rpsft/etlbox — reverse-engineered prompt

Build me a lightweight open source ETL toolkit for .NET in C#. I want something people can add to a normal .NET project to move data from databases, files, and a few common web or messaging systems, transform rows in memory, and load the results somewhere else. It should feel easy to wire together a source, optional transforms like filtering, mapping, validation, cleaning, aggregation, and branching, then send data to one or more destinations.

Please also include simple control flow helpers for common database tasks and running SQL, plus solid logging so job runs are easy to monitor and troubleshoot. It should run on Windows, macOS, and Linux, work well with current .NET, and be usable for both small jobs and larger parallel data flows. Add clear docs and a few tutorial style examples, especially one that reads from a database, changes values, and writes to both another table and a CSV file. Good test coverage would be great too. Look up current docs online if you need to.