Build: Update Vite to 8.3.2 and remove the PostCSS browser resolver

[ciampo]

Follow-up to #83091 and #83635.

What?

Update Vite to 8.3.2 and remove the temporary PostCSS browser resolver from Browser Mode and Storybook.

Why?

Vite 8.3.2 includes the upstream fix for browser-externalized warnings when PostCSS probes imports mapped to false in its browser configuration.

How?

Update the three Vite development dependencies and the shared lockfile resolution. Delete the resolver and both registrations. Retain the Browser Mode regression for CSS transformation and asset URL rebasing, and the Storybook static smoke checks.

Testing Instructions

1. Run npm ci and npm run build.
2. Run npm run test:unit:vitest:shuffled -- --sequence.seed=20261001 --project=browser. The retained PostCSS regression must pass, including selector scoping and asset URL rebasing, without browser-externalized warnings.
3. Run NODE_ENV=test npm run storybook:build, then npm run --workspace @wordpress/storybook test:smoke. All built stories should render with successful asset requests, and the Chromium story tests should pass without browser-externalized warnings.

Local verification

• The retained regression failed on Vite 8.3.1 with the resolver removed, then passed on 8.3.2.
• Browser Mode passed all 126 files with seed 20261001: 1,691 tests passed and 72 expected failures.
• All 891 static Storybook stories rendered successfully.
• Storybook Chromium passed all 233 files and 891 tests, without browser-externalized warnings.
• The theme build-plugin integration tests passed all 32 tests.
• Production build, both Storybook builds, typecheck, focused JavaScript and package JSON lint, dependency consistency, lockfile, peer dependency, and published dependency checks passed. The regenerated Storybook manifest was unchanged.
• The separate PostCSS missing-from warning still appears in Browser Mode. It was already documented alongside the resolver and remains outside this browser-externalized warning fix.
• The theme changelog passes validation and cites this PR. Repository-wide changelog validation finds an existing duplicate Bug Fixes section in the unchanged DataViews changelog.
• npm audit reports the same 53 existing advisories before and after the update, with none for Vite or Rolldown.

Use of AI Tools

Codex implemented the dependency and configuration changes, ran local verification, and drafted this description.

[github-actions]

🤖 PR meta 🤖

🎉 Props

If you're merging code through a pull request on GitHub, copy and paste the following into the bottom of the merge commit message.

Co-authored-by: ciampo <mciampini@git.wordpress.org>
Co-authored-by: Mamaduka <mamaduka@git.wordpress.org>

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

Updated as activity occurs, without notifying anyone named here. Add the props-bot label to refresh.

📦 Bundle size

Size Change: 0 B

Total Size: 8.25 MB

_{bf8d43c Run}

⚡ Performance

Show the results

Client side metrics exclude the server response time.

front-end-block-theme

Metric	8f8f41f	trunk	% Change
timeToFirstByte	56.75 ms +5.81% -1.67%	65.2 ms +7.52% -9.89%	-12.96%
largestContentfulPaint	94 ms +12.77% -2.13%	104 ms +3.85% -7.69%	-9.62%
lcpMinusTtfb	36.9 ms +23.17% -3.39%	37.3 ms +2.82% -4.29%	-1.07%
wpBeforeTemplate	27.69 ms +2.71% -0.4%	30.35 ms +20.63% -5.6%	-8.76%
wpTemplate	24.66 ms +4.34% -3.57%	27.86 ms +7.18% -6.32%	-11.49%
wpTotal	52.68 ms +5.77% -1.63%	60.74 ms +7.8% -9.94%	-13.27%
wpMemoryUsage	7.62 MB +0% -0%	7.59 MB +0% -0%	0.46%
wpDbQueries	17 +0% -0%	17 +0% -0%	0%

front-end-classic-theme

Metric	8f8f41f	trunk	% Change
timeToFirstByte	46.2 ms +5.41% -1.95%	51.5 ms +3.98% -5.53%	-10.29%
largestContentfulPaint	104 ms +0% -3.85%	108 ms +1.85% -1.85%	-3.7%
lcpMinusTtfb	56.25 ms +3.11% -2.58%	57.4 ms +1.57% -2.26%	-2%
wpBeforeTemplate	24.49 ms +3.67% -1.22%	26 ms +14.04% -3.88%	-5.81%
wpTemplate	18.32 ms +1.31% -2.29%	20.36 ms +10.85% -5.7%	-10.02%
wpTotal	42.68 ms +6.21% -1.24%	48.02 ms +3.81% -6.08%	-11.12%
wpMemoryUsage	6.25 MB +0% -0%	6.20 MB +0% -0%	0.71%
wpDbQueries	14 +0% -0%	14 +0% -0%	0%

media-processing

Metric	8f8f41f	trunk	% Change
mediaProcessingJpeg	414.42 ms +5.1% -0.51%	418.05 ms +1.37% -0.55%	-0.87%
mediaProcessingAvif	6170.66 ms +0.34% -0.07%	6148.37 ms +0.21% -0.21%	0.36%
mediaProcessingJpegToAvif	4316.24 ms +0.14% -0.17%	4297.93 ms +0.48% -0.08%	0.43%

media-upload

Metric	8f8f41f	trunk	% Change
jpegUploadProcessing	1710.01 ms +15.69% -15.83%	1442.09 ms +1.04% -1.05%	18.58%
pngUploadProcessing	193.65 ms +22.63% -11.03%	215.67 ms +5.45% -15.63%	-10.21%
largeJpegUploadProcessing	1423.92 ms +0.86% -0.4%	1422.25 ms +1.36% -0.9%	0.12%
multipleImageUploadProcessing	2079.46 ms +2.6% -1.85%	1608.69 ms +26.49% -0.35%	29.26%

post-editor

Metric	8f8f41f	trunk	% Change
serverResponse	508.11 ms +3.64% -11.15%	507.57 ms +2.4% -3.1%	0.11%
firstPaint	218.97 ms +10.03% -20.26%	223.55 ms +21.44% -11.67%	-2.05%
domContentLoaded	1102.45 ms +0.39% -2.21%	1085.17 ms +1.54% -1.86%	1.59%
loaded	1103.62 ms +0.39% -2.18%	1086.45 ms +1.51% -1.86%	1.58%
firstContentfulPaint	450.52 ms +3.65% -0.97%	443.38 ms +2.26% -3.87%	1.61%
firstBlock	3251.97 ms +0.55% -1.55%	3238.41 ms +0.49% -2.24%	0.42%
type	18.3 ms +4.37% -5.74%	17.23 ms +1.28% -1.45%	6.21%
typeWithoutInspector	17.09 ms +1.4% -7.43%	16.38 ms +4.7% -4.95%	4.33%
typeWithTopToolbar	21.13 ms +3.45% -1.37%	21.42 ms +2.89% -3.92%	-1.35%
typeContainer	8 ms +3.13% -5.87%	8.47 ms +6.38% -6.73%	-5.55%
focus	72.92 ms +15.88% -13.38%	68.09 ms +9.77% -4.46%	7.09%
firstFocus	195.54 ms +0% -0%	193.58 ms +0% -0%	1.01%
selectAll	507.17 ms +9.25% -0.32%	533.05 ms +0.41% -0.15%	-4.86%
listViewOpen	62.17 ms +1.01% -18.47%	63.37 ms +8.27% -6.74%	-1.89%
inserterOpen	21.45 ms +4.34% -9.88%	22.04 ms +14.7% -16.52%	-2.68%
inserterHover	2.15 ms +6.98% -7.91%	2.14 ms +13.08% -11.21%	0.47%
inserterSearch	7.65 ms +10.72% -4.97%	7.82 ms +7.03% -4.35%	-2.17%
loadPatterns	594.96 ms +5.2% -1.61%	605.34 ms +4.39% -1.68%	-1.71%
wpTotal	497.86 ms +3.42% -11.36%	497.67 ms +2.38% -3.25%	0.04%
wpMemoryUsage	13.17 MB +0% -0%	13.13 MB +0% -0%	0.28%
wpDbQueries	54 +0% -0%	54 +0% -1.85%	0%

site-editor

Metric	8f8f41f	trunk	% Change
serverResponse	410.29 ms +2.27% -5.95%	386.1 ms +6.44% -5.33%	6.27%
firstPaint	224.27 ms +18.14% -8.45%	231.72 ms +16.68% -8.2%	-3.22%
domContentLoaded	1149.18 ms +1.02% -1.21%	1123.57 ms +0.97% -0.7%	2.28%
loaded	1150.45 ms +1.02% -1.19%	1124.75 ms +0.97% -0.7%	2.28%
firstContentfulPaint	454.24 ms +4.26% -2.29%	462.7 ms +1.58% -3.75%	-1.83%
firstBlock	4026.62 ms +1.38% -0.43%	3957.54 ms +0.21% -0.98%	1.75%
type	18.88 ms +1.75% -6.67%	18.46 ms +5.15% -7.2%	2.28%
navigate	123.01 ms +6.11% -6.67%	115.41 ms +17.91% -3.8%	6.59%
loadPatterns	1336.2 ms +6.22% -12.18%	1219.36 ms +10.54% -3.77%	9.58%
loadPages	1102.84 ms +0.9% -1.35%	1082.09 ms +1.81% -0.54%	1.92%
wpTotal	399.19 ms +2.38% -6.01%	375.25 ms +6.53% -5.5%	6.38%
wpMemoryUsage	12.14 MB +0% -0%	12.10 MB +0% -0%	0.4%
wpDbQueries	43 +2.33% -0%	43.5 +1.15% -1.15%	-1.15%

_{bf8d43c Run}

[Mamaduka]

That was fast 🚀