Fix Vite issues with SolidStart

[philipp-spiess]

Fixes #16045

This PR fixes two Vite issues found with SolidStart:

• SolidStart seems to emit an empty HTML chunk (where the content is literally just /) with no pathname. Since we use the path to generate an id for HTML chunks, this would currently cause a crash. This was reported in @tailwindcss/vite v4.0.1 not working Cannot read properties of undefined (reading 'includes') #16045
• While testing the fix for the above, we also found that hot reloading was not working in SolidStart since 4.0.0-alpha.22. After doing some bisecting we found that this is happening as SolidStart has the same module ID in different servers and we were invalidating the root when we shouldn't. After trying to restructure this code so that it only cleans up the root when it is no longer part of any server, we noticed some other compatibility issues with Nuxt and SvelteKit. It seems that the safest bet is to no longer update a root at all during rebuilds in the SSR step. This makes invalidateAllRoots a function that only notifiers the servers about a change which is conceptually also less confusing.

Test plan

• Added an integration test for SolidStart dev mode
• Manually tested the dev mode across all Vite based templates in https://github.com/philipp-spiess/tailwindcss-playgrounds: Astro, Nuxt, Remix, Solid, SvelteKit, and Vue.

[RobinMalfait]

Now that we don't remove any roots anymore, I'm not sure how this will behave over a longer time (memory wise). But the only real issue would be if you create a lot of new CSS files I think anyway so should be fine?

Left a few comments

[RobinMalfait]

😍

[RobinMalfait]

I'm not 100% sure why this is safe to do this unconditionally. Is it just because we are never removing any roots anymore?

[philipp-spiess]

We're no longer calling roots.delete(id) so this check can be removed too, not sure I understand your question correctly tho? 😅

[RobinMalfait]

I'm being a dumb dumb, carry on.

[philipp-spiess]

Now that we don't remove any roots anymore, I'm not sure how this will behave over a longer time (memory wise). But the only real issue would be if you create a lot of new CSS files I think anyway so should be fine?

Yeah I think ultimately this is going to need some sort of LRU cache and some extra bookkeeping but it does seem like it's not safe way to assume a module has been downloaded by trying to look at which servers still have the module loaded :/