“If this friendship had a private charter — the two or three things we quietly promise each other by just being who we are — what would they actually be?”

A set-piece. One table, two pens, the same evening, one joint artefact. These are the pages people photograph.

Why this question

The unspoken rules that have kept us intact. Which do we still need, and which might we loosen or add?

And once you’ve both answered

Draft your clauses separately, then agree the final charter together in the middle of the page — and sign it.

Answering it honestly

One table, two pens, the same evening. This one doesn't work by correspondence.
Argue about the details out loud before anything gets written down. The arguing is part of the artefact.
Finish in the sitting. A half-built set-piece has a way of staying half-built.

And the house rule, whatever the mode: leave a blank rather than write a lie. A blank can be filled later; a lie sits in the archive forever, and you both have to live with the paperwork.