[Bug]: Uncaught TypeError in _shinyResizeObserver.ts when dynamic components/modals are removed

Component

UI (ui.*)

Severity

P2 - Medium (workaround exists)

Shiny Version

1.6.1+

Python Version

3.12

Minimal Reproducible Example

from shiny import App, render, ui
import matplotlib.pyplot as plt

app_ui = ui.page_fluid(
    ui.input_action_button("open_modal", "Open Modal with Plot"),
)

def server(input, output, session):
    @render.plot
    def my_plot():
        fig, ax = plt.subplots()
        ax.plot([1, 2], [3, 4])
        return fig

    @input.open_modal
    def _():
        ui.modal_show(
            ui.modal(
                ui.card(
                    ui.card_header("Card inside Modal"),
                    ui.output_plot("my_plot"),
                ),
                title="Reproduction Modal",
                easy_close=True
            )
        )

app = App(app_ui, server)

Behavior

When a container that is registered with the ShinyResizeObserver (such as a card, sidebar, or a layout component inside a modal) is removed from the DOM, the observer does not automatically stop watching it.

During the cleanup/removal transition:

1. The DOM elements are detached/unbound, which clears their associated jQuery data (shinyOutputBinding).
2. The browser triggers a final ResizeObserver callback on the resizing/disappearing container.
3. The callback runs query selectors inside the target for .shiny-bound-output and finds the detached elements.
4. Because the elements are detached/unbound, calling $(el).data("shinyOutputBinding") returns undefined.
5. Destructuring binding and onResize from undefined throws an uncaught JavaScript error, halting the client-side execution.

Proposed Solution

It seems like the underlying issue is actually in bslib.

A defensive check or fallback should be added in _shinyResizeObserver.ts to safely ignore elements whose bindings have already been torn down or are not yet set:

const outputData = $(el).data("shinyOutputBinding");
if (!outputData) return;
const { binding, onResize } = outputData;
if (!binding || !binding.resize) return;

Or using a fallback:

const { binding, onResize } = $(el).data("shinyOutputBinding") || {};
if (!binding || !binding.resize) return;

Disclaimer: This Bug Report was prepared with the help of Antigravity and manually verified.
I greatly appreciate all the hard work the maintainers have poured into the shiny ecosystem and would not like to add AI slop here 😅

Error Messages (if any)

Uncaught TypeError: Cannot destructure property 'binding' of '$(...).data(...)' as it is undefined.
    at _shinyResizeObserver.ts:81:21
    at NodeList.forEach (<anonymous>)
    at ResizeObserver.<anonymous> (_shinyResizeObserver.ts:78:12)

Environment

Python package: shiny (version 1.6.0 / 1.6.1+)
Underlying UI package: bslib (frontend assets compiled from rstudio/bslib version 0.10.0 / 0.11.0+)

OS: Win10
Browser: Edge 149.0.4022.69

Start with the minimal Python reproduction and inspect _shinyResizeObserver.ts around line 81, where the ResizeObserver callback reads shinyOutputBinding data. Reproduce opening and removing the modal, then verify that cleanup no longer produces an uncaught TypeError when detached outputs are encountered.