Async function declared in `$derived()` results in `HierarchyRequestError` on hydration from SSR

[hmnd]

Describe the bug

It seems that #16806 introduced a regression for traditional {#await} blocks. Calling an async function declared with $derived results in hydration from SSR failing catastrophically.

Reproduction

On StackBlitz due to specifically happening in hydration

Logs

Uncaught (in promise) HierarchyRequestError: Failed to execute 'appendChild' on 'Node': This node type does not support this method.

System Info

System:
    OS: Linux 5.0 undefined
    CPU: (8) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
    Memory: 0 Bytes / 0 Bytes
    Shell: 1.0 - /bin/jsh
  Binaries:
    Node: 20.19.1 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 10.8.2 - /usr/local/bin/npm
    pnpm: 8.15.6 - /usr/local/bin/pnpm
  npmPackages:
    svelte: 5.39.4 => 5.39.4

Severity

blocking an upgrade