feat: add cash rounding, POS test suite, and fix test harness port cleanup

- Add Swedish rounding (nearest nickel) for cash payments at locations with cash_rounding enabled
- Add rounding_adjustment column to transactions, cash_rounding to locations
- Add POS schema to database plugin for relational query support
- Complete/void routes now return full transaction with line items via getById
- Test harness killPort falls back to fuser when lsof unavailable (fixes stale process bug)
- Add 35-test POS API suite covering discounts, drawer, transactions, tax, rounding, e2e flow
- Add unit tests for tax service and POS Zod schemas

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

packages/backend/src/db/migrations/0038_pos-core.sql

@@ -0,0 +1,111 @@
+-- POS core: enums, tables, and new columns on existing tables
+
+-- New enums
+CREATE TYPE "public"."transaction_type" AS ENUM('sale', 'repair_payment', 'rental_deposit', 'account_payment', 'refund');
+CREATE TYPE "public"."transaction_status" AS ENUM('pending', 'completed', 'voided', 'refunded');
+CREATE TYPE "public"."payment_method" AS ENUM('cash', 'card_present', 'card_keyed', 'check', 'account_charge');
+CREATE TYPE "public"."discount_type" AS ENUM('percent', 'fixed');
+CREATE TYPE "public"."discount_applies_to" AS ENUM('order', 'line_item', 'category');
+CREATE TYPE "public"."drawer_status" AS ENUM('open', 'closed');
+CREATE TYPE "public"."tax_category" AS ENUM('goods', 'service', 'exempt');
+
+-- New columns on existing tables
+ALTER TABLE "product" ADD COLUMN "tax_category" "tax_category" NOT NULL DEFAULT 'goods';
+ALTER TABLE "location" ADD COLUMN "tax_rate" numeric(5, 4) NOT NULL DEFAULT '0';
+ALTER TABLE "location" ADD COLUMN "service_tax_rate" numeric(5, 4) NOT NULL DEFAULT '0';
+
+-- Discount table
+CREATE TABLE "discount" (
+  "id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
+  "location_id" uuid REFERENCES "location"("id"),
+  "name" varchar(255) NOT NULL,
+  "discount_type" "discount_type" NOT NULL,
+  "discount_value" numeric(10, 2) NOT NULL,
+  "applies_to" "discount_applies_to" NOT NULL DEFAULT 'line_item',
+  "requires_approval_above" numeric(10, 2),
+  "is_active" boolean NOT NULL DEFAULT true,
+  "valid_from" timestamp with time zone,
+  "valid_until" timestamp with time zone,
+  "created_at" timestamp with time zone NOT NULL DEFAULT now(),
+  "updated_at" timestamp with time zone NOT NULL DEFAULT now()
+);
+
+-- Drawer session table
+CREATE TABLE "drawer_session" (
+  "id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
+  "location_id" uuid REFERENCES "location"("id"),
+  "opened_by" uuid NOT NULL REFERENCES "user"("id"),
+  "closed_by" uuid REFERENCES "user"("id"),
+  "opening_balance" numeric(10, 2) NOT NULL,
+  "closing_balance" numeric(10, 2),
+  "expected_balance" numeric(10, 2),
+  "over_short" numeric(10, 2),
+  "denominations" jsonb,
+  "status" "drawer_status" NOT NULL DEFAULT 'open',
+  "notes" text,
+  "opened_at" timestamp with time zone NOT NULL DEFAULT now(),
+  "closed_at" timestamp with time zone
+);
+
+-- Transaction table
+CREATE TABLE "transaction" (
+  "id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
+  "location_id" uuid REFERENCES "location"("id"),
+  "transaction_number" varchar(50) NOT NULL UNIQUE,
+  "account_id" uuid REFERENCES "account"("id"),
+  "repair_ticket_id" uuid REFERENCES "repair_ticket"("id"),
+  "repair_batch_id" uuid REFERENCES "repair_batch"("id"),
+  "transaction_type" "transaction_type" NOT NULL,
+  "status" "transaction_status" NOT NULL DEFAULT 'pending',
+  "subtotal" numeric(10, 2) NOT NULL DEFAULT '0',
+  "discount_total" numeric(10, 2) NOT NULL DEFAULT '0',
+  "tax_total" numeric(10, 2) NOT NULL DEFAULT '0',
+  "total" numeric(10, 2) NOT NULL DEFAULT '0',
+  "payment_method" "payment_method",
+  "amount_tendered" numeric(10, 2),
+  "change_given" numeric(10, 2),
+  "check_number" varchar(50),
+  "stripe_payment_intent_id" varchar(255),
+  "tax_exempt" boolean NOT NULL DEFAULT false,
+  "tax_exempt_reason" text,
+  "processed_by" uuid NOT NULL REFERENCES "user"("id"),
+  "drawer_session_id" uuid REFERENCES "drawer_session"("id"),
+  "notes" text,
+  "completed_at" timestamp with time zone,
+  "created_at" timestamp with time zone NOT NULL DEFAULT now(),
+  "updated_at" timestamp with time zone NOT NULL DEFAULT now()
+);
+
+-- Transaction line item table
+CREATE TABLE "transaction_line_item" (
+  "id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
+  "transaction_id" uuid NOT NULL REFERENCES "transaction"("id"),
+  "product_id" uuid REFERENCES "product"("id"),
+  "inventory_unit_id" uuid REFERENCES "inventory_unit"("id"),
+  "description" varchar(255) NOT NULL,
+  "qty" integer NOT NULL DEFAULT 1,
+  "unit_price" numeric(10, 2) NOT NULL,
+  "discount_amount" numeric(10, 2) NOT NULL DEFAULT '0',
+  "discount_reason" text,
+  "tax_rate" numeric(5, 4) NOT NULL DEFAULT '0',
+  "tax_amount" numeric(10, 2) NOT NULL DEFAULT '0',
+  "line_total" numeric(10, 2) NOT NULL DEFAULT '0',
+  "created_at" timestamp with time zone NOT NULL DEFAULT now()
+);
+
+-- Discount audit table (append-only)
+CREATE TABLE "discount_audit" (
+  "id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
+  "transaction_id" uuid NOT NULL REFERENCES "transaction"("id"),
+  "transaction_line_item_id" uuid REFERENCES "transaction_line_item"("id"),
+  "discount_id" uuid REFERENCES "discount"("id"),
+  "applied_by" uuid NOT NULL REFERENCES "user"("id"),
+  "approved_by" uuid REFERENCES "user"("id"),
+  "original_amount" numeric(10, 2) NOT NULL,
+  "discounted_amount" numeric(10, 2) NOT NULL,
+  "reason" text NOT NULL,
+  "created_at" timestamp with time zone NOT NULL DEFAULT now()
+);
+
+-- SKU unique partial index (from prior untracked migration)
+CREATE UNIQUE INDEX IF NOT EXISTS products_sku_unique ON product (sku) WHERE sku IS NOT NULL;

packages/backend/src/db/migrations/0038_product_sku_unique.sql

@@ -1,2 +0,0 @@
--- Add unique index on products.sku (null values are excluded from uniqueness)
-CREATE UNIQUE INDEX IF NOT EXISTS products_sku_unique ON product (sku) WHERE sku IS NOT NULL;

packages/backend/src/db/migrations/0039_cash-rounding.sql

@@ -0,0 +1,3 @@
+-- Cash rounding: location setting + transaction adjustment tracking
+ALTER TABLE "location" ADD COLUMN "cash_rounding" boolean NOT NULL DEFAULT false;
+ALTER TABLE "transaction" ADD COLUMN "rounding_adjustment" numeric(10, 2) NOT NULL DEFAULT '0';

packages/backend/src/db/migrations/meta/_journal.json

@@ -267,6 +267,20 @@
       "when": 1774970000000,
       "tag": "0037_rate_cycles",
       "breakpoints": true
+    },
+    {
+      "idx": 38,
+      "version": "7",
+      "when": 1775321562910,
+      "tag": "0038_pos-core",
+      "breakpoints": true
+    },
+    {
+      "idx": 39,
+      "version": "7",
+      "when": 1775408000000,
+      "tag": "0039_cash-rounding",
+      "breakpoints": true
     }
   ]
 }

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

@@ -104,6 +104,7 @@ export const transactions = pgTable('transaction', {
   changeGiven: numeric('change_given', { precision: 10, scale: 2 }),
   checkNumber: varchar('check_number', { length: 50 }),
   stripePaymentIntentId: varchar('stripe_payment_intent_id', { length: 255 }),
+  roundingAdjustment: numeric('rounding_adjustment', { precision: 10, scale: 2 }).notNull().default('0'),
   taxExempt: boolean('tax_exempt').notNull().default(false),
   taxExemptReason: text('tax_exempt_reason'),
   processedBy: uuid('processed_by')

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

@@ -32,6 +32,7 @@ export const locations = pgTable('location', {
   timezone: varchar('timezone', { length: 100 }),
   taxRate: numeric('tax_rate', { precision: 5, scale: 4 }),
   serviceTaxRate: numeric('service_tax_rate', { precision: 5, scale: 4 }),
+  cashRounding: boolean('cash_rounding').notNull().default(false),
   isActive: boolean('is_active').notNull().default(true),
   createdAt: timestamp('created_at', { withTimezone: true }).notNull().defaultNow(),
   updatedAt: timestamp('updated_at', { withTimezone: true }).notNull().defaultNow(),

packages/backend/src/plugins/database.ts

@@ -5,8 +5,9 @@ import * as storeSchema from '../db/schema/stores.js'
 import * as userSchema from '../db/schema/users.js'
 import * as accountSchema from '../db/schema/accounts.js'
 import * as inventorySchema from '../db/schema/inventory.js'
+import * as posSchema from '../db/schema/pos.js'
 
-const schema = { ...storeSchema, ...userSchema, ...accountSchema, ...inventorySchema }
+const schema = { ...storeSchema, ...userSchema, ...accountSchema, ...inventorySchema, ...posSchema }
 
 declare module 'fastify' {
   interface FastifyInstance {

packages/backend/src/routes/v1/transactions.ts

@@ -78,13 +78,15 @@ export const transactionRoutes: FastifyPluginAsync = async (app) => {
     if (!parsed.success) {
       return reply.status(400).send({ error: { message: 'Validation failed', details: parsed.error.flatten(), statusCode: 400 } })
     }
-    const txn = await TransactionService.complete(app.db, id, parsed.data)
+    await TransactionService.complete(app.db, id, parsed.data)
+    const txn = await TransactionService.getById(app.db, id)
     return reply.send(txn)
   })
 
   app.post('/transactions/:id/void', { preHandler: [app.authenticate, app.requirePermission('pos.admin')] }, async (request, reply) => {
     const { id } = request.params as { id: string }
-    const txn = await TransactionService.void(app.db, id, request.user.id)
+    await TransactionService.void(app.db, id, request.user.id)
+    const txn = await TransactionService.getById(app.db, id)
     return reply.send(txn)
   })
 }

packages/backend/src/services/drawer.service.ts

@@ -32,8 +32,12 @@ export const DrawerService = {
     if (session.status === 'closed') throw new ConflictError('Drawer session is already closed')
 
     // Calculate expected balance from cash transactions in this drawer session
-    const [cashTotal] = await db
-      .select({ total: sum(transactions.total) })
+    // Net cash kept = total + rounding_adjustment (change is already accounted for)
+    const [cashTotals] = await db
+      .select({
+        total: sum(transactions.total),
+        rounding: sum(transactions.roundingAdjustment),
+      })
       .from(transactions)
       .where(
         and(
@@ -43,7 +47,7 @@ export const DrawerService = {
         )
       )
 
-    const cashIn = parseFloat(cashTotal?.total ?? '0')
+    const cashIn = parseFloat(cashTotals?.total ?? '0') + parseFloat(cashTotals?.rounding ?? '0')
     const openingBalance = parseFloat(session.openingBalance)
     const expectedBalance = openingBalance + cashIn
     const closingBalance = input.closingBalance

packages/backend/src/services/tax.service.ts

@@ -44,6 +44,14 @@ export const TaxService = {
     return Math.round(amount * rate * 100) / 100
   },
 
+  /**
+   * Swedish rounding: round to nearest $0.05 for cash payments.
+   * Only affects the final total — tax and line items stay exact.
+   */
+  roundToNickel(amount: number): number {
+    return Math.round(amount * 20) / 20
+  },
+
   /**
    * Map repair line item types to tax categories:
    * - "part"      → goods (taxable)

packages/backend/src/services/transaction.service.ts

@@ -231,10 +231,26 @@ export const TransactionService = {
     if (!txn) throw new NotFoundError('Transaction')
     if (txn.status !== 'pending') throw new ConflictError('Transaction is not pending')
 
-    // Validate cash payment
+    // Validate cash payment (with optional nickel rounding)
     let changeGiven: string | undefined
+    let roundingAdjustment = 0
     if (input.paymentMethod === 'cash') {
-      const total = parseFloat(txn.total)
+      let total = parseFloat(txn.total)
+
+      // Apply Swedish rounding if location has cash_rounding enabled
+      if (txn.locationId) {
+        const [loc] = await db
+          .select({ cashRounding: locations.cashRounding })
+          .from(locations)
+          .where(eq(locations.id, txn.locationId))
+          .limit(1)
+        if (loc?.cashRounding) {
+          const rounded = TaxService.roundToNickel(total)
+          roundingAdjustment = Math.round((rounded - total) * 100) / 100
+          total = rounded
+        }
+      }
+
       if (!input.amountTendered || input.amountTendered < total) {
         throw new ValidationError('Amount tendered must be >= transaction total for cash payments')
       }
@@ -273,13 +289,13 @@ export const TransactionService = {
         paymentMethod: input.paymentMethod,
         amountTendered: input.amountTendered?.toString(),
         changeGiven,
+        roundingAdjustment: roundingAdjustment.toString(),
         checkNumber: input.checkNumber,
         completedAt: new Date(),
         updatedAt: new Date(),
       })
       .where(eq(transactions.id, transactionId))
       .returning()
-
     return completed
   },