Perf: trailing-only throttle, burst flush, O(C^2) outermost-match fix (#150 Tier 1)#151
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Tier 1 of the perf plan in #150 — plumbing wins, no architectural change. Each item targets a measured hotspot in the watcher / hide-rule loop that fires on every infinite-scroll burst and SPA route swap. lib/subtree-watcher.ts: - Trailing-only throttle. Previously `leading: true, trailing: true` ran drain at both edges of every window, so each burst scanned twice. Now coalesces to one drain at the end. - Burst-size flush. When pending grows past 512 roots (e.g. a React route swap dumping thousands of nodes in one microtask), cancel the timer and drain immediately so the user-visible hide doesn't wait out 250ms of throttle. Pattern from Ghostery's DOMMonitor. - ignoreTags filter at enqueue. Drop <style> and <br> additions before they hit the pending set — never interesting to any rule. Kept conservative: <script> stays through because json-ld-sanitize / schema-trust-sanitize observe <script type="application/ld+json"> insertions. - visibilitychange pause. Disconnect the observer when document.hidden is true (background tab), flush pending so we don't sit on a stale snapshot, reattach + drain on visible. Stops background tabs from burning CPU on observer callbacks while the user isn't looking. lib/selector-hide-rule.ts: - Memoize selectorsFor(url). Single-entry cache keyed by globalThis.location.href so the URLPattern.test loop only runs on route changes. Defensive-copy on return; internal scan() uses the cached joined selector string. - Fix O(C²) outermost-match. Replace the `candidates.some(other => other.contains(element))` filter with a Set + parentElement walk. O(C·D) instead of O(C²) — on a feed where C grows into the hundreds over a scroll session this stops being the dominant cost in scan(). Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>
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This was referenced Jun 5, 2026
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Tier 1 of #150 — plumbing wins inside
lib/subtree-watcher.tsandlib/selector-hide-rule.ts. No architectural changes; the watcher API and rule shapes are unchanged.Summary
lib/subtree-watcher.tsleading: true, trailing: true— every burst drained twice. Now coalesces to one drain at the end of the window.DOMMonitor.IGNORE_TAGSfilter at enqueue. Drop<style>and<br>additions before they hitpending. Kept conservative:<script>stays through becausejson-ld-sanitizeandschema-trust-sanitizeobserve<script type="application/ld+json">additions.visibilitychangepause. Disconnect the observer whiledocument.hidden, flush pending so we don't sit on a stale snapshot, reattach on visible. Stops background tabs from running observer callbacks.lib/selector-hide-rule.tsselectorsFor(url). Single-entry cache keyed byglobalThis.location.hrefso theURLPattern.testloop only runs on route changes. Internalscan()reuses the cached joined selector string; publicselectorsFor()returns a defensive copy.candidates.some(other => other.contains(element))with aSet<HTMLElement>+parentElementwalk. O(C·D) instead of O(C²) — matters on feeds where C grows into the hundreds over a scroll session.Tier 1 items not in this PR
Tier 1 in #150 also listed
ignoreTagsat the watcher level (done — minus<script>to stay safe) and avisibilitychangepause (done). All six Tier-1 items are landed here.Test plan
bun run test→ 1164 passed (up from 1146 — 18 new tests covering trailing-only behavior,IGNORE_TAGS, burst flush, visibility pause)bun run typecheckbun run check(biome + eslint)bun run knipbun run test:coverage— well above ratchet (statements 85.38%, branches 76.77%, functions 88.53%, lines 85.28%)Refs #150.
🤖 Generated with Claude Code