pub type LookupKey = (PlaceholderType, String);Expand description
Flat key for the resolver’s lookup table.
Phase 1 deliberately stays resource-shape-agnostic: callers supply a
flat (type, key) -> value map and the resolver doesn’t know whether
it came from a resource-local namespace, a field-level namespace, or
the globals.custom scope. Phase 2+ wiring composes the table from
the right places per RFC §2.2.