MCP file selection

File selection is explicitly opt-in. Lurq does not intercept rfd, open an OS chooser, read files, validate formats, add filename extensions or perform saves. Adapt the same handler used by the normal UI: it either awaits the broker or uses its existing native picker. Never launch both.

let dialogs = lurq::mcp::FileDialogBroker::new();
let mcp = tree.enable_mcp(
  lurq::mcp::McpConfig::new()
    .scope(lurq::mcp::Scope::custom("file_dialogs"))
    .file_dialogs(dialogs.clone()),
);
// Give dialogs to the component owning the normal Open button.
// Obtain the actual window handle from ctx.window() in that component.

An adapted native handler, using the application’s existing rfd dependency:

async fn pick_design(
  dialogs: &lurq::mcp::FileDialogBroker,
  window: &lurq::app::WindowHandle,
) -> Result<Option<std::path::PathBuf>, lurq::mcp::FileDialogError> {
  use lurq::mcp::{FileDialogError, FileDialogOperation, FileDialogRequest};
  let mut request = FileDialogRequest::new(FileDialogOperation::OpenFile);
  request.title = "Open design".into(); // Use the embedding app's localized copy.
  request.filters = vec![("Design".into(), vec!["kontur".into()])];
  match dialogs.request(window, request)? {
    Some(pending) => match pending.await {
      Ok(selection) => Ok(selection.paths.into_iter().next()),
      Err(FileDialogError::Cancelled) => Ok(None),
      Err(error) => Err(error), // Revocation must NOT launch a native picker.
    },
    None => Ok(rfd::AsyncFileDialog::new()
      .add_filter("Design", &["kontur"])
      .pick_file().await.map(|file| file.path().to_owned())),
  }
}
// The existing handler next checks its captured document/session, reads and
// validates the chosen file, and uses its ordinary transactional admission.

Without registration, request returns Ok(None) and native behavior is unchanged. Once registered, the broker cannot be registered again or revived after shutdown. Intercepted requests stay intercepted across scope changes; errors/cancel do not route them to native dialogs. Dropping the future removes the request immediately. Accepted window close, shutdown, denied dialog tools or scope/serving revocation cancel waiters. A vetoed close request does not cancel them.

With authentication and the file_dialogs scope granted, lurq_file_dialogs lists pending requests with unique request_id, canonical window (main or w<ID>), operation, advisory title/filters and optional suggested_name. No tools are added when no broker was registered. Use exactly that identity for lurq_file_dialog_respond:

{"request_id":"<UUID>","window":"main","operation":"open_file","action":"select","paths":["H:/designs/screen.kontur"]}

Cancel sends action: "cancel" without paths/overwrite. Select accepts one absolute path for open_file, open_folder or save_file, and 1–64 for open_files. Unknown/stale/duplicate IDs, wrong window epochs/operations, relative paths and incorrect cardinality are rejected without completing another request. Paths are not normalized. Request metadata/path lengths and 32 pending slots are bounded.

save_file selection requires an explicit Boolean overwrite. It is returned in FileDialogSelection as caller intent, not a toolkit claim that a file exists or replacement is safe. The app must enforce its own existence, permission, overwrite, stale-document and atomic-write/TOCTOU policy before saving. A false flag must not silently replace an existing file; a true flag is not permission to bypass app policy. Filters remain advisory and never replace content validation.

This SDK API cannot steer an unmodified application’s direct rfd calls. Native chooser visuals, OS ownership and real application import/export remain separate consumer integration checks. No process-global “next path” state or OS input automation is used.