Can't save shortcode returned value to a block `set`

[pmpinto]

Operating system

macOS 15.5

Eleventy

2.0.1

Describe the bug

This is empty:

{% set photoData %}
  {% image
    photo.data.file,
    photo.data.description,
    '100vw',
    'photo',
    true,
    'object'
  %}
{% endset %}

<pre>{{ photoData }}</pre>

This returns the JSON object I wanted:

<pre>
{% set photoData %}
  {% image
    photo.data.file,
    photo.data.description,
    '100vw',
    'photo',
    true,
    'object'
  %}
{% endset %}
</pre>

Reproduction steps

There quite a few moving parts, but I'll try to keep this simple.

I have an image shortcode defined in my .eleventy.js:

eleventyConfig.addShortcode('image', async (src, alt, sizes, className, lazyLoad, returnAs) => Tags.image(src, alt, sizes, className, lazyLoad, returnAs));

This Tags.image() function ends with:

if (returnAs === 'html') {
  return Image.generateHTML(metadata, imageAttributes)
} else if (returnAs === 'object') {
  return JSON.stringify(Image.generateObject(metadata, imageAttributes))
}

Invoking the {% image %} shortcode directly does return the JSON string I'm looking for. But for some reason, if I try to save it to a variable with a block set, it returns nothing.

Expected behavior

I would expect both scenarios under "describe the bug" to output the same result.

Reproduction URL

No response

Screenshots

No response