Why: the 400 (unknown field name) outage shipped because no automated
check drove the UsersPanel create path against the strict backend
contract; this scenario pins the request body, the pending notice, the
table row state and the CLI handoff hint into the composition suite.
Evidence: passing run against the deployed shared dev (SELF, task card).
Impact: e2e/ only; no production code.
Refs: backend 8dfc223, frontend #94