Header presence policy: which facets a request carries, from its identity,
endpoint family and explicit features only, plus the state facts it renders —
the process start and the presented build's wire facts. It never sees raw
headers, URLs or session state (the edge normalizes those into the three
request dimensions) and never renders values (the providers in facets.ts
do). Every header family's presence, the zero-rating pair included, is a
facet selection here; a provider returns undefined only when the state it
renders a value from does not exist.
Header presence policy: which facets a request carries, from its identity, endpoint family and explicit features only, plus the state facts it renders — the process start and the presented build's wire facts. It never sees raw headers, URLs or session state (the edge normalizes those into the three request dimensions) and never renders values (the providers in
facets.tsdo). Every header family's presence, the zero-rating pair included, is a facet selection here; a provider returnsundefinedonly when the state it renders a value from does not exist.