polish: localStorage safety, scroll perf, a11y, dead code, modernize CSS

[Arty2]

Why

A read-only audit of the codebase outside the recent forge-meta-security (#2), css-modernize (#3), and modifier-docs (#4) PRs surfaced a cluster of small, isolated wins that share one theme: stop relying on patterns that no longer pull their weight. Three Explore agents proposed 30+ items; manual cross-checking eliminated the false positives (one agent flagged the taxon partial as orphaned despite live usage at tags-list.html:3 + articles-filter.html:15; another flagged the just-documented .no-* modifiers as orphans). What landed below is verified line-by-line.

What

Robustness — localStorage try/catch

localStorage.getItem and setItem are wrapped in try / catch. Safari Private Mode throws QuotaExceededError (and on older Safari, even on read), which today crashes both the inline theme bootstrap and the toggle handler.

• layouts/_default/baseof.html:9-24 — bootstrap rewritten; theme is now declared with let instead of being an implicit global created by if (theme = localStorage.getItem('theme')).
• static/scripts/onion.js:124 — setItem wrapped; in-memory toggle still works in Private Mode, just no persistence.

Scroll perf — setInterval(1000) → passive scroll listener

onion.js:67–81 polled window.scrollY every second to swap the #scroller gadget between up/down/hidden. Replaced with window.addEventListener('scroll', update, { passive: true }) plus an initial update() call. Same logic, instant response (was up to 1 s lag), zero idle-time work.

Accessibility

• aria-current="page" on active main-nav links — top-level and nested children. Mirrors the existing idiom at languages.html:5.
• aria-label on the icon-only #themer and #scroller <a> elements in gadgets.html. New i18n keys toggle-theme and scroll-top in both en.yaml and el.yaml.
• Search form wrapped in <search> landmark (HTML Living Standard, Safari 17 / Chrome 120 / Firefox 118; older browsers degrade to a generic block element with no behavioural impact).

Per-page menu cache fix

header-inner.html:11 called partialCached "menu-main" . with no variant key, so Hugo cached the first render and reused it for every page — meaning aria-current would have been pinned to whichever page Hugo rendered first. Added .RelPermalink as the variant key.

JS modernization — var → const / let

All ~15 sites in static/scripts/onion.js. const for never-reassigned (lbBase, lbCss, galleries, figures, slideAnimation); let for loop counters (index_current, index, z). The themer and scroller IIFEs were also restructured around early-return guards. The themer.onclick handler used an undeclared event reference (worked in Chromium via window.event, broken in Firefox) — handler now takes event as a parameter.

CSS modernization

Removed / changed	Why
3× -webkit-transition paired with unprefixed siblings	Safari has supported unprefixed transition since 9 (2015)
2× -webkit-mask-image → mask-image	Safari 15.3+ (2022) supports unprefixed
-webkit-appearance: button	iOS Safari 15+ has native parity
2× commented-out -webkit-mask-image	dead

Dead code

• --theme--toggle: 0 (double dash, typo) declared in .theme--gray and .theme--blue — never read. Deleted from both.
• i18n key description ("Summary") — defined in en.yaml and el.yaml but no template references. Deleted from both. Note: rss-about was also flagged by the audit but IS used at layouts/_default/index.xsl:41 — kept.
• Three stale TODO comments resolved/removed (screen.css:866, screen.css:1567, articles-filter.html:26).

Test plan

• cd exampleSite && hugo --gc --minify — clean, no warnings
• npx html-validate@^9 --config .github/html-validate.json public/**/*.html — exit 0
• grep -rnE "theme--toggle|-webkit-(transition|appearance|mask-image)" assets/styles/screen.css — empty
• grep -c "^\s*var " static/scripts/onion.js — 0
• Rendered HTML spot-check: aria-current=page on /archives/ only (not on /); gadget icons emit aria-label="Toggle theme" / "Scroll to top"
• Manual: theme toggle round-trips correctly (click → reload → persists); DevTools "block localStorage" → toggle still works in-memory, no console error
• Manual: scroll a long page — gadget arrow swaps up↔down instantly (was up to 1 s lag before)
• Manual: VoiceOver / NVDA reads "current page" on the active main-nav item; both gadget icons announce their purpose

Out of scope (next branch, stacked)

claude/print-stylesheet will add a separate assets/styles/print.css linked with media="print". Reading-time, OG image dimensions, dark-mode favicon, and apple-touch-icon were considered and dropped per maintainer call ("very little benefit").

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