//! The projection facts a target needs, derived from the IR and owned by no
//! backend.
//!
//! [`crate::name`] is the precedent and the reason: the pinned name transform
//! lives in `ridl-ir` because it is a projection — a pure function from IR
//! identity to a target's shape — and because `ridl-ir` is the crate every
//! consumer of a projection already depends on. The same holds for the facts
//! below. `ridl-backend-flatbuffers` emits the `.fbs` schema from them,
//! `ridl-backend-rust` emits the payload codec from them, and `ridl-descriptor`
//! reads the same size bound for the catalog descriptor. None of those three
//! may depend on either of the other two, so the facts cannot live in a
//! backend.
//!
//! One submodule per target. [`flatbuffers`] reads ADR-0019's projection rules
//! once, for both of the emitters that have to agree on them. [`proto3`] holds
//! ADR-0017's scalar table once, for the `.proto` emitter and for [`size`].
//! [`size`] states the maximum encoded size of a payload under each of those
//! two encodings, over both of them; it is the one sizer, and the catalog
//! descriptor and the codegen model both read it.