Widgets don't load sometimes

[wch]

With this example app, the slider sometimes shows up and sometimes doesn't. I think it's possible that there's some sort of timing issue. Is it possible that it's trying to render the widget before some of the relevant JS code has been initialized?

[cpsievert]

Probably a duplicate of #36

[cpsievert]

This should be fixed now

[cpsievert]

This issue has re-surfaced (and can be replicated consistently with shiny run examples/outputs/app.py -- note how the widget doesn't render on initial load) since py-shiny's JS no longer includes rstudio/shiny#3635