Remote Functions: timeouts and retries

Describe the problem

Derived from discussions:

• https://github.com/sveltejs/kit/discussions/13897#discussioncomment-13673002
• https://github.com/sveltejs/kit/discussions/13897#discussioncomment-13594549

Sometimes users on a slow or distant connection cannot complete a request roundtrip from the browser to the server, and in some cases a retry would save the user time while designers can provide feedback for the delayed response.

Or, a user may become briefly offline and the outgoing remote functions need a way to replay once the user is online again.

Describe the proposed solution

A combination of solutions could be helpful:

1. Expose a per-function config to pass in an AbortController to manually time out requests, and a retry count to retry the request upon error, and a timeout number in milliseconds for how long to wait before the next retry.
2. Expose a universal config for all functions to time out after a set number of milliseconds.
3. Expose the underlying fetch for remote functions, or allow a passed-in fetch instance to support preconfigured options.

Alternatives considered

Handle errors and retries in userland without convenience options:

<script>
  import { getItems } from './data.remote'

  // in lieu of `getItems({ retries: 2 })` or equivalent

  let getItemsRetryCount = $state(2)

  $effect(() => {
    // TODO: this is flawed logic, but the intent is to call this effect
    // whenever a remote function completes
    if (!getItems().error || getItemsRetryCount <= 0) return

    getItems().refresh()
    getItemsRetryCount--
  })
</script>

<svelte:boundary>
  <!-- pending and error snippets for initial data representations -->
  <!-- if I had them! -->

  {#if getItems().error && getItemsRetryCount > 0}
    Retrying...
  {:else if getItems().error}
    Server error, please try again in a few minutes. <button onclick={() => getItems().refresh()}>Try again</button>
  {:else if getItems().loading}
    Loading...
  {:else if getItems().ready}
    <ul>
    {#each getItems().current as item}
      <li>{item}</li>
    {/each}
    </ul>
  {/if}
</svelte:boundary.

Importance

would make my life easier

Additional Information

No response

Start by reviewing the two linked discussions and the remote-functions behavior described in this issue. Determine whether timeout, retry, AbortController, offline replay, and custom fetch support can share a coherent configuration model. Done means the scope, API behavior, and acceptance criteria are settled; no implementation files or tests are named here.