The estimate is a document you can argue with
Effort is stated in person-days against a named work breakdown, not a range with contingency hidden inside it. The custody platform resolved to 1,256 person-days across 26 weeks, published line by line, because a number a procurement committee can audit is the only kind that survives one. The architecture decision record — every integration point, data flow and security boundary — is settled before production code begins, and change control is written down. That is why the estimate tends to hold.
