ThingDomain.Present and Items; every constructor, factory and key builder passes each non-nullable
reference parameter through Present (refusal names the slot, never a value) and each list through
Items (a private read-only copy, nil items refused). Lists are IReadOnlyList on every type.
TextInputNode's slot 2 property and parameter are InputKind, matching Rust input_kind.
Tests: NilPositionTests reads the Rust vector row by row; PresenceTests and ReadOnlyListTests
walk every door by reflection; InputKindNameTests. NameSetTests and the unit-arm rewrite follow.
Unit-arm statics are still present in this commit.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
ee80246cd0