alt Hacker NewsI am the author of hax, yes.
If you are familiar with pi, then some of the key features listed on the GitHub page (and website) already illustrate substantial differences: hax is much smaller in footprint (I wouldn't even call pi "light-weight", really - heavy js runtime with a lot of dependencies), hax preserves native terminal scrollback (pi uses alt-screen fullscreen, or clears in some cases in differential mode), hax uses normal XDG dirs (pi uses ~/.pi), hax is extended out-of-process (pi suggests in-process plugins).
There are other differences in presentation, and in features (for example, hax has background bash invocation out-of-the-box). Not practical to list all of them.
Thanks I'll have to set aside some time later to try it out. It's kind of a sliding scale, but pi is definitely lighter-weight when compared to harnesses like Opencode and the all-batteries included "Oh-My-Pi".
And of course, “lightweight” does have a lot of interpretations where harnesses are concerned (memory footprint, binary size, performance, system prompt, etc).