Disable legacy mode in the tutorial

[sacrosanctic]

New users are confused that their state is still reactive without $state.

• https://www.reddit.com/r/sveltejs/comments/1jk33dd/svelte_5_state_tutorial/
• Svelte Tutorial Universal State updating without $state #1229
• https://discord.com/channels/457912077277855764/1358713915084771335
• https://discord.com/channels/457912077277855764/1358786304476840108

[seantiz]

Another case in point https://discord.com/channels/457912077277855764/1358494780673359882

[brunnerh]

I do not think we need this as a separate issue. Suggestions can be left at the existing one.
(We also do not really need any more "evidence", the same thing has been reported multiple times by now.)

[sacrosanctic]

@brunnerh I’d say this is more of a feature request, while that’s a bug report. But I get the need to keep things consolidated. Can you rename #1229 to reflect the broader scope?

[brunnerh]

I would prefer to keep it a plain bug report and leave it to the maintainers to decide what to do with it.

Disabling legacy mode would be one way of dealing with it, but it has its own downsides. As long as legacy mode exists, it can have unexpected side effects when it activates by accident, so hiding it entirely may not be the best approach. I guess it would be fine if legacy mode (and its absence from the tutorial) is at least explained early on.

[sacrosanctic]

I think we can find a compromise by explicitly declaring rune mode as shown here.

https://www.sveltepatterns.dev/how-to-force-rune-mode#per-component

And we only need to add this on specific tutorials where this is likely to happen. I think there's only 1.