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fix(docs): drive the TOC scroll spy with an interval poll instead of events - #308
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…events The event-driven spy could not be relied on: delegated scroll listeners on document can stay silent while the container scrolls, and rAF is paused in hidden tabs, so scroll-driven activation worked only intermittently and plain-load activation raced the TOC's first render. The spy now polls the scroll container's scrollTop on a 100ms setInterval (one property read per tick, early-out when unchanged), with hashchange and a MutationObserver as immediate accelerators. A tick also re-marks when the tracked node was detached by a re-render, so activation self-heals instead of disappearing. Verified deterministic across repeated loads and scrolls: first entry active on load, last entry at the bottom, current section in between, hover on inactive entries stays at weight 400.
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Summary
Follow-up to #307. The scroll spy shipped there activates the first TOC entry on
load, but scroll-driven activation is unreliable: delegated scroll listeners on
document can stay silent while the container scrolls, and requestAnimationFrame is
paused in hidden tabs. Plain-load activation also raced the TOC's first render, so
the marker sometimes never appeared.
The spy now polls the scroll container's scrollTop on a 100ms setInterval — one
property read per tick, early-out when nothing changed — with hashchange and a
MutationObserver kept as immediate accelerators. A tick also re-marks when the
tracked node was detached by a re-render, so the active state self-heals instead
of vanishing.
Verification
Deterministic across repeated fresh loads and scrolls on a local docs build:
cargo fmt --check clean, clippy 0 warnings, full test suite passing.
Version 0.28.22, workspace pins realigned.