What is a brand kit
A brand kit is where a brand stores its colours, its type and its rules once, so nobody has to decide them again on every piece.
A brand kit is not a logo or a PDF manual. It is the short list of decisions a brand already made and does not want to make again: which colours it uses and which one leads, which typeface goes in a headline and which in long text, how much margin a piece breathes, how it signs off, and what tone it speaks in.
The difference from an identity manual is where it lives. A manual gets read, understood, and then applied by eye; a brand kit is a file the pieces read from. When it works, no piece stores a colour: it stores a reference to the kit. Change the colour in the kit and every piece changes, including the ones already made.
Why it matters: nobody recognizes a brand because of one brilliant idea. They recognize it because they saw the same colour, the same type and the same margin thirty times, under thirty different messages. A brand kit is what makes those thirty times come out the same without anyone having to remember anything.
In Piecerun the brand kit is the first thing you load and what rules everything after it: templates inherit from it, and whatever does not match gets flagged before the piece goes out.