Remote functions - `withOverride` optimistic updates require 2 ticks

[alexiglesias93]

Describe the bug

I'm implementing optimistic updates using remote functions, and while playing around with document.startWithTransition I've noticed that I need to wait 2 Svelte ticks for the transition snapshot to be taken correctly.

Not sure if this is expected or a bug!

Reproduction

Using the following example, waiting for a single tick will not guarantee that the DOM is updated after firing an optimistic update:

	const handle_delete_member = () => {
		document.startViewTransition(async () => {
			const override = get_members().withOverride((members) =>
				members.filter((m) => m.id !== member.id)
			);

			delete_member(member.id).updates(override).catch(console.error);

			await tick();
		});
	};

The view transition doesn't run correctly because I assume that the new snapshot doesn't contain the optimistic updates yet:

1.tick.mp4

But if I wait for 2 ticks, then the snapshot seems to be correct and the view transition runs as expected:

	const handle_delete_member = () => {
		document.startViewTransition(async () => {
			const override = get_members().withOverride((members) =>
				members.filter((m) => m.id !== member.id)
			);

			delete_member(member.id).updates(override).catch(console.error);

			await tick();
+			await tick();
		});
	};

2.ticks.mp4

Logs

System Info

System:
    OS: macOS 15.7.3
    CPU: (8) arm64 Apple M3
    Memory: 524.06 MB / 24.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 24.12.0 - /Users/alexiglesiaspinol/.nvm/versions/node/v24.12.0/bin/node
    npm: 11.6.2 - /Users/alexiglesiaspinol/.nvm/versions/node/v24.12.0/bin/npm
    pnpm: 10.28.0 - /Users/alexiglesiaspinol/Library/pnpm/pnpm
  Browsers:
    Chrome: 143.0.7499.193
    Firefox: 143.0.4
    Safari: 18.6
  npmPackages:
    svelte: ^5.45.6 => 5.46.1

Severity

annoyance