feat: add drawer cash in/out adjustments with balance reconciliation

- New drawer_adjustment table (type: cash_in/cash_out, amount, reason)
- POST/GET /drawer/:id/adjustments endpoints
- Drawer close calculation now includes adjustments: expected = opening + sales + cash_in - cash_out
- DrawerAdjustmentSchema for input validation
- 5 new tests (44 total POS tests passing)

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

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

@@ -1,8 +1,8 @@
-import { eq, and, count, sum, type Column } from 'drizzle-orm'
+import { eq, and, count, sum, sql, type Column } from 'drizzle-orm'
 import type { PostgresJsDatabase } from 'drizzle-orm/postgres-js'
-import { drawerSessions, transactions } from '../db/schema/pos.js'
+import { drawerSessions, drawerAdjustments, transactions } from '../db/schema/pos.js'
 import { ConflictError, NotFoundError } from '../lib/errors.js'
-import type { DrawerOpenInput, DrawerCloseInput, PaginationInput } from '@lunarfront/shared/schemas'
+import type { DrawerOpenInput, DrawerCloseInput, DrawerAdjustmentInput, PaginationInput } from '@lunarfront/shared/schemas'
 import { withPagination, withSort, paginatedResponse } from '../utils/pagination.js'
 
 export const DrawerService = {
@@ -47,9 +47,20 @@ export const DrawerService = {
         )
       )
 
-    const cashIn = parseFloat(cashTotals?.total ?? '0') + parseFloat(cashTotals?.rounding ?? '0')
+    // Calculate net drawer adjustments (cash_in adds, cash_out subtracts)
+    const [adjTotals] = await db
+      .select({
+        cashIn: sql<string>`coalesce(sum(case when ${drawerAdjustments.type} = 'cash_in' then ${drawerAdjustments.amount} else 0 end), 0)`,
+        cashOut: sql<string>`coalesce(sum(case when ${drawerAdjustments.type} = 'cash_out' then ${drawerAdjustments.amount} else 0 end), 0)`,
+      })
+      .from(drawerAdjustments)
+      .where(eq(drawerAdjustments.drawerSessionId, sessionId))
+
+    const salesCashIn = parseFloat(cashTotals?.total ?? '0') + parseFloat(cashTotals?.rounding ?? '0')
+    const adjCashIn = parseFloat(adjTotals?.cashIn ?? '0')
+    const adjCashOut = parseFloat(adjTotals?.cashOut ?? '0')
     const openingBalance = parseFloat(session.openingBalance)
-    const expectedBalance = openingBalance + cashIn
+    const expectedBalance = openingBalance + salesCashIn + adjCashIn - adjCashOut
     const closingBalance = input.closingBalance
     const overShort = closingBalance - expectedBalance
 
@@ -93,6 +104,31 @@ export const DrawerService = {
     return session ?? null
   },
 
+  async addAdjustment(db: PostgresJsDatabase<any>, sessionId: string, input: DrawerAdjustmentInput, createdBy: string, approvedBy?: string) {
+    const session = await this.getById(db, sessionId)
+    if (!session) throw new NotFoundError('Drawer session')
+    if (session.status === 'closed') throw new ConflictError('Cannot adjust a closed drawer')
+
+    const [adjustment] = await db
+      .insert(drawerAdjustments)
+      .values({
+        drawerSessionId: sessionId,
+        type: input.type,
+        amount: input.amount.toString(),
+        reason: input.reason,
+        createdBy,
+      })
+      .returning()
+    return adjustment
+  },
+
+  async getAdjustments(db: PostgresJsDatabase<any>, sessionId: string) {
+    return db
+      .select()
+      .from(drawerAdjustments)
+      .where(eq(drawerAdjustments.drawerSessionId, sessionId))
+  },
+
   async list(db: PostgresJsDatabase<any>, params: PaginationInput) {
     const sortableColumns: Record<string, Column> = {
       opened_at: drawerSessions.openedAt,