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docs/snippets/dart/plugins/embedding_backend.md

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+<!-- snippet:skip reason="Dart cannot construct the opaque BoxFn closure types required by createEmbeddingBackendDartImpl — flutter_rust_bridge generates them as RustOpaqueInterface with no Dart-side wrapper. Custom embedding backends must be written in Rust." -->
+```dart title="Dart"
+import 'package:kreuzberg/kreuzberg.dart';
+
+Future<void> main() async {
+  // A Dart implementation of the `EmbeddingBackend` trait cannot be plugged
+  // into the global registry. `Kreuzberg.registerEmbeddingBackend(impl)`
+  // exists, but its `createEmbeddingBackendDartImpl` factory takes opaque
+  // `BoxFn*` closure values whose constructors are not surfaced through
+  // flutter_rust_bridge.
+  //
+  // Implement the backend in Rust as `Plugin + EmbeddingBackend` and register
+  // it via `register_embedding_backend` in a Rust shim crate.
+}
+```