Sales Invoice Flow Overview
===========================

Goal
----

The Sales Invoice flow adds a specialized invoice flow for e-commerce and
jurisdiction-aware tax handling while keeping upstream ``django-ledger`` models
upgrade-safe.

Design
------

The flow does not modify ``django_ledger.InvoiceModel`` schema. Instead, it
extends invoice behavior using related models:

* ``SalesInvoiceProfile``: one-to-one sales profile linked to ``InvoiceModel``.
* ``SalesInvoiceTaxComponent``: aggregated tax totals by tax type.
* ``SalesInvoiceLineSummary``: line-level computed tax snapshot.
* ``SalesInvoiceLineTaxComponent``: per-line component details (GST/PST/HST/US).
* ``SalesTaxPreset``: country/region tax presets (seeded for Canada).

Routes
------

The flow is available under:

* ``/ledger/sales-invoices/<entity-slug>/``
* ``/ledger/sales-invoices/<entity-slug>/create/``
* ``/ledger/sales-invoices/<entity-slug>/<sales_invoice_pk>/``
* ``/ledger/sales-invoices/<entity-slug>/<sales_invoice_pk>/edit/``

Compatibility with upstream updates
-----------------------------------

Because the flow stores custom metadata in ``accounting`` app models and
does not fork ``django-ledger`` source code, pulling upstream package updates is
low-risk.