Don't trigger a full page reload for scanned files that Vite processes as modules

[RobinMalfait]

This PR fixes an issue where editing a scanned file that Vite (or one of its plugins) can process as a module, but that isn't currently loaded, caused @tailwindcss/vite to force a full page reload, throwing away all client state.

The hotUpdate hook has a fallback that sends a full-reload for files that Tailwind scans but that Vite knows nothing about (e.g. .php or .blade.php templates rendered by a backend). Without it, edits to those files wouldn't refresh the page at all. To detect those files we check whether every module for the changed file is an asset and/or has no id, because the scanner's addWatchFile calls create exactly such placeholder nodes for every scanned file.

The problem is that a source file that Vite can process, but that isn't loaded yet, looks exactly the same. The realistic way to get into that state is code splitting: with route-level splitting (e.g. React.lazy, TanStack Router's autoCodeSplitting, lazy routes in vue-router), every component behind an un-visited split boundary only exists as a scan placeholder in the module graph. Editing any of them reloaded the whole app. The same happens for component stylesheets that a framework plugin compiles into the component (e.g. Angular via Analog), which never show up as their own module.

A full reload is never useful for these files: if the file is loaded, Vite's own HMR handles it, and if it isn't loaded, reloading the page won't load it either. Any new candidates still apply through the regular css-update flow because the file is registered via addWatchFile.

So instead, we now skip the fallback when the changed file is handled by Vite's module pipeline:

• The file exists as a real module in another environment (e.g. an SSR-only module). This check already existed and is folded into the same code path.
• The file is part of the JS/TS or CSS families, which Vite transforms natively.
• For any other file type (e.g. .vue, .svelte, or .md with an SSG plugin), a file with the same extension exists as a real module in some environment's module graph, then a plugin does handle this file type and the changed file just isn't loaded (yet).

External templates like .php files still trigger a full reload exactly like before.

Fixes: #20320
Fixes: #19903
Closes: #20323

Test plan

1. Added integration tests to ensure extensions handled by default rely on HMR
2. Added integration tests to make sure that unknown extensions that have been handled already will also use HMR
3. Manually tested that changing a .php file still triggers a full-reload
4. Manually tested the reproduction where local client state isn't thrown away

[greptile-apps]

Confidence Score: 5/5

The change is safe to merge. It only makes the hotUpdate hook return early in cases where a full reload was never useful, and the PHP/external-template path remains unchanged and is directly tested.

The heuristics are well-layered: hardcoded families (JS/TS, CSS) are checked cheaply before the module graph scan, the scan itself is bounded to one pass per new extension type via the viteProcessedExtensions cache, and the edge cases most likely to produce false positives (?raw query imports, asset-only modules, SSR-only modules) are each explicitly handled. Integration tests cover all four distinct file categories, and the full-reload assertion for PHP templates runs after the non-reload assertions so they remain independent.

No files require special attention. The implementation in packages/@tailwindcss-vite/src/index.ts is the only non-test change and is straightforward.

_{Reviews (1): Last reviewed commit: "update changelog" | Re-trigger Greptile}

[coderabbitai]

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• CHANGELOG.md

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Walkthrough

The Vite plugin now detects files transformed as modules across Vite environments and caches confirmed extensions before deciding whether external changes require a full reload. New integration tests cover unloaded .tsx, custom, stylesheet, and Vue files, while preserving full reload behavior for external PHP templates. The tests also record HMR payloads and verify generated CSS updates.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main behavior change: skipping full reloads for scanned files Vite can process as modules.
Description check	✅ Passed	The description matches the code changes and explains the bug, fix, and tests.
Linked Issues check	✅ Passed	The changes address #20320, #19903, and #20323 by avoiding reloads for handled scanned files while preserving reloads for external templates.
Out of Scope Changes check	✅ Passed	The added tests and hotUpdate logic stay focused on the reload-fallback fix with no unrelated feature work.

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