Our calculator pages stop a visitor from typing a negative rent or a negative visitor count. The engines behind them (calc.mjs) often don't, and since the MCP tools in platform/agents/tools.mjs call those engines directly, an agent can hand them any number.
platform/ci/calc_negatives.mjs sets each numeric default to -1 and flags the field when the engine neither refuses it (throws, returns warnings or a null result) nor behaves exactly as it does for 0. Run over all 990 calc.mjs files: 21 calculators, 106 fields. Some are legitimate (capital losses, signed balances), so it is a report, not a gate.
Fixed in this change: u-pick-farm-profit-planner and shared-kitchen-rate-planner (negatives now count as 0, matching their pages), and sbir-budget-builder and mosquito-control-program-pricing-calculator (they now return a warning naming the field). A -1 rent used to raise profit by $1 per season; small, but silent.
The rest of the list is the next run's queue: run the fleet one-liner in the tool's header.