Adopt the validation-rules discipline that every public type is either
validated or excluded, enforced mechanically rather than by review. A new
gate enumerates the public surface from the compiler symbol graph and
fails the build, naming the type, if any public type is missing from the
coverage manifest or any manifest entry is no longer public.
scripts/validation-coverage.tsv classifies all 58 public types: the value
models with the mapping-key-uniqueness runtime invariant are validated,
and the namespaces, closed sum types, data-transfer values, error types,
and engine machinery are excluded with a one-line reason each. The gate
runs in check-all.sh and CI; a planted unclassified type was confirmed to
fail it.
This is the coverage-first phase of moving the validation layer to the
type-directed Validation idiom; the framework backing the validated
entries, the de-duplication of the Tagged validator machinery, and the
exhaustive tests follow.
