[Bug]: session.on_flushed callbacks do not trigger messages being sent to client

[jcheng5]

Component

Reactive Programming

Severity

P2 - Medium (workaround exists)

Shiny Version

1.3.0

Python Version

Any (including pyodide)

Minimal Reproducible Example

shinylive

from shiny.express import input, render, ui, session

ui.input_text("foo", "Foo")

@session.on_flushed
def _():
    ui.update_text("foo", value = "Flushed")

Behavior

In the example above, ui.update_text() is called, but because it's part of an on_flushed, it doesn't actually get sent to the client. (If the app had some other outputs/effects, then the next time a flush naturally occurred, then the update_text would take effect.)

Here's the same example in R, which doesn't exhibit the problem.

Error Messages (if any)

Environment

shinylive.io