11. Checkability is a property of the procedure, not of its capabilities

Context

requires records what a procedure needs from a language pack. It says nothing about whether the procedure can be checked at all, and the difference turned out to matter: sorting the catalogue by what the English pack already supplies produced 85 rows, of which roughly a quarter can never have a checker.

canada_dry is defined as having the manner of a constrained work with no constraint operating. found_poem, chance_operation and calligram have no computable acceptance criterion at all. A third group — anagram, cut_up, every_nth_word — is perfectly decidable, but only against the source text the work was made from, which check(text) had no room for.

Left alone, the coverage metric promised a gap that could never close.

Decision

Every catalogue row declares checkability: self when decidable from the text and its parameters, source when it needs the text it was made from, none when no computable acceptance criterion exists. Coverage is measured against the rows that are not none, and denckring status reports the unreachable count separately.

Source-relative procedures carry the source on a SourceParams base model, so check keeps its one-text signature and the requirement appears in params_schema() for callers that never touch Python.

An invariant fails the build if a registered procedure declares checkability: none — if a checker exists, the row was mis-filed.

Consequences

The project metric describes reachable work. A none row becomes an honest statement about a form rather than a backlog item, so the catalogue can survey the field without pretending every entry is pending implementation.

The invariant only catches one direction of error: a row wrongly filed none quietly shrinks the denominator and nothing complains. That list is about two dozen rows and should be read directly rather than trusted.

Classifying the catalogue this way immediately caught four rows whose requires had been wrong — boustrophedon is source-relative, and semordnilap, kangaroo_word, word_square and charade cannot be decided without knowing what counts as a word.