fix: align eager, lazy, and LCP image hints with HTML standard

[seonghobae]

What

• 첫 화면의 eager 이미지와 유일한 fetchpriority="high" LCP 후보에서 강제 decoding="async"를 제거해 사용자 에이전트의 표준 기본값 auto에 맡깁니다.
• 명시적인 loading="lazy" 이미지에는 decoding="async"를 유지합니다.
• eager, lazy, LCP 집합의 존재와 힌트 조합을 각각 검증하여 vacuous pass를 차단합니다.
• HTML Living Standard와 Fetch Priority 공식 문서를 APA 7th 형식으로 성능 doctoring 문서에 기록합니다.

Why

decoding은 이미지 표시 방식에 관한 선호 힌트이고, 속성이 없으면 auto입니다. fetchpriority는 별도의 fetch 우선순위 힌트입니다. 따라서 SVG에 디코딩이 없다고 가정하거나 속성 제거만으로 LCP 개선을 단정하지 않고, 중요한 이미지는 브라우저 판단에 맡기며 fetch 우선순위 계약을 독립적으로 검증합니다.

Verification

• python3 -m pytest tests/
• exact current head의 보안·정적 분석·리뷰·필수 checks
• 배포 후 LCP 실측은 별도 관측 대상으로 유지

References

• WHATWG. (2026, July 20). HTML standard: The img element.
• Osmani, A., Sohoni, L., Meenan, P., & Pollard, B. (2023, November 14). Optimize resource loading with the Fetch Priority API. web.dev.

이 PR은 동일 목적의 #81, #89, #92, #95, #98을 통합하는 canonical PR입니다.

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[Copilot]

Pull request overview

This PR optimizes LCP for the static homepage by removing decoding="async" from above-the-fold SVG images (logo + hero), and updates the regression test to apply the async-decoding rule only to lazy-loaded images.

Changes:

• Remove decoding="async" from the header logo SVG and hero SVG to avoid delaying LCP rendering.
• Update tests/test_styles.py to validate decoding="async" only for loading="lazy" images.
• Document the change in CHANGELOG.md and record the performance learning in .jules/bolt.md.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
index.html	Removes async decoding on LCP/above-the-fold SVGs while keeping async decoding on lazy-loaded images.
tests/test_styles.py	Narrows the async-decoding assertion to lazy-loaded images.
CHANGELOG.md	Adds an Unreleased entry for the LCP optimization.
.jules/bolt.md	Adds a performance journal entry capturing the new rule of thumb for LCP images.

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📥 Commits

Reviewing files that changed from the base of the PR and between d06c1cb and fa518c4.

📒 Files selected for processing (4)

• .jules/bolt.md
• CHANGELOG.md
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[seonghobae]

Closing as superseded by #141. The current-base PR now carries forward this PR's valid standards reasoning, non-vacuous eager/lazy/LCP image contracts, bounded performance claims, and APA 7th doctoring references without the stale-base and unrelated-history conflicts present here. No unique required change remains in this branch.

[google-labs-jules]

Closing as superseded by #141. The current-base PR now carries forward this PR's valid standards reasoning, non-vacuous eager/lazy/LCP image contracts, bounded performance claims, and APA 7th doctoring references without the stale-base and unrelated-history conflicts present here. No unique required change remains in this branch.

Understood. Acknowledging that this work is now obsolete and stopping work on this task.