perf(weapp-tailwindcss): optimize Tailwind v4 build and HMR hot paths

[sonofmagic]

Summary

针对用户反馈的 Tailwind CSS v4 构建与 HMR 性能问题，补齐 Vite/Webpack 关键流程覆盖与阶段计时，优化已确认的候选更新和 Vite CSS 产物热点，并建立 PR 基线对比性能门禁。

Changes

• 优化 source candidate 增量更新，避免单文件变化时复制和比较完整全局候选集合
• 优化 Vite 已处理 CSS 注入后的源资产清理，只扫描 CSS 资产，并复用已解析的规则覆盖信息
• 合并 root CSS 精确去重和 scoped Tailwind 全局规则清理，减少重复 PostCSS 解析与 AST 遍历
• 保持无 root style asset 时 scoped Tailwind theme/preflight 的既有清理行为，并新增回归测试
• 为 Vite generateBundle 和 Webpack processAssets 增加阶段级 timing details
• benchmark 同时记录端到端 build/HMR 和插件处理耗时、样本数、p95 与原始 timing payload
• 新增 pnpm perf:guard：PR 对比 base SHA，push/manual 保留 current-vs-published 趋势
• 门禁阈值：插件阶段回退超过 10%；端到端回退超过 15% 且绝对增加超过 50ms
• 插件 timing 样本缺失或不完整时直接判定门禁失败
• PR 覆盖 weapp-vite、Taro Vite、Taro Webpack、uni-app Vite、Mpx 五个 Tailwind v4 场景
• PR HMR 样本由 4 轮增加到 6 轮，并使用 dev ready 后的全部真实更新样本计算中位数
• Mpx 端到端 watch 包含框架 rebuild/output flush 波动，仅作展示；processAssets 插件阶段仍执行 10% 门禁
• 新增 source candidate、processed CSS coverage、processed CSS injection 三个核心微基准和中文 Changeset

Performance

GitHub Actions 基准：29318724562，对比 PR base 2372a3649；build 3 次、HMR 6 次，表中为中位数。Performance guard 通过，0 个违规项。

Framework HMR

场景	Base	Current	变化
Taro Vite HMR	26.16s	8.96s	-65.75%
Taro Vite plugin HMR	19.46s	4.63s	-76.19%
Taro Webpack HMR	4.00s	4.18s	+4.64%
Taro Webpack plugin HMR	1.95s	1.90s	-2.81%
uni-app Vite HMR	1.33s	1.15s	-13.67%
uni-app Vite plugin HMR	685.00ms	450.50ms	-34.23%
Mpx HMR（informational）	7.01s	6.88s	-1.74%
Mpx plugin HMR	2.73s	2.63s	-3.75%
weapp-vite HMR	483.26ms	482.39ms	-0.18%
weapp-vite plugin HMR	195.00ms	183.00ms	-6.15%

Core Hot Paths

场景	Base	Current	变化
source candidate hot update	201.55ms	12.96ms	-93.57%
processed CSS coverage	200.98ms	115.56ms	-42.50%
processed CSS injection	3.87s	1.46s	-62.28%

Build 稳态中位数在五个框架上的平均变化为 -1.02%；插件 Build 平均变化为 -5.54%。

Testing

• pnpm --filter weapp-tailwindcss exec vitest run test/bundlers/vite-processed-css-assets.unit.test.ts test/ci/benchmark-report.test.ts test/ci/workflows.test.ts --pool=threads --maxWorkers=1
  • 81 tests passed
• E2E_PROJECT_FILTER='^uni-app-vite-tailwindcss-v4$' pnpm exec vitest run -c ./e2e/vitest.e2e.config.ts e2e/apps-generator-mode-compare.test.ts -t 'builds retained demos'
  • uni-app generator 小程序、H5、App 输出快照通过，未更新基线
• pnpm --filter weapp-tailwindcss build
• benchmark production scripts ESLint and node --check
• CI 29318724517 passed，包括 Quality、Compatibility、E2E Static、Focused、Multiplatform 与 Watch gates
• Release Gate 29318724518 passed
• Benchmark 29318724562 passed，五框架与三个 core 场景均无错误且 timing 样本完整

pnpm --filter weapp-tailwindcss test completed with 2815 passed and 10 snapshot indentation failures. These failures reproduce in the origin/main baseline; no unrelated snapshots were updated.

[changeset-bot]

🦋 Changeset detected

Latest commit: b2f728f

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
weapp-tailwindcss	Patch
@weapp-tailwindcss/build-all	Patch
@weapp-tailwindcss/website	Patch

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