After upgrading to the latest Astro (>=5.15.9), all SVG images stopped displaying.

Issues found:

• With passthroughImageService enabled, SVG images return Content-Type: image/null and fail to render (JPG works).

After downgrading Astro, the regression starts at 5.15.9.
Related issues:

• passthroughImageService() does not prevent WebP conversion for Image component in Astro 5.15.2 #14721: images incorrectly converted to WebP
• fix: passthroughImageService generate webp #14776: introduced validateOptions in noop.ts to address it

delete newOptions.format; -> "Content-Type": mime.lookup(format) ?? `image/${format} -> Browser Content-Type: image/null -> image boom (svg)

Changes

I believe the issue in #14721 originates from the options.format = DEFAULT_OUTPUT_FORMAT assignment in service.ts.
To address this, I added a flag to prevent setting a default output format when the noop service is used.

Although my JPG images still return image/null (but browsers can display them), SVG images now work correctly.

before:

after:

Testing

I wasn’t sure how to write it.

Docs

There shouldn't be much to change. This aligns better with the note in #configure-no-op-passthrough-service
stating that Note that Astro does not perform any image transformation and processing in these environments.