[Bug]: Trivial dependency cycles are not detected, neither output nor errors produced

Component

Reactive Programming

Severity

P1 - High (major feature broken)

Shiny Version

1.4.0

Python Version

3.10.12

Minimal Reproducible Example

from shiny.express import input, render, ui


@render.express
def myrender():
    ui.input_select("sel", None, ["All", "So", "Much"], selected="All")
    input.sel()
    "Sadly, we never get here - silently. Poor user will never know why."
    "Actually, nothing is rendered at all."

Behavior

The code above produces no rendered output and no error messages. This can hardly be called "transparent reactivity" (re: https://shiny.posit.co/py/docs/overview.html#reactivity ), as nothing there is transparent.

Expected behavior:
Complexity of dealing with circular dependencies (detecting, and whenever possible, avoiding in a manner of least user surprise) is understood. Yet, apparently, would be nice to do something about such cases.

Error Messages (if any)

None!

Environment

Ubuntu
Chromium 126

Start by running the minimal reactive example from the issue and trace the reactive rendering path responsible for the silent failure. The payload names no source files or tests, so first locate the cycle-detection or dependency-resolution entry point; done should include a regression test and a defined user-visible result for this cycle.