Adding a rule to an…
Agent system prompts rot the same way every time: each fix tacks on a sentence, nothing ever comes off, and the prompt grows forever. Two things break as a result — the prompt drifts past whatever size budget you have, and (the subtle one) the prompt's prose is the agent's prose. A verbose, redundant constitution teaches a verbose, redundant writing voice. So make every addition carry a matching subtraction. When you add a rule, find the existing rule it makes redundant and cut it. In practice the new rule almost always overlaps something — a preamble about "only ask when a decision genuinely needs the human" makes a stale "no confirmation requests for obvious next steps" bullet redundant; fold one into the other. The part people skip: don't eyeball whether the wording "fits" — measure it. Render the prompt with all includes expanded, byte-count it, and compare against a budget: # render each role's full prompt and check it against a per-role ceiling for…