There is no dedicated triple script runtime at this time, although treason is the codename given to the hypothetical reference runtime that we eventually plan to implement. It will likely be based on a fork of Fabrice Bellard's QuickJS and start out as being command-line only (and live that way for some time).
Because of the general properties of triple scripts, however, a treason-like runtime (i.e. one specifically built to run triple scripts, unlike the browser which incidentally runs triple scripts) itself implemented as a triple script, is both possible and tractable. This will be essential for prototyping and provide a good platform to develop an officially blessed runtime for legacy systems (i.e., a way to approximate "running treason in the browser"). The same starting point would be a good candidate for developing the VSCode integration (in the form of an official extension from triplescripts.org).