feat: add core POS module — transactions, discounts, drawer, tax

Phase 3a backend API for point-of-sale. Includes:

Schema (packages/backend/src/db/schema/pos.ts):
- pgEnums: transaction_type, transaction_status, payment_method,
  discount_type, discount_applies_to, drawer_status
- Tables: transaction, transaction_line_item, discount,
  discount_audit, drawer_session
- Transaction links to accounts, repair_tickets, repair_batches
- Line items link to products and inventory_units

Tax system:
- tax_rate + service_tax_rate columns on location
- tax_category enum (goods/service/exempt) on product
- Tax resolves per line item: goods→tax_rate, service→service_tax_rate,
  exempt→0. Repair line items map: part→goods, labor→service
- GET /tax/lookup/:zip stubbed for future API integration (TAX_API_KEY)

Services (export const pattern, matching existing codebase):
- TransactionService: create, addLineItem, removeLineItem, applyDiscount,
  recalculateTotals, complete (decrements inventory), void, getReceipt
- DiscountService: CRUD + listAll for dropdowns
- DrawerService: open/close with expected balance + over/short calc
- TaxService: getRateForLocation (by tax category), calculateTax

Routes:
- POST/GET /transactions, GET /transactions/:id, GET /transactions/:id/receipt
- POST /transactions/:id/line-items, DELETE /transactions/:id/line-items/:id
- POST /transactions/:id/discounts, /complete, /void
- POST /drawer/open, POST /drawer/:id/close, GET /drawer/current, GET /drawer
- CRUD /discounts + GET /discounts/all
- GET /products/lookup/upc/:upc (barcode scanner support)

All routes gated by pos.view/pos.edit/pos.admin + withModule('pos').
POS module already seeded in migration 0026.

Still needed: bun install, drizzle-kit generate + migrate, tests, lint.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/backend/src/db/index.ts

@@ -2,3 +2,4 @@ export * from './schema/stores.js'
 export * from './schema/users.js'
 export * from './schema/accounts.js'
 export * from './schema/inventory.js'
+export * from './schema/pos.js'

packages/backend/src/db/schema/inventory.ts

@@ -8,6 +8,7 @@ import {
   integer,
   numeric,
   date,
+  pgEnum,
 } from 'drizzle-orm/pg-core'
 import { locations } from './stores.js'
 
@@ -41,6 +42,8 @@ export const suppliers = pgTable('supplier', {
 // See lookups.ts for inventory_unit_status and item_condition tables.
 // Columns below use varchar referencing the lookup slug.
 
+export const taxCategoryEnum = pgEnum('tax_category', ['goods', 'service', 'exempt'])
+
 export const products = pgTable('product', {
   id: uuid('id').primaryKey().defaultRandom(),
   locationId: uuid('location_id').references(() => locations.id),
@@ -54,6 +57,7 @@ export const products = pgTable('product', {
   isSerialized: boolean('is_serialized').notNull().default(false),
   isRental: boolean('is_rental').notNull().default(false),
   isDualUseRepair: boolean('is_dual_use_repair').notNull().default(false),
+  taxCategory: taxCategoryEnum('tax_category').notNull().default('goods'),
   price: numeric('price', { precision: 10, scale: 2 }),
   minPrice: numeric('min_price', { precision: 10, scale: 2 }),
   rentalRateMonthly: numeric('rental_rate_monthly', { precision: 10, scale: 2 }),

packages/backend/src/db/schema/pos.ts

@@ -0,0 +1,165 @@
+import {
+  pgTable,
+  uuid,
+  varchar,
+  text,
+  timestamp,
+  boolean,
+  integer,
+  numeric,
+  pgEnum,
+  jsonb,
+} from 'drizzle-orm/pg-core'
+import { locations } from './stores.js'
+import { accounts } from './accounts.js'
+import { products, inventoryUnits } from './inventory.js'
+import { users } from './users.js'
+import { repairTickets, repairBatches } from './repairs.js'
+
+// --- Enums ---
+
+export const transactionTypeEnum = pgEnum('transaction_type', [
+  'sale',
+  'repair_payment',
+  'rental_deposit',
+  'account_payment',
+  'refund',
+])
+
+export const transactionStatusEnum = pgEnum('transaction_status', [
+  'pending',
+  'completed',
+  'voided',
+  'refunded',
+])
+
+export const paymentMethodEnum = pgEnum('payment_method', [
+  'cash',
+  'card_present',
+  'card_keyed',
+  'check',
+  'account_charge',
+])
+
+export const discountTypeEnum = pgEnum('discount_type', ['percent', 'fixed'])
+
+export const discountAppliesToEnum = pgEnum('discount_applies_to', [
+  'order',
+  'line_item',
+  'category',
+])
+
+export const drawerStatusEnum = pgEnum('drawer_status', ['open', 'closed'])
+
+// --- Tables ---
+
+export const discounts = pgTable('discount', {
+  id: uuid('id').primaryKey().defaultRandom(),
+  locationId: uuid('location_id').references(() => locations.id),
+  name: varchar('name', { length: 255 }).notNull(),
+  discountType: discountTypeEnum('discount_type').notNull(),
+  discountValue: numeric('discount_value', { precision: 10, scale: 2 }).notNull(),
+  appliesTo: discountAppliesToEnum('applies_to').notNull().default('line_item'),
+  requiresApprovalAbove: numeric('requires_approval_above', { precision: 10, scale: 2 }),
+  isActive: boolean('is_active').notNull().default(true),
+  validFrom: timestamp('valid_from', { withTimezone: true }),
+  validUntil: timestamp('valid_until', { withTimezone: true }),
+  createdAt: timestamp('created_at', { withTimezone: true }).notNull().defaultNow(),
+  updatedAt: timestamp('updated_at', { withTimezone: true }).notNull().defaultNow(),
+})
+
+export const drawerSessions = pgTable('drawer_session', {
+  id: uuid('id').primaryKey().defaultRandom(),
+  locationId: uuid('location_id').references(() => locations.id),
+  openedBy: uuid('opened_by')
+    .notNull()
+    .references(() => users.id),
+  closedBy: uuid('closed_by').references(() => users.id),
+  openingBalance: numeric('opening_balance', { precision: 10, scale: 2 }).notNull(),
+  closingBalance: numeric('closing_balance', { precision: 10, scale: 2 }),
+  expectedBalance: numeric('expected_balance', { precision: 10, scale: 2 }),
+  overShort: numeric('over_short', { precision: 10, scale: 2 }),
+  denominations: jsonb('denominations').$type<Record<string, number>>(),
+  status: drawerStatusEnum('status').notNull().default('open'),
+  notes: text('notes'),
+  openedAt: timestamp('opened_at', { withTimezone: true }).notNull().defaultNow(),
+  closedAt: timestamp('closed_at', { withTimezone: true }),
+})
+
+export const transactions = pgTable('transaction', {
+  id: uuid('id').primaryKey().defaultRandom(),
+  locationId: uuid('location_id').references(() => locations.id),
+  transactionNumber: varchar('transaction_number', { length: 50 }).notNull().unique(),
+  accountId: uuid('account_id').references(() => accounts.id),
+  repairTicketId: uuid('repair_ticket_id').references(() => repairTickets.id),
+  repairBatchId: uuid('repair_batch_id').references(() => repairBatches.id),
+  transactionType: transactionTypeEnum('transaction_type').notNull(),
+  status: transactionStatusEnum('status').notNull().default('pending'),
+  subtotal: numeric('subtotal', { precision: 10, scale: 2 }).notNull().default('0'),
+  discountTotal: numeric('discount_total', { precision: 10, scale: 2 }).notNull().default('0'),
+  taxTotal: numeric('tax_total', { precision: 10, scale: 2 }).notNull().default('0'),
+  total: numeric('total', { precision: 10, scale: 2 }).notNull().default('0'),
+  paymentMethod: paymentMethodEnum('payment_method'),
+  amountTendered: numeric('amount_tendered', { precision: 10, scale: 2 }),
+  changeGiven: numeric('change_given', { precision: 10, scale: 2 }),
+  checkNumber: varchar('check_number', { length: 50 }),
+  stripePaymentIntentId: varchar('stripe_payment_intent_id', { length: 255 }),
+  taxExempt: boolean('tax_exempt').notNull().default(false),
+  taxExemptReason: text('tax_exempt_reason'),
+  processedBy: uuid('processed_by')
+    .notNull()
+    .references(() => users.id),
+  drawerSessionId: uuid('drawer_session_id').references(() => drawerSessions.id),
+  notes: text('notes'),
+  completedAt: timestamp('completed_at', { withTimezone: true }),
+  createdAt: timestamp('created_at', { withTimezone: true }).notNull().defaultNow(),
+  updatedAt: timestamp('updated_at', { withTimezone: true }).notNull().defaultNow(),
+})
+
+export const transactionLineItems = pgTable('transaction_line_item', {
+  id: uuid('id').primaryKey().defaultRandom(),
+  transactionId: uuid('transaction_id')
+    .notNull()
+    .references(() => transactions.id),
+  productId: uuid('product_id').references(() => products.id),
+  inventoryUnitId: uuid('inventory_unit_id').references(() => inventoryUnits.id),
+  description: varchar('description', { length: 255 }).notNull(),
+  qty: integer('qty').notNull().default(1),
+  unitPrice: numeric('unit_price', { precision: 10, scale: 2 }).notNull(),
+  discountAmount: numeric('discount_amount', { precision: 10, scale: 2 }).notNull().default('0'),
+  discountReason: text('discount_reason'),
+  taxRate: numeric('tax_rate', { precision: 5, scale: 4 }).notNull().default('0'),
+  taxAmount: numeric('tax_amount', { precision: 10, scale: 2 }).notNull().default('0'),
+  lineTotal: numeric('line_total', { precision: 10, scale: 2 }).notNull().default('0'),
+  createdAt: timestamp('created_at', { withTimezone: true }).notNull().defaultNow(),
+})
+
+export const discountAudits = pgTable('discount_audit', {
+  id: uuid('id').primaryKey().defaultRandom(),
+  transactionId: uuid('transaction_id')
+    .notNull()
+    .references(() => transactions.id),
+  transactionLineItemId: uuid('transaction_line_item_id').references(() => transactionLineItems.id),
+  discountId: uuid('discount_id').references(() => discounts.id),
+  appliedBy: uuid('applied_by')
+    .notNull()
+    .references(() => users.id),
+  approvedBy: uuid('approved_by').references(() => users.id),
+  originalAmount: numeric('original_amount', { precision: 10, scale: 2 }).notNull(),
+  discountedAmount: numeric('discounted_amount', { precision: 10, scale: 2 }).notNull(),
+  reason: text('reason').notNull(),
+  createdAt: timestamp('created_at', { withTimezone: true }).notNull().defaultNow(),
+})
+
+// --- Type exports ---
+
+export type Discount = typeof discounts.$inferSelect
+export type DiscountInsert = typeof discounts.$inferInsert
+export type Transaction = typeof transactions.$inferSelect
+export type TransactionInsert = typeof transactions.$inferInsert
+export type TransactionLineItem = typeof transactionLineItems.$inferSelect
+export type TransactionLineItemInsert = typeof transactionLineItems.$inferInsert
+export type DiscountAudit = typeof discountAudits.$inferSelect
+export type DiscountAuditInsert = typeof discountAudits.$inferInsert
+export type DrawerSession = typeof drawerSessions.$inferSelect
+export type DrawerSessionInsert = typeof drawerSessions.$inferInsert

packages/backend/src/db/schema/stores.ts

@@ -1,4 +1,4 @@
-import { pgTable, uuid, varchar, text, jsonb, timestamp, boolean } from 'drizzle-orm/pg-core'
+import { pgTable, uuid, varchar, text, jsonb, timestamp, boolean, numeric } from 'drizzle-orm/pg-core'
 
 export const companies = pgTable('company', {
   id: uuid('id').primaryKey().defaultRandom(),
@@ -30,6 +30,8 @@ export const locations = pgTable('location', {
   phone: varchar('phone', { length: 50 }),
   email: varchar('email', { length: 255 }),
   timezone: varchar('timezone', { length: 100 }),
+  taxRate: numeric('tax_rate', { precision: 5, scale: 4 }),
+  serviceTaxRate: numeric('service_tax_rate', { precision: 5, scale: 4 }),
   isActive: boolean('is_active').notNull().default(true),
   createdAt: timestamp('created_at', { withTimezone: true }).notNull().defaultNow(),
   updatedAt: timestamp('updated_at', { withTimezone: true }).notNull().defaultNow(),