Array.isArray refinement loses the array's type

I realize there are a number of related issues. However, some where about ReadonlyArray, some didn't see directly related at all even though it was pointed there.

Also, this is a much smaller example, just a single line of code really:

Playground link

I know people will point to this ir that implementation or design decision detail — honestly guys, you got it REVERSED. The tool should serve the purpose, not the other way around!

That the array loses all it's type information in such a simple example is A BUG.

And it is possible to do much better: See here! I'm only pointing this out because at times the responses sound like "We tried everything but it is just not possible" when the competition shows that it is actually quite possible.

Related(?): #17002

Beginne damit, das einzeilige Beispiel im verlinkten TypeScript Playground nachzustellen, und vergleiche den abgeleiteten Typ vor und nach der Verfeinerung durch Array.isArray. Lies den zugehörigen Issue #17002 und die bestehende Diskussion als Kontext. Als abgeschlossen gilt die Aufgabe, wenn die Verfeinerung in diesem Beispiel und in relevanten Fällen die Typinformationen des Arrays bewahrt.