Looks terrific! I have a suggestion as you continue to add features and think about scripting. sc-im has lua external functions, but you cannot pass a range of cells, only the value of one cell. This severely limits the usefulness of external lua scripts. If/when you add scripting, hopefully you can overcome this limitation. If so, you'll have at least one more user!
I see the value, but I'm not sure if I'd be confident enough to add proper scripting yet, as this requires a lot of attention towards a stable API.
Nonetheless, I think it's an intersting discussion to put on the roadmap: https://github.com/garritfra/cell/issues/23 (RFC sketched out by AI)
Thanks!
https://github.com/andmarti1424/sc-im
Saved you all a search: It seems like it is similar software written in C