Make C# ambient-dependent behavior testable and add deterministic tests. USE FOR: DateTime/Task.Delay/File/Environment/Guid/Random, constructor injection for instance classes, preserving static APIs, nested override restore, parallel isolation, or no real I/O. DO NOT USE FOR: audits, wrapper-only/bu
Make C# ambient-dependent behavior testable and add deterministic tests. USE FOR: DateTime/Task.Delay/File/Environment/Guid/Random, constructor injection for instance classes, preserving static APIs, nested override restore, parallel isolation, or no real I/O. DO NOT USE FOR: audits, wrapper-only/bulk migration, or an existing injectable seam.