Write the architecture down before you write the code
A page of prose costs an afternoon and settles the arguments that would otherwise be settled in a pull request three weeks later.
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The argument against writing the design down is always speed. It is a bad argument, because the alternative is not "start sooner"; it is "discover the disagreement later, in code, when reversing it is expensive".
What the document is for
Not the diagram. The diagram is the easy half and the half that gets shown. The useful part is the paragraph under it explaining which parts genuinely need a model and which parts are better off deterministic, because that is the decision the whole system is downstream of.
What it is not for
It is not a specification to be followed to the letter, and treating it as one produces the padding that a technical reader notices immediately. It is a record of what was decided and why, so the next person, who is often you, can tell the difference between a considered choice and an accident.
This post is a placeholder shipped with the writing section. Replace the body with the real piece; the frontmatter above is the only thing the site reads.