good point, single type source is very appealing and LLMs are so good with TS because of those type interfaces.

only downside is forced js ecosystem x_X

Agree, as for the JS/TS lock-in, we could have applied a similar approach with other languages too, but we intentionally chose to focus on one single stack to create a seamless end-to-end experience instead of providing a generic solution for multiple stacks, because a lot of the problems we're solving are different based on what stack you choose.