Modern C# and .NET Upgrade

Select a supported .NET target framework using the LTS/STS support policy and a project's deployment constraints.

Configure solution-wide compiler settings, nullable analysis, and code-quality analyzers with Directory.Build.props.

Eliminate nullability warnings in an existing C# code path without suppressing valid diagnostics.

Model immutable API contracts and value objects using records, init-only properties, and required members.

Refactor complex conditional logic using modern C# pattern matching.

Implement an asynchronous I/O workflow that propagates CancellationToken correctly.