ConverterIntrospector
Reads a converter declaration's ConverterShape from the KSP Resolver: its (S, T) type pair from the MapTypeConverter supertype — found by walking UP the superclass chain, so parameterized-converter bases (the ledger's official recipe: object PriceFormatConverter : FormattedDoubleStringConverter(digits = 2) where the abstract base extends MapTypeConverter<Double, String>) resolve too — and which directions it provides, via function-level detection of the declared overrides (most derived wins) and their @UnsupportedDirection annotations.
Generic-passthrough bases (Base<X> : MapTypeConverter<X, String>) are OUT OF SCOPE: resolving them would require type-argument substitution through arbitrary chains; they produce a guided compile error via logger instead.
Parameters
optional diagnostics sink; null disables the generic-passthrough error (introspection-probe tests construct the introspector without a logger).
Functions
True when converterFqn resolves to ANY class declaration — converter or not. Lets callers distinguish "reference does not resolve" from "resolves but is not a direct MapTypeConverter subtype" when shapeOf returns null.
Returns the ConverterShape for converterFqn, or null when the declaration cannot be resolved or does not extend MapTypeConverter
Returns the (S-FQN, T-FQN) pair of declaration's MapTypeConverter<S, T> ancestry, walking up the superclass chain, or null when the declaration never reaches the base (or binds it through an out-of-scope generic passthrough — diagnostic via logger). Public so @KMapperConfig discovery shares the exact same pair resolution.