Async Render bug 5.43.0

[timc13]

Describe the bug

If a query is awaited before initializing a tanstack-form, a render error occurs. If the query is awaited in the markup, it seems fine. However for my use case, I need the data from the awaited query to initialize a tanstack form.

Reproduction

StackBlitz

There are 2 workarounds

1. Do not await the query in script , and instead await it in the markup. This unfortunately does not work for my use case, as I want to use the query data to set the default values for the form
2. Downgrade to svelte@5.42.3

Logs

TypeError: Cannot read properties of undefined (reading 'Field')
    at eval (src/routes/+page.svelte:120:10)
    at Renderer.child (node_modules/svelte/src/internal/server/renderer.js:194:18)
    at Renderer.component (node_modules/svelte/src/internal/server/renderer.js:219:22)
    at _page (src/routes/+page.svelte:19:13)
    at eval (.svelte-kit/generated/root.svelte:74:7)
    at eval (src/routes/+layout.svelte:27:4)
    at Renderer.child (node_modules/svelte/src/internal/server/renderer.js:194:18)
    at Renderer.component (node_modules/svelte/src/internal/server/renderer.js:219:22)
    at _layout (src/routes/+layout.svelte:17:13)

System Info

System:
    OS: macOS 26.1
    CPU: (10) arm64 Apple M4
    Memory: 486.17 MB / 32.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 25.1.0 - /Users/timchen/.proto/tools/node/25.1.0/bin/node
    npm: 11.6.2 - /Users/timchen/.proto/tools/node/25.1.0/bin/npm
  Browsers:
    Chrome: 142.0.7444.60
    Firefox: 144.0.2
    Safari: 26.1
  npmPackages:
    svelte: 5.42.3 => 5.43.0

Severity

blocking an upgrade

[timc13]

Uncertain, but this might be the same issue as #17090

[sillvva]

It might be related, but #17120 (which is assigned to close #17090) doesn't fix it.