Resolve volatile asset placeholders before hashing CSS in incremental builds

[astro-factory]

Changes

• Pages whose CSS references emitted assets (fonts, images via url()) now restore reliably on subsequent incremental builds instead of non-deterministically re-rendering. Vite's transform output for such CSS contains __VITE_ASSET__<handle>__ placeholders where handles are assigned per-build and are not stable across runs. The compiled CSS branch in hashModules() was passing this raw output directly to the hasher, making dependencyHash change every build even when no source file changed.
• The fix calls resolveAssetPlaceholders(graph, compiled) on the compiled CSS before hashing, replacing volatile placeholders with their stable content-hashed filenames — matching the treatment already applied to the non-CSS module code path.

Testing

• Extended packages/astro/test/units/build/plugin-incremental.test.ts to cover the CSS-with-emitted-asset case: a route importing a stylesheet that references a font above the inline threshold should produce the same dependencyHash across consecutive builds, regardless of the per-build asset handle assigned by the bundler.

Docs

• No docs update needed; this is an internal correctness fix for an existing experimental feature with no API surface change.

Closes #18058

[changeset-bot]

🦋 Changeset detected

Latest commit: c5ebeea

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

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astro	Patch

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[codspeed]

Merging this PR will not alter performance

✅ 21 untouched benchmarks

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_{Comparing factory/fix-18058 (c5ebeea) with main (cf5d72f)¹}

Footnotes

1. No successful run was found on main (db2eaf1) during the generation of this report, so cf5d72f was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[adamchal]

This fixes the CSS reference but this is still an issue with imported assets in .astro templates…