Thrown by onIntegrationEvent's wrapper when a delivered message is refused before the application handler runs. One class rather than four keeps the consumer's instanceof branch a single import, while reason discriminates.

The message carries the whole diagnostic on its own — the reason, the topic, and the expected against the observed type/version — because the default in-memory composition's dispatch reporter flattens a rejection to error.message in one log string, so on that path the structured fields never reach an operator and the message is all that survives. The fields serve an application's instanceof branch on a path that surfaces the error object itself (a real broker's nack handler, or a bespoke sink on the 'custom' broker arm).

For reason: 'parse', the thrown parser error is carried as cause — a schema error's field paths are the most useful diagnostic in the whole path. The field is typed unknown and set verbatim: a parser that throws a non-Error value (a string, most commonly) is preserved as-is, and the rejection's own message still names the topic and reason without it.