Describe the bug

When using {#if await ...}{:else}{/if} blocks with SvelteKit remote functions (query from $app/server), a layout shift occurs during hydration despite both branches being prerendered on the server. Using two separate {#if} blocks instead of {:else} eliminates the layout shift. This issue only occurs with remote functions, not with regular async functions or promises.

Reproduction

Remote functions (test.remote.ts)

import { query } from "$app/server";

export const getTest1 = query(async () => {
  return false;
});

export const getTest2 = query(async () => {
  return "Hello World! 2";
});

Case 1: With layout shift (using :else)

<script lang="ts">
    import { getTest1, getTest2 } from "./test.remote";
</script>

{#if await getTest1()}
  Testing
{:else}
  {await getTest2()}
{/if}

<h1>Welcome to SvelteKit</h1>
<p>Visit <a href="https://svelte.dev/docs/kit">svelte.dev/docs/kit</a> to read the documentation</p>

Case 2: Without layout shift (using separate {#if} blocks)

<script lang="ts">
    import { getTest1, getTest2 } from "./test.remote";
</script>

{#if await getTest1()}
  Testing
{/if}
{#if !await getTest1()}
  {await getTest2()}
{/if}

<h1>Welcome to SvelteKit</h1>
<p>Visit <a href="https://svelte.dev/docs/kit">svelte.dev/docs/kit</a> to read the documentation</p>

Expected behavior

Both approaches should render identically during SSR and hydrate without layout shifts. The {:else} block should produce the same hydration result as using two separate conditional blocks with inverse conditions when using remote functions.

Actual behavior

• Case 1 (with :else): Causes visible layout shift during hydration
• Case 2 (separate {#if} blocks): No layout shift, smooth hydration
• Important: This only happens with remote functions from $app/server, not regular promises

Reproduction

https://github.com/timootten/SvelteKit-Layout-Shift

Logs

System Info

System:
    OS: Windows 11 10.0.26100
    CPU: (16) x64 AMD Ryzen 7 5700X 8-Core Processor
    Memory: 17.35 GB / 31.91 GB
  Binaries:
    Node: 22.20.0 - C:\Program Files\nodejs\node.EXE
    npm: 10.9.0 - C:\Program Files\nodejs\npm.CMD
    pnpm: 10.18.1 - C:\Users\timoo\AppData\Local\pnpm\pnpm.CMD
    bun: 1.3.4 - C:\Users\timoo\AppData\Local\pnpm\bun.CMD
    Deno: 2.3.3 - C:\Users\timoo\.deno\bin\deno.EXE
  Browsers:
    Chrome: 143.0.7499.40
    Edge: Chromium (140.0.3485.54)
    Firefox: 144.0.2 - C:\Program Files\Mozilla Firefox\firefox.exe
    Internet Explorer: 11.0.26100.1882
  npmPackages:
    @sveltejs/adapter-node: ^5.4.0 => 5.4.0
    @sveltejs/enhanced-img: ^0.9.2 => 0.9.2
    @sveltejs/kit: https://pkg.pr.new/sveltejs/kit/@sveltejs/kit@966e232 => 2.49.1
    @sveltejs/vite-plugin-svelte: ^6.2.1 => 6.2.1
    svelte: 5.45.6 => 5.45.6
    vite: ^7.2.6 => 7.2.6

Severity

annoyance

Additional Information

No response