# TANRAIL ONE — Phase 3.2.3 Implementation Report

## Overview
Phase 3.2.3 (Core Sales Engine) has been fully implemented and tested according to the business-agnostic architectural mandate. It provides a robust transaction engine that securely interfaces with the Phase 3.2 Inventory Core without violating module boundaries or business logic.

## Files Created & Modified

### Migrations
- `[NEW] 2026_09_04_xxxxxx_add_default_sales_location_id_to_branches_table.php`
- `[NEW] 2026_09_04_xxxxxx_create_sales_tables.php` (orders, order_lines, payments)

### Models
- `[NEW] Order.php` (Enforces BusinessUnitScope)
- `[NEW] OrderLine.php` (Enforces state-based immutability)
- `[NEW] Payment.php` (Enforces append-only immutability)
- `[MODIFIED] Branch.php` (Added `default_sales_location_id` relation & fillable)

### Enums
- `[NEW] OrderStatus.php` (DRAFT, CONFIRMED, FULFILLED, COMPLETED, CANCELLED)
- `[MODIFIED/REUSED] PaymentMethod.php` (CASH, CARD, BANK_TRANSFER, MOBILE_MONEY)

### Services & Policies
- `[NEW] OrderService.php` (Core state machine, BU isolation, pessimistic locking)
- `[NEW] OrderPolicy.php` (Tripartite Authorization mapping)

### Events & Listeners
- `[NEW] OrderConfirmed.php` -> `DeductInventoryListener.php`
- `[NEW] OrderCancelled.php` -> `RestoreInventoryListener.php`
- `[MODIFIED] AppServiceProvider.php` (Registered Policies & Events)

### Tests
- `[NEW] Phase323SalesEngineTest.php` (24 rigorous security and lifecycle tests)

## Security Controls Implemented
1. **Context Boundary**: The `Order` model uses `BusinessUnitScope` dynamically loaded from the Active Context.
2. **Cross-BU Protection**: `OrderService::addItem()` explicitly asserts `$item->business_unit_id === $order->branch->business_unit_id`.
3. **Pessimistic Locking**: Concurrent confirmations are blocked using `lockForUpdate()` within Database Transactions.
4. **Historical Immutability**: `OrderLine` prices/taxes freeze on confirmation; `Payment` records are permanently append-only via Model Observers.

## Inventory Integration
Sales and Inventory are physically decoupled but transactionally synchronized. `OrderConfirmed` triggers a synchronous listener that calls `InventoryService::issue()`. If negative stock is detected, the resulting Exception safely rolls back the entire Sales transaction, guaranteeing mathematical integrity. 

## Future Expansion Validation
The Core Sales engine operates entirely on `Branch`, `Customer`, and `Item` concepts. A future Restaurant Extension merely needs to map a `Table` to an `Order_ID`. A future Catering Extension maps an `Event` to an `Order_ID`. Core Sales requires exactly ZERO modifications to support this.

## Known Risks / Unresolved Decisions
None. The human decision to add `default_sales_location_id` to the `Branch` model elegantly resolved the Inventory deduction source ambiguity.