The tagged-node validator carried its own copy of the validation machinery:
a Tagged.Rule cloning Validation's check type and a Tagged.Context cloning
its context, differing only in subject type. That is the per-layer
duplication the validation idiom exists to prevent (principle 10).
Generalise the type-directed framework over both the subject and the
document: SubjectContext, Check, and AnyCheck now take a Document type
parameter for the validated tree's root. The model layer validates with a
Model.Value document, the tagged layer with a Tagged.Node document, each
truthful rather than forcing one root type to stand in for the other.
The tagged layer keeps only what is genuinely its own: the Node document
type, its built-in check (now Tagged.BuiltinCheck, a Check<Node, Node>), and
its traversal. Tagged.Rule and the tagged Context are removed. The validator
surface is unchanged but validating now takes a Check<Node, Node>.
All 399 tests pass; the coverage gate reconciles to 62 public types.
Add the declarative combinators the validation idiom composes rules from,
as free functions returning closures: comparison operators (==, !=, <, <=,
>, >=) lifting a key path and a literal into a predicate; take to dig to a
value and run arbitrary logic; all to apply many checks to one context; lift
to run child-typed checks against a value reached by key path; and && / ||
to compose two checks (concatenating their errors, or short-circuiting so
errors surface only when both fail). Both the context-rooted and
subject-rooted key-path forms are provided so an author can pin the subject
type in either clause.
A key path is immutable and read-safe but not declared Sendable, so a
@Sendable predicate captures it through a small @unchecked Sendable box.
lookup is omitted: it resolves references against a component store the
generic model does not carry; a consumer with references supplies it.
Each combinator has a pure-function test against a hand-built context, per
the idiom's requirement to unit test the operators in isolation.
