Build OR verify a GiveWell-style BOTEC (back-of-the-envelope cost-effectiveness calculation). Build mode produces a vertical, one-tab-per-program Excel workbook plus a markdown narrative, machine-verifies the arithmetic, and runs a built-in skeptical review loop; headline output is a CE multiple ("Xx benchmark/cash"). Review mode verifies an existing BOTEC's arithmetic, sourcing, counterfactual structure, and plausibility. Use whenever the user wants a BOTEC or quick cost-effectiveness estimate built, OR an existing BOTEC checked, verified, or reviewed.
