Dashboard: bslib::value_box() ignores `#| expandable: false` and shows Expand button

[mcanouil]

I have:

• searched the issue tracker for similar issues
• installed the latest version of Quarto CLI
• formatted my issue following the Bug Reports guide

Bug description

In a format: dashboard document, a cell that outputs a bslib component such as bslib::value_box() shows an "Expand" (full-screen) button in the bottom-right corner even when the cell sets #| expandable: false. A Quarto-native value box, or a plain plot(), correctly honours the option and shows no button.

Reported in discussion #14714. Root cause traced below.

Steps to reproduce

---
format: dashboard
---

## Column

```{r}
#| expandable: false
bslib::value_box(title = "x", value = 1, theme = "primary")
```

Actual behavior

The value box renders with an "Expand" button; #| expandable: false has no effect.

Root cause (against v1.9.38, SHA 6ebb5db80eb542ac76189c3d7c33ae6f654b93d2):

1. When a cell outputs raw bslib- HTML, dashboard.lua captures it into bslibRawOutputs and re-emits it "unharmed". The cell's card options are read via readOptions(el)/makeCard(...) but applied only to the remaining non-bslib content, so #| expandable: false never reaches the value box and no data-expandable attribute is emitted on it.

   • quarto-cli/src/resources/filters/quarto-post/dashboard.lua

     Lines 292 to 304 in 6ebb5db

     	if #bslibRawOutputs > 0 then
     	-- If bslib outputs were detected, we need to elevate those rawblocks and
     	-- just allow them to pass through the system unharmed along side
     	-- the cell and any of its other output
     	local result = pandoc.Blocks(bslibRawOutputs)
     	if el ~= nil and #el.content > 0 then
     	local options, userClasses = dashboard.card.readOptions(el)
     	local card = dashboard.card.makeCard(el.content, userClasses, options)
     	if card ~= nil then
     	result:insert(card)
     	end
     	end
     	return result

2. In HTML post-processing, processCards handles every .card, including the bslib value box. With no data-expandable attribute present, defaultValue decides: it suppresses the button only for elements with Quarto's own class kValueboxClass ("valuebox") or a flow layout. A bslib value box uses bslib-value-box, so the check misses and the fallback returns dashboardMeta.expandable, which defaults to true, injecting Quarto's own Expand button (kExpandBtnHtml).

   • quarto-cli/src/format/dashboard/format-dashboard-card.ts

     Lines 82 to 101 in 6ebb5db

     	attr: kAttrExpandable,
     	handle: (el: Element, attrValue: string) => {
     	if (attrValue !== "false") {
     	const shellEl = doc.createElement("DIV");
     	shellEl.innerHTML = kExpandBtnHtml;
     	for (const childEl of shellEl.children) {
     	el.appendChild(childEl);
     	}
     	el.setAttribute(kAttrFullScreen, "false");
     	}
     	},
     	defaultValue: (el: Element) => {
     	if (el.classList.contains(kValueboxClass) || hasFlowLayout(el)) {
     	return "false";
     	} else {
     	return dashboardMeta.expandable ? "true" : "false";
     	}
     	},
     	},
     	{

   • quarto-cli/src/format/dashboard/format-dashboard-shared.ts

     Line 53 in 6ebb5db

     export const kValueboxClass = "valuebox";

Because the button is Quarto's, passing full_screen = FALSE to bslib::value_box() does not remove it.

Expected behavior

#| expandable: false on a cell that outputs a bslib::value_box() (or any bslib card) should suppress the Expand button, matching the behaviour of Quarto-native value boxes.

Your environment

• OS: Ubuntu 24.04
• bslib: 0.11.0.9000

(Environment as reported in discussion #14714.)

Quarto check output

Quarto 1.9.38 (as reported in discussion #14714). Root cause verified against source at tag v1.9.38 and reproduces on main. Full quarto check output was not provided by the original reporter.