Tidy up the validation code. The warning message should point out that the app folder is missing or that the object is missing or that the step is missing etc. Regardless of what's missing, the generate code will create everything.
Move qualified name derivation into generate method so that the quickfix code doesn't need to figure that out.
As part of validation, warn that the app, obj, section, field doesn't exist. Make it a fast validation.
For the quickfix, call the creation code used by the build all feature.