slot/snippet and custom elements broken/usage unclear

[mspae]

Describe the bug

The usage of snippets (and slots) within custom elements is not clear from the documentation. The resulting order of DOM nodes is different between using a svelte component "normally" and as a custom element. I'm assuming this is unavoidable and due to the special nature of custom elements. However, the corresponding caveats for using slots/snippets within custom elements (assuming there some footguns lying around) are not documented on this page so I'm at a loss how to mitigate this issue.

I think this is probably the same issue as #12892 - the resolution of that issue ("use slots") is not clear to me. I'm probably missing something.

Reproduction

https://svelte.dev/playground/87c914a892664f7990bae0fa38290278?version=5.28.2

(Same thing using the @render syntax https://svelte.dev/playground/d9ae949baaea4276a6bd6edcdb03a451?version=5.28.2)

Logs

System Info

System:
    OS: Linux 6.1 Debian GNU/Linux 12 (bookworm) 12 (bookworm)
    CPU: (4) x64 Intel Core Processor (Skylake, IBRS)
    Memory: 7.04 GB / 7.75 GB
    Container: Yes
    Shell: 5.2.15 - /bin/bash
  Binaries:
    Node: 20.19.1 - /usr/bin/node
    npm: 10.8.2 - /usr/bin/npm

Severity

blocking all usage of svelte