Add opt-in compressed class names

[nmn]

Summary

• add the enableCompressedClassnames compiler option, disabled by default
• generate short class names for common simple declarations using the property prefixes introduced in Compress common CSS property keys #1839
• cap readable class names at six characters and preserve hashing for complex, conditional, conflicting, or uncommon cases
• add Flow and TypeScript config types, validation, documentation, and end-to-end coverage

Examples

• margin: 0 → m0
• margin: 4px → m4
• paddingTop: 16px → pt16
• display: flex → d-f
• position: absolute → po-a

Stacked on #1839.

Test plan

• npm run build
• npm run docs:build
• npm run flow -- --show-all-errors
• npm run typescript
• npm run prettier:report
• npm run lint:report
• npm run test:packages

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1 Skipped Deployment

Project	Deployment	Actions	Updated
stylex	Ignored		Sep 3, 2026 8:26am UTC

[github-actions]

workflow: benchmarks/perf

Comparison of performance test results, measured in operations per second. Larger is better.
yarn workspace v1.22.22
yarn run v1.22.22
$ node ./compare.js /tmp/tmp.2G3m1yNkMi /tmp/tmp.bVNfg7VgXY

Results	Base	Patch	Ratio
babel-plugin: stylex.create
· basic create	764	770	1.01	+
· complex create	82	78	0.95	-
babel-plugin: stylex.createTheme
· basic themes	576	578	1.00	+
· complex themes	41	40	0.98	-
Done in 0.06s.
Done in 0.26s.

[github-actions]

workflow: benchmarks/size

Comparison of minified (terser) and compressed (brotli) size results, measured in bytes. Smaller is better.
yarn workspace v1.22.22
yarn run v1.22.22
$ node ./compare.js /tmp/tmp.jz06E5dWy8 /tmp/tmp.yoWZxlU9BY

Results	Base	Patch	Ratio
@stylexjs/stylex/lib/cjs/stylex.js
· compressed	1,535	1,535	1.00
· minified	5,166	5,166	1.00
@stylexjs/stylex/lib/cjs/inject.js
· compressed	1,793	1,793	1.00
· minified	4,915	4,915	1.00
benchmarks/size/.build/bundle.js
· compressed	486,580	486,580	1.00
· minified	4,076,568	4,076,568	1.00
benchmarks/size/.build/stylex.css
· compressed	99,757	99,757	1.00
· minified	748,850	748,850	1.00
Done in 0.07s.
Done in 0.31s.