Performance you do not have to remember

Every decision below started as a measurement, not a preference. The theme ships the result, and the reasoning stays attached to it so the next person can disagree on the evidence.

What the system actually guarantees

Three things, and only three. Everything else is a convention you can change without breaking anything.

• One page-level grid, so cross-block alignment is structural.
• One rhythm value, declared once.
• One place a token is defined, and one place it is consumed.

A generated token nobody reads is the system silently not working.

If any of that stops being true, the tests fail before the page does.