Does that tool already exist, so do you have a specific TS subset in mind you are aiming for? Or you are simply trying to use fewer complex features?

No the tool does not exist. Its medium to long term vision.

Our backends are structured on isolated units - what we call "features". Features invoke another features via fully qualified names using a standard Features.send(...). in-process/inter-replica/inter-service and even seperate functions inside the same js files are all invoked likewise.

Only a few specific helper functions for a feature exist for direct invocations.

The complexity of ts2rust tool is thus greatly reduced because of the discipline of the architecture.