[tmashara]

Refs #150

A Stylelint autofix that turns -webkit-text-size-adjust, -webkit-background-clip: text and -webkit-user-select into their unprefixed forms passes a Chromium run on pixels and on --computed. Chromium honours both spellings, and its CSSOM serialises the prefixed name as the unprefixed one, so even rule coverage sees identical rules. Shooting in WebKit doesn't help either: measured on Playwright WebKit 26.5, none of the three changes a pixel, and desktop WebKit drops both spellings of text-size-adjust when it parses them.

So --computed now also reads each side's CSS as written and compares the vendor-prefixed declarations.

• Source: every main-frame stylesheet response body, read in page.on("response") while it is still available, which covers cross-origin sheets the CSSOM can't read. Also the text of every <style>, open shadow roots included.
• Comparison: a multiset of -(webkit|moz|ms|o)-prop: value declarations, with comments and whitespace normalised, ignoring which selector or file holds them. Minifying, reordering, moving a declaration between files or a new asset hash is no finding; one side holding an extra copy is.
• Output: a prefixes: block after rules:, informational like it, never changing the exit code. Up to 10 declarations shown per side with (+N more).
• results.json: computed.prefixes: { left, right } per shot and summary.prefixes ({ side, declaration, at }).

prefixes: 3 prefixed declarations only one side has
  only left has: -webkit-background-clip: text; -webkit-text-size-adjust: 100%; -webkit-user-select: none  /prefix@1440,375

Not seen: insertRule, adopted sheets, style attributes, and prefixed selectors, media features or values. The docs say so.

Tests

• Unit: extraction, covering normalisation, what it leaves out (selectors, media features, values) and the multiset diff; and the console block, covering the cap and the empty line.
• prefix fixture: one prefixed declaration in an inline <style>, one in a same-origin <link>, one in a cross-origin <link> (localhost vs 127.0.0.1, unreadable to the CSSOM). Chromium keeps pixel parity and lists all three.
• prefix-same fixture: the same set minified, reordered, moved between <style> and sheet, under a hashed file name. No finding.
• The equivalence and control corpus under --computed: no prefix findings. Run by hand over the whole corpus (60 routes × 2 widths): none either.
• typecheck, lint, format:check, npm test, and the guardrails, computed, controls, equivalence and accepted visual files pass locally.

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