Pay at close: document parameters and test with Guardian (Ben)

The team needs clarity on what triggers payment and what counts as "completed enough" for pay-at-close (e.g. report publication in Spectora drove their rules). This needs to be captured and tested with Ben at Guardian so pay-at-close behavior is understood and correct at launch.

Why it matters: Prevents misalignment on when revenue is considered earned and when payment is triggered, avoiding process gaps or disputes.

Note: May be a task/subtask under ATT-176 (Test Real Payments) or a separate implementation doc; confirm in Linear.