fix(accessibility): reconcile robust focus appearance after #270

[seonghobae]

Objective

Reconstruct the bounded WCAG focus-appearance fix directly on the protected-main baseline after #270 integrated, so base-sensitive verification runs without predecessor ancestry.

Fresh exact state — 2026-08-10

• exact source head: d080540076703d2e94940522f18ac6be86d2da37;
• exact protected main: 55d7ae8647208e301f282350f076eeddaba61d11;
• clean delta: two changed files, merge base exactly protected main;
• the final commit is an intentional same-tree verification trigger because the prior clean source head had no Actions runs attached; it changes no file content;
• exact-head CI 31389256791: success;
• exact-head Security Scan 31389256767: success;
• exact-head SAST Semgrep 31389256739: success;
• exact-head fuzz 31389256710: success;
• no automated check, comment, status, or model output is qualifying independent approval.

Preserved accessibility contract

The shipped :focus-visible rule uses:

• a 3px black outline with a 3px offset;
• a 3px white box-shadow band;
• no pointer-only focus replacement and no added animation.

The deterministic contract computes WCAG relative luminance and contrast, requiring at least 2 CSS px at >=3:1 against both white and black reference surfaces. It also prevents overlapping outline/shadow pixels from being double-counted by limiting the exposed shadow band to the outline offset.

Exact source identity

Changed blobs:

• scripts/test_viewer_focus_appearance.py: ad1509e12b147582f6e3e824b9ff00fb34921b8e;
• src/main/resources/static/assets/viewer/viewer.css: 3c19c3baccaaffdf1aa5277187591703aa8deb07.

The protected-main CSS before reconstruction was byte-identical to the former #325 base, proving #270 did not modify this path. #325 remains predecessor evidence only and is superseded by this current-base branch.

Scope / non-completion boundary

This two-file slice does not modify viewer generation ownership (#322/#323), demo/session authority (#317), nested asynchronous controls (#264), Java controllers, build metadata, or canonical cross-cutting documentation. Issue #324 remains the product and standards authority.

Merge gate

Keep this exact head unchanged. Auto-merge may complete only after live repository protection still sees all required checks passing, zero valid unresolved findings, and the counted approving review from a qualifying independent reviewer with write access. Automated evidence is not approval.

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Review details

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: fa91ae1b-44f4-4e36-8aab-371978e76767

📥 Commits

Reviewing files that changed from the base of the PR and between b66b692 and 00f79a3.

📒 Files selected for processing (2)

• scripts/test_viewer_focus_appearance.py
• src/main/resources/static/assets/viewer/viewer.css

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[seonghobae]

@opencode-agent @cwl-noema-review Please independently review exact current head d080540076703d2e94940522f18ac6be86d2da37 against protected main 55d7ae8647208e301f282350f076eeddaba61d11. Exact-head CI 31389256791, Security Scan 31389256767, SAST 31389256739, and fuzz 31389256710 are successful. Verify the two-tone focus contract provides at least 2 CSS px at >=3:1 on both light and dark surfaces, preserves :focus-visible, does not double-count overlapping shadow pixels, and remains path-disjoint from viewer-generation, demo/session, and nested async-control work. The final commit is same-tree verification only. Advisory review; do not mutate, count as human approval, merge, or weaken gates.