A key signature change requires explicit cancellation naturals for every accidental removed from the old signature not present in the new one

Any sharp/flat in the OLD signature absent from the NEW one must be cancelled with an explicit natural before the new signature, in standard cancellation order (reverse of the order the accidentals were originally added, following the circle of fifths).

A modulation from D major (F#, C#) to C major omits the sharps with no cancellation naturals shown.

Gould, 'Key signatures' chapter, explicit diagram; Read ch.5; universal convention implemented by Dorico/Finale/Sibelius/LilyPond.

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