cost_guardrail

A wrong unit cost on a PO receipt quietly rewrites the product's standard price, and every later sale books nonsense COGS. Nobody notices until the month-end margin report looks insane and somebody spends two days working out why.

• ✓ Per-category percentage threshold blocks an abnormal receipt cost before it lands
• ✓ Per-category maximum multiple clamps runaway COGS on invoices, with an alert
• ✓ Optionally block credit notes that reverse COGS with no goods return
• ✓ Scoped COGS cleanup wizard — preview, then post through a clearing account
• ✓ All guards off by default; installing changes nothing
• ✓ Ships with its own test suite — 8 tests, all passing