I've made text editor engine for .NET 10 built in C# with no UI dependencies. Includes a piece-table buffer, multi cursor editing, syntax highlighting, code folding, snippets, TextMate grammars, diff engine, undo/redo, C# REPL, plugin system. Its essentially a deterministic execution runtime for structured, auditable text mutations thats built for AI systems, automation pipelines, and tooling that needs to manipulate text documents. https://github.com/marinusmaurice/TextApi