The official Databricks Apps quickstart puts everything into a single app.py. Fine for a demo โ painful once the app grows past ~500 lines.
Problems with the single-file pattern:
- Merge conflicts on every PR
- UI, logic, and SDK calls coupled โ no unit tests
- Unreadable diffs in code review
- AI assistants (Cursor, Claude) re-parse the whole file every prompt โ high token cost
