[fix] Fix issue with dynamic contextual styles

[nmn]

What changed / motivation ?

Just a small bug fix. Added a new test with the specific issue. Previously, the classes for contextual styles were missing spaces sometimes.

[vercel]

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Project	Deployment	Review	Updated (UTC)
stylex	Ready	Preview, Comment	Jan 27, 2026 4:50pm

[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.ltyEVjLPKW /tmp/tmp.4h8iPG61xT

Results	Base	Patch	Ratio
babel-plugin: stylex.create
· basic create	547	547	1.00
· complex create	64	68	1.06	!!
babel-plugin: stylex.createTheme
· basic themes	425	442	1.04	+
· complex themes	33	34	1.03	+
Done in 0.08s.
Done in 0.31s.

[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.V9tIKdN4Ts /tmp/tmp.sltPX3gYw4

Results	Base	Patch	Ratio
@stylexjs/stylex/lib/cjs/stylex.js
· compressed	1,311	1,311	1.00
· minified	4,150	4,150	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	496,650	496,650	1.00
· minified	4,847,840	4,847,840	1.00
benchmarks/size/.build/stylex.css
· compressed	99,853	99,853	1.00
· minified	747,541	747,541	1.00
Done in 0.08s.
Done in 0.31s.