Capstone Reference Implementation: Data Layer and Apex

public inherited sharing class CaseSelector {
    public static List<Case> openCases() {
        return Database.query(
            'SELECT Id, Subject, Status, AccountId FROM Case WHERE IsClosed = false ORDER BY CreatedDate DESC',
            AccessLevel.USER_MODE
        );
    }
}

public inherited sharing class AccountSelector {
    public static Account summaryById(Id accountId) {
        List<Account> results = Database.query(
            'SELECT Id, Name, Industry, (SELECT Id, Amount FROM Opportunities WHERE IsClosed = false) ' +
            'FROM Account WHERE Id = :accountId',
            AccessLevel.USER_MODE
        );
        return results.isEmpty() ? null : results[0];
    }
}

Each Selector owns exactly one query concern, isolated so it can change independently of the business logic that consumes it (Module 16).

public inherited sharing class CommandCenterService {
    public static List<CaseSummary> getOpenCases() {
        List<CaseSummary> summaries = new List<CaseSummary>();
        for (Case c : CaseSelector.openCases()) {
            summaries.add(new CaseSummary(c.Id, c.Subject, c.Status, c.AccountId));
        }
        return summaries;
    }

    public static AccountSummary getAccountSummary(Id accountId) {
        Account acc = AccountSelector.summaryById(accountId);
        if (acc == null) {
            throw new AuraHandledException('Account not found.');
        }

        Decimal openPipeline = 0;
        for (Opportunity opp : acc.Opportunities) {
            openPipeline += opp.Amount;
        }
        return new AccountSummary(acc.Id, acc.Name, acc.Industry, openPipeline);
    }

    public static void updateCaseStatus(Id caseId, String newStatus) {
        if (String.isBlank(newStatus)) {
            throw new AuraHandledException('A status is required.');
        }
        Database.update(new Case(Id = caseId, Status = newStatus), AccessLevel.USER_MODE);
    }
}

No @AuraEnabled annotations here at all (Module 16) — this class doesn't know or care that LWC exists, keeping it independently testable and reusable. AuraHandledException (Module 7) surfaces safe, specific validation messages.

public with sharing class CommandCenterController {
    @AuraEnabled(cacheable=true)
    public static List<CaseSummary> getOpenCases() {
        return CommandCenterService.getOpenCases();
    }

    @AuraEnabled(cacheable=true)
    public static AccountSummary getAccountSummary(Id accountId) {
        return CommandCenterService.getAccountSummary(accountId);
    }

    @AuraEnabled
    public static void updateCaseStatus(Id caseId, String newStatus) {
        CommandCenterService.updateCaseStatus(caseId, newStatus);
    }
}

Every method here is a one-line pass-through — genuinely thin, exactly as planned in Lesson 1. getOpenCases/getAccountSummary are cacheable=true for @wire (read-only); updateCaseStatus isn't, since it performs DML and is called imperatively (Module 7).