Introduce readers as a fourth cross-feature mechanism alongside events,
jobs, and realtime. Readers solve synchronous domain queries across
verticals (e.g. permission checks) where Payload relationTo gives raw
data but the answer requires business-rule evaluation by the owning
feature.
- Define rules Q0-Q3 (query-only, contract public, read-only, no cycles)
- Reader wraps existing use cases via ReadOnly<F> brand enforcement
- Lives under integrations/readers/ with ./reader export subpath
- Manifest reads: ["auth"] field for conformance gate visibility
- Update glossary with Reader, reads, ReadOnly<F> terms
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