Reduce StartTransaction complexity in TransactionAggregateExtensions

[Copilot]

TransactionAggregateExtensions.StartTransaction exceeded the configured cyclomatic complexity limit due to inline validation and state guard logic. This change keeps behavior intact while separating the method into smaller, purpose-specific helpers.

• What changed

  • Extracted request validation into a dedicated ValidateStartTransactionArguments(...) helper
  • Extracted aggregate state preconditions into CheckCanStartTransaction(...)
  • Left event creation and append flow in StartTransaction(...) so the main path stays linear and easy to follow

• Why this matters

  • Brings StartTransaction under the complexity threshold without changing domain behavior
  • Makes the method read as: validate input → validate state → emit TransactionHasStartedEvent

• Resulting shape

  Result result = ValidateStartTransactionArguments(
      transactionDateTime,
      transactionNumber,
      transactionType,
      transactionReference,
      estateId,
      merchantId,
      deviceIdentifier);
  
  if (result.IsFailed)
      return result;
  
  result = CheckCanStartTransaction(aggregate);
  if (result.IsFailed)
      return result;

• Behavior preserved

  • Existing validation rules for transaction date/time, number, reference, type, estate, merchant, and device identifier remain unchanged
  • Existing guards preventing a transaction from being started twice or after completion remain unchanged
  • Event payload and append behavior are unchanged

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• f.feedz.io
  • Triggering command: /usr/bin/dotnet dotnet test /home/REDACTED/work/TransactionProcessor/TransactionProcessor/TransactionProcessor.Tests/TransactionProcessor.Tests.csproj --filter VerifyBootstrapperIsValid --no-restore -nologo (dns block)
  • Triggering command: /usr/bin/dotnet dotnet test /home/REDACTED/work/TransactionProcessor/TransactionProcessor/TransactionProcessor.Aggregates.Tests/TransactionProcessor.Aggregates.Tests.csproj --filter TransactionAggregate_StartTransaction -p:RestoreIgnoreFailedSources=true -nologo (dns block)
  • Triggering command: /usr/bin/dotnet dotnet restore /home/REDACTED/work/TransactionProcessor/TransactionProcessor/TransactionProcessor.Aggregates.Tests/TransactionProcessor.Aggregates.Tests.csproj -p:RestoreIgnoreFailedSources=true -nologo (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
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Original prompt

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This section details on the original issue you should resolve

<issue_title>[Complexity] Method TransactionAggregateExtensions::StartTransaction has a cyclomatic complexity of 11 (limit is 8)</issue_title>
<issue_description>Codacy ID: f0db1afda6b8079e9c3b8b89a6d68765

File: TransactionProcessor.Aggregates/TransactionAggregate.cs
Line: 495
Rule: Complexity (Warning)
Commit: d86ddd7f1bcabe1f21d4be000e4eda81d82ca1d5

Message: Method TransactionAggregateExtensions::StartTransaction has a cyclomatic complexity of 11 (limit is 8)

**Code Snippet:**
```csharp
        public static Result StartTransaction(this TransactionAggregate aggregate, 
```

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [Complexity] Method TransactionAggregateExtensions::StartTransaction has a cyclomatic complexity of 11 (limit is 8) #1408

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