Nomad changes

docs/snippets/dart/plugins/pdf_only_processor.md

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+<!-- snippet:skip reason="Dart cannot construct the opaque BoxFn closure types required by createPostProcessorDartImpl — flutter_rust_bridge generates them as RustOpaqueInterface with no Dart-side wrapper. The ProcessingStage enum is also not surfaced. Custom post-processors must be written in Rust." -->
+```dart title="Dart"
+import 'package:kreuzberg/kreuzberg.dart';
+
+Future<void> main() async {
+  // A Dart implementation of the `PostProcessor` trait that gates on PDF
+  // MIME type cannot be plugged into the global registry.
+  // `Kreuzberg.registerPostProcessor(impl)` exists, but its
+  // `createPostProcessorDartImpl` factory takes opaque `BoxFn*` closure
+  // values plus a `BoxFnDartFnFutureProcessingStage` whose constructors are
+  // not surfaced through flutter_rust_bridge. The `ProcessingStage` enum is
+  // not exported to Dart either.
+  //
+  // Implement the post-processor in Rust as `Plugin + PostProcessor` and
+  // register it via `register_post_processor` in a Rust shim crate.
+}
+```