Svelte 5: State mutations in $effect breaks $derived

[ampatspell]

Describe the bug

If $state and $derived are class fields and state is modified in $effect, $derived doesn't update.

<script lang="ts">
  type ModelProps = {
    name: string;
  }

  class Model {
    data = $state<ModelProps>();

    constructor(data: ModelProps) {
      this.data = data;
    }

    name = $derived(this.data?.name);

    toggle() {
      this.data!.name = this.data!.name === 'zeeba' ? 'neighba' : 'zeeba';
    }
  }

  let model = $state<Model>(new Model({ name: 'zeeba' }));
  let shouldCreate = $state(false);

  $effect(() => {
    if(shouldCreate) {
      model = new Model({ name: 'zeeba' });
      untrack(() => {
        shouldCrete = false;
      });
    }
  });

  // this breaks also non-effect case
  // $inspect(model.data, model.name);
</script>

Reproduction

https://svelte-5-preview.vercel.app/#H4sIAAAAAAAAE52UTWvcMBCG_8pUBGzDZt0WevHaDoX2GCi00EPdg2LLjohWMtbsJlvj_15kSf7YbBrSk-XRzDOjd0bqSc0F0yT51RNJ94wk5HPbkg3BU2t-9JEJZGRDtDp0pbGkuux4iyCobLKCoC5IXkgAvm9Vh9DDQWJHywcYoO7UHgKLCHaFNG6GC7eqYuJbp1oNGfTGDGCyJ6Cx47LZWZPNuTIOllIKqrXF-PiKIoUMrjRSZOmcIQ8jkxoLtH6lkhq7Q4mqC01Msqgm8jAAvOd665jm40py-W25Jl3FOn5kVTj532zNVrQ6wguOdjPaeSaqphEsvFTFu61L-MySZRD8YeyOBnADgWS8uTfrxFvnwl31BQqGsB-1W-uVh5I9WjnC3jXEUTZTMwIuOXIqAhgiX7oBaoa3jhmuGxdBlpsjmR4YT8meEDJ4NRcMvnO-WBO5HANLY5X-znA6S1hToSdVr1hdsxLD0FdhxOB16MMWYvsThIGNCXwTwc_0mjKOwZx9TDtFDNFK-DOlfnK8_zomMXItoQsgdgfLG9bBX3jHShSn89C5_mr0cPUvtLIDdh43qrv1w7dbDEocj_MGdx2jDxqo0AqkktdWHyipZsY7juGKS90anS3MDOjGgf11SGP7cuSGnVb8aG9xVpCWNsy9Iiu7ZiVyJd3W2WanHguSp3cHRCVByVLw8iHrV-IO-fdp1LkEW3Ya25g8jSt-fBvaS78EV87231yr_JD_sN2ZFRylu4D1qwJflMvcmgu53UOIBpz1c38GFzGB_xk91eYRk-FtHHvNPcT-PSP41WSRqcaTYKMSWzM6fo5bWlVcNgl8eN8-udtXcd0KekqgFszbzPLado0rmUCpxGEv3WZD2wQ-zoCtU3W-9JeQr0Ad9tNE9a9xGvuzkA3Zq4rXnFUkMTd_-D38BfccLm-dBwAA

Logs

No response

System Info

System:
  OS: macOS 14.2.1
  CPU: (8) arm64 Apple M1
  Memory: 110.77 MB / 8.00 GB
  Shell: 5.9 - /bin/zsh
Binaries:
  Node: 18.19.0 - ~/.nvm/versions/node/v18.19.0/bin/node
  Yarn: 1.22.21 - ~/.nvm/versions/node/v18.19.0/bin/yarn
  npm: 10.2.3 - ~/.nvm/versions/node/v18.19.0/bin/npm
  bun: 1.0.15 - ~/.bun/bin/bun
  Watchman: 2023.12.04.00 - /opt/homebrew/bin/watchman
Browsers:
  Chrome: 122.0.6261.129
  Safari: 17.2.1
npmPackages:
  svelte: ^5.0.0-next.80 => 5.0.0-next.80

Severity

blocking all usage of svelte

[dummdidumm]

To reproduce:

1. click "Set model in effect"
2. click "Toggle model.data.name"

Hunch: Something about unowned signals