secrets: maps a requirement to several files under local names. Each local name is
its own need, its own pair credential (the pair is keyed on it: migration 0027),
its own file on the consumer, its own holder at the provider (the identity with the
local name after it) and rotates apart from the others. The plain shape is
unchanged and every existing row is the credential it was (novox/hq 04-ISSUES/069,
ADR 0094).
