Raised when a read model's shape, or the requested stream scope, is not safe to guard a decision with.

:reason mirrors the C# client's DecisionReadRefusalReason:

• :reducer — the model is produced by an actively-observed reducer. Only a passive reducer (use Chronicle.Reducers.Reducer, active: false) can back a decision read.
• :join — the projection declares join/2 or removed_with_join/2. A joined read can change from an event outside the guarded event source, which the guard cannot express.
• :hierarchy — the projection declares children/2. Nested/child collections are not representable as a single concurrency scope.
• :not_event_log — the read model does not project from "event-log" (an :event_sequence override), or is not a recognized read model/reducer at all.
• :open_ended_event_types — the projection declares from_every/1: it would have to guard against every event type ever appended, which Chronicle's ConcurrencyScope cannot express.
• :no_event_types — the admitted shape resolves to no event types at all.
• :not_event_source_keyed — a from/removed_with clause declares a :key other than the default "$eventSourceId" (a composite key, an event-context key, or similar).
• :unsupported_event_type_id — one of the model's event type ids contains a comma, which cannot be told apart from an id list on the wire.
• :all_streams_not_supported — a stream-scoped read was asked for the default stream (an empty or "All" event stream type) instead of a specific one.
• :stream_scope_not_supported — the kernel reported the read model instance as not stream-scoped (StreamScoped: false), so a stream-scoped guard cannot be built from it.
• :fold_incomplete — after 3 attempts, the read model still had not caught up to events already visible for its key/types; the read could not be made deterministic.