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
     }
   ]
 }