Handle SvelteKit data preloads

[Lms24]

Description

SvelteKit provides strategies to preload data for another page when

• [default] hovering over a link to a page
• tapping/onotuchstart/onmousedown a link to a page

If any of these strategies are enabled (which they are by default), we miss the client-side http.client fetch spans, if the linked page has a server-only load function, because fetch spans are only started if there is a parent span.

The expected parent span would be the navigation span but this one does not exist because the kit router only starts the navigation when actually handling the link click.

Worth noting, we still propagate the trace to the backend, however, in this case the one of the current traceId. Which is probably fine because the really isn't an alternative.

We should ensure that we do start a fetch span for this preload.

Options:

• start artificial parent span (if possible)
• override onlyIfParent for this fetch request (if possible)
• do nothing and wait for EAP/span streaming