A requirement the spck.dev suite checks on UCP servers. The quoted text is the normative requirement; the citation links to the exact line of the pinned spec source it was taken from.
Each PUT replaces the entire session, so clients must include all previously set fields they wish to retain
A deviation on a MUST fails the run and shows the requirement next to the actual response. Checks the suite cannot validate soundly are reported inconclusive or not-tested — never a silent pass. The full verdict semantics are on the grading rubric.
The hosted check covers the read-only surface; the CLI and GitHub Action run the full suite, including this check when your store declares the capability it belongs to.