frappe-impl-customapp

To build a custom Frappe app reliably, use `bench new-app` for scaffolding, configure `pyproject.toml` dependencies correctly by excluding frappe/erpnext, and align `modules.txt` with your directory structure to ensure end-to-end functionality on fresh sites.

Configuring fixtures in a Frappe custom app requires setting controlled export filters in `hooks.py` to ensure only your app’s specific configuration is exported, preventing production failures caused by overwriting the wrong data on fresh sites.

Frappe v14 and v15 use `doc_events` for hooks, while v16 introduces `extend_doctype_class` extension patterns; safe data migrations across these versions require correct patch timing and guard clauses for deterministic behavior.

Safe data migrations in Frappe require deterministic migration behavior using batching, commit strategies, and schema guards, alongside correct patch timing and guard clauses to prevent broken updates during the migrate and build lifecycle.

Frappe and erpnext must be excluded from PyPI dependencies in `pyproject.toml` because the bench environment already provides them; including them causes dependency conflicts and breaks app installation on fresh sites.

Structuring modules and DocTypes in a new Frappe app involves deciding module organization, creating DocType controllers and files, and keeping `modules.txt` strictly aligned with your directory structure to prevent packaging and migration errors.