# `door` — from a declared grammar to a sealed expansion
A proc host converts tokens and preserves compiler spans, while each descriptor child owns the grammar and rendering for its projection.
This home owns the orchestration between those boundaries: an informed declaration enters, the generic request road runs, and either a sealed expansion or one typed diagnostic leaves.
## Authority crossing
Each helper road receives the captured body and the semantic item it exercises, the grammar selected by its caller, and the request door that names the caller's act.
The item is the declaration both projection and carrier requests stand over, while the body's independent helper identity reaches the final support assembly at the grammar's declared position.
Where a projection needs producer qualification, a physical dependency binding, or a second capture, that authority also arrives as declared input rather than being inferred here.
The descriptor child reads and renders its own meaning.
The request, diagnostic, support, and identity homes retain their own mints, so this home composes their public roads without restating their laws.
## Delivery postures
A carrier projection hands verified axes to the support home and returns an inert declaration-site carrier whose cargo remains behind the consumption boundary.
A direct projection returns ordinary declaration-site items without inventing a carrier it does not need.
The projection kind determines which posture applies, and this home does not flatten the two into one weaker representation.
## Composition
The proc crate calls these roads after capture and emits the expansion it receives, while a callable compiler user may invoke the same public roads directly.
The facade preserves those owning modules rather than adding another door vocabulary.
## Evidence ceiling
A successful road establishes that the declared projection completed the compiler's generic request sequence and produced a sealed expansion under the caller's stated authority.
It does not establish that a consumption target invokes a carrier, that generated code behaves correctly after compilation, or that any downstream harness judgment is true.
Those claims remain with the external compiler, proc, facade, generated-support, package, and target observations that exercise the resulting expansion.