Agents keep raising our db pool max, and the only fix that's held is a test

src/db/pool.ts sets max to 4. That's not a tuning choice, it's the plan we're on, and a couple of background jobs draw on the same ceiling. Nothing in the file said any of that. Every agent I've pointed at that repo has raised the number sooner or later, and it hasn't been one tool doing it. Usually just a bigger constant, once os.cpus().length * 4 with a comment about throughput. It reads fine in the diff, because on its own it is fine. The part that isn't fine turns up later, when the nightly job can't get a connection and someone loses a morning working out why. A line in AGENTS.md about leaving the pool size alone gets respected maybe half the time. A comment sitting directly above the value did better than that, which I still can't explain. What's held is a test that fails if max goes over 4. Three lines, and it's the only test in that file. Over the past month verdent has gotten better at guessing how I'd name a test, which isn't the kind of thing that helps with this. Same repo, scripts/seed.ts has been broken since February and nobody noticed, since everyone restores from a dump anyway. The 4 isn't a fact about the code, it's a fact about the invoice, and a test is the only place I've found to put one where an agent runs into it. If you keep constraints like that somewhere else, I'd take the pointer.