feat: capture normalized computed style from rendered elements

[hungify]

Summary

• Add captureElementStyle(page, selector) to packages/playwright/src/capture-style.ts, reading an element's live computed style via getComputedStyle (through Playwright's page.$eval) and normalizing it into a StyleSnapshot.
• Normalization: color (rgb()/rgba()) → lowercase hex, dropping alpha; paddingTop/Right/Bottom/Left → numeric spacing box; fontSize → number; fontWeight → numeric, mapping browser-inconsistent keyword forms ("normal"/"bold") to their numeric equivalents; borderRadius corners → single cornerRadius number only when all four corners agree, otherwise left undefined.
• Matches the StyleSnapshot shape ticket Figma-side style extraction (StyleSnapshot) #5 owns on the Figma side, so the two snapshots are directly comparable. Figma-side style extraction (StyleSnapshot) #5 hadn't landed a @framelia/verify export at the time of this PR, so StyleSnapshot is defined locally in capture-style.ts with a TODO(#5/#6 merge) comment — dedupe against @framelia/verify's export once both land.
• Takes page as a dependency rather than constructing its own browser/page, matching the existing pattern in capture.ts.
• Not wired into the compare pipeline or to-match-figma.ts matcher (ticket Per-contract threshold override #7, out of scope here). Does not touch packages/verify (ticket Figma-side style extraction (StyleSnapshot) #5's territory).

Test plan

• TDD, one seam at a time, against a real Playwright Page via page.setContent (no mocking getComputedStyle):
  • rgb() color → lowercase hex
  • rgba() color → lowercase hex, alpha dropped
  • padding → numeric spacing box
  • fontSize → number
  • fontWeight numeric string → number
  • fontWeight keyword (bold) → numeric equivalent (700)
  • equal border-radius corners → single cornerRadius
  • unequal border-radius corners → cornerRadius left undefined
• Full packages/playwright suite green (26/26), typecheck clean

Closes #6

Summary by CodeRabbit

• New Features

  • Added a utility to capture an element’s computed visual styles, including colors, spacing, typography, and corner radius.
  • Normalizes captured values into consistent formats for easier inspection and comparison.
  • Reports a corner radius only when all corners use the same value.

• Tests

  • Added coverage for color, spacing, font, font-weight, and corner-radius handling.

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Review details

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 02df1037-9e60-4b92-9bfc-12738cf17d67

📥 Commits

Reviewing files that changed from the base of the PR and between 6004bb6 and 13c0485.

📒 Files selected for processing (2)

• packages/playwright/src/capture-style.ts
• packages/playwright/tests/capture-style.test.ts

📝 Walkthrough

Walkthrough

Adds StyleSnapshot and captureElementStyle to capture normalized computed styles from a selected element. The implementation normalizes colors, spacing, font values, and uniform corner radii. Tests cover browser lifecycle and normalization behavior.

Changes

Computed style capture

Layer / File(s)	Summary
Style contract and normalization packages/playwright/src/capture-style.ts	Defines StyleSnapshot and normalizes pixel values, font weights, RGB/RGBA colors, and uniform corner radii.
Page capture and validation packages/playwright/src/capture-style.ts, packages/playwright/tests/capture-style.test.ts	captureElementStyle reads computed styles through the supplied Playwright page. Tests verify color, spacing, typography, and corner-radius output.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: 🔵 Low · up to 6004b

The helper may misrepresent elements using elliptical border radii by returning only one axis, which could produce inaccurate style comparisons once integrated. This is a localized, bounded correctness risk and is mergeable with explicit owner follow-up; adding the requested normalization fix and regression test is recommended.

Sequence Diagram(s)

sequenceDiagram
  participant captureElementStyle
  participant PlaywrightPage
  participant SelectedElement
  captureElementStyle->>PlaywrightPage: query selector
  PlaywrightPage->>SelectedElement: read computed styles
  SelectedElement-->>PlaywrightPage: return raw style values
  PlaywrightPage-->>captureElementStyle: return style properties
  captureElementStyle-->>captureElementStyle: normalize into StyleSnapshot

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🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the main change: capturing normalized computed styles from rendered elements.
Linked Issues check	✅ Passed	The implementation meets issue #6 by normalizing styles, including colors and font weights, and accepting an existing Page.
Out of Scope Changes check	✅ Passed	The source and test changes directly support computed-style capture and its required normalization behavior.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch worktree-issue-6-capture-style

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Actionable comments posted: 2

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Inline comments:
In `@packages/playwright/src/capture-style.ts`:
- Around line 44-53: Update normalizeCornerRadius to preserve both axes when
parsing each corner radius: return a scalar only when every corner is compatible
and its horizontal and vertical pixel values are equal; otherwise return
undefined. Add a regression test covering border-radius: 12px / 8px and verify
it does not produce a scalar radius.

In `@packages/playwright/tests/capture-style.test.ts`:
- Around line 63-69: Update the font-weight normalization test around
captureElementStyle to directly exercise the FONT_WEIGHT_KEYWORDS branch by
supplying raw “normal” and “bold” values, rather than relying on Chromium’s
computed-style serialization. Assert that these keywords normalize to their
expected numeric equivalents.

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• Create a new PR with the fixes

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ℹ️ Review info

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Configuration used: defaults

Review profile: CHILL

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📥 Commits

Reviewing files that changed from the base of the PR and between 507510e and 6004bb6.

📒 Files selected for processing (2)

• packages/playwright/src/capture-style.ts
• packages/playwright/tests/capture-style.test.ts

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[hungify]

Around line 44-53: Update normalizeCornerRadius to preserve both axes when parsing each corner radius: return a scalar only when every corner is compatible and its horizontal and vertical pixel values are equal; otherwise return undefined. Add a regression test covering border-radius: 12px / 8px...

Not addressing: already handled as of this branch's HEAD (capture-style.ts:45-67) — parseCornerRadius parses both axes and normalizeCornerRadius only collapses to a scalar when every corner is circular (horizontal === vertical) and all four agree. The regression test for border-radius: 12px / 8px already exists at capture-style.test.ts:99-106. This review comment was posted against an earlier commit in the range before that fix landed.