Decides which MessageCodec carries a given type on and off the wire.

Nothing has to be registered. Any @Serializable type - including a parameterised one like List<OrderEvent> - is serialized as JSON with the Json configured by Builder.configureJson, resolved from the type at the call site. The registry is an override table: it holds the built-in text and binary codecs, plus whatever a codecs { } block registers for types that need something other than JSON.

Resolution, in order:

• an exact type match among the overrides - this is what carries a registration for a parameterised type, since List<A> and List<B> are different keys;

• for a type with no type arguments, a match on the classifier alone (see below);

• a JSON codec derived from the type's serializer, or NatsyMissingCodecException if it has none.

Why step 2 exists. typeOf<T>() is sensitive to flexibility: a T inferred from a value a Java method returned is a platform type (String!), and its KType is not equal to typeOf<String>() - kotlin.jvm.internal.TypeReference.equals compares the platform-type upper bound. Without step 2, kv.put("audit", ack.stream) would miss StringCodec and write a JSON-quoted string. With no type arguments and T : Any ruling out a nullable top level, the classifier determines the codec, so this step is exact rather than a fallback - it cannot serve a codec for some other type, which is the hazard an erased lookup would reintroduce.

An override is matched by type, not by assignability: registering a codec for Foo says nothing about List<Foo>, which still goes through JSON. That is deliberate - see codecForType.