A clef change does not by itself require (or forbid) restating the key signature

A clef change and a key-signature change are independent events — changing clef alone never requires the key signature to be restated at that point (since the key signature already repeats at the start of every SYSTEM regardless, per clef-repeated-every-system, a mid-system clef change with no accompanying key change simply carries on with the same key, unrestated, since it was never in question). The key signature IS restated at a mid-system clef change only if the key is ALSO changing at that same point, in which case both the new clef and the new key signature are engraved together, new-clef-then-new-key, at that point in the score.

A mid-passage clef change (once authorable) that superfluously restates an unchanged key signature at that point, cluttering the score with a redundant accidental-count reminder the reader does not need mid-system.

Gould, Behind Bars, Key Signatures chapter and Clefs chapter both confirm these are independent, orthogonal events. Ross, The Art of Music Engraving, agrees.

This rule can be decided from pitches, durations and voices — no layout required. A validator can check it before anything is drawn.