go-task/task ? reverse-engineered prompt

Build me a fast, cross platform task runner in Go that works like a modern replacement for Make.

I want a command line tool where I can define tasks in a simple Taskfile and then run them with a short command. It should support things like running shell commands, chaining tasks together, passing variables in, checking if files are up to date, and only rerunning work when needed. Make it handle common dev workflow stuff like setup, build, test, format, watch mode, and shell completion. It should feel easy to use from any project, with helpful output and clear errors.

Please make it work cleanly on Windows, macOS, and Linux, and keep it focused on speed and simplicity. If you need current docs or examples to match expected behavior, look them up online first.