Over the last few days, I sepent time refining architectural patterns in a modular .NET backend centered around payroll processing, approvals, and workflow-driven operations. One area I focused on heavily was aggregate design and state protection. Instead of exposing mutable collections directly from entities, aggregates internally manage their own state exposing read-only access externally. private readonly List _monthlyAllowance = new(); public IReadOnlyCollection MonthlyAllowances => _monthlyAllowance ; This prevents external code from bypassing aggregate rules; employee.MonthlyAllowances.Add(...) while still allowing controlled state transitions through aggregate methods: public void AddMonthlyAllowance(MonthlyAllowance allowance) { if(_monthlyAllowances.Any(x => x.PayrollMonth == allowance.PayrollMonth && x.SalaryItemId == allowance.SalaryItemId)) { throw new DuplicateMonthlyAllowanceException(); } _monthlyAllowances.Add(allowance); } Another major refinement was moving workflow reactions…