Function editor_preview_open 

pub fn editor_preview_open(
    project: EditProject,
    state: State<'_, EditorPreviewState>,
) -> Result<(), String>

Open / update the live editor preview for project (AUT-510). Builds the wgpu compose pipeline + decode stream the first time (and when the source clip changes); otherwise updates the project so edits show on the next frame. Synchronous on purpose — the wgpu device is created on the Tauri command worker thread, never the webview/main thread.

Errors

Returns a message if the source can’t be opened or wgpu init fails.