Guild uses to generate a new file containing flag values. Guild does not support toml format, so the error message is accurate.
This is covered in more detail here: Dependencies.