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PERFORMANCE-AUDIT.md

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Performance Audit

Scope

Post-release runtime audit for the userscript with a behavior-parity constraint:

  • no architecture redesign
  • no public API or config-schema changes
  • focus on long-session stability, observer/listener hygiene, DOM churn, and async cleanup

Findings

  1. Several features were waking twice for the same state change. Direct gameState.subscribe() callbacks and eventBus.on("game-state:updated") subscriptions were both scheduling the same feature work.

  2. Multiple features were observing DOM subtrees they also mutated. Overlay insertion, transient FX nodes, animated text updates, and shell-managed DOM changes could reschedule their own features even when nothing external changed.

  3. Some high-cost DOM discovery was repeated on unchanged DOM. Board and cricket-grid discovery scanned the full document on every scheduled update, even when only game state changed.

  4. A small set of async paths could outlive feature teardown. Lazy vendor loading for winner-fireworks and turn-points-count could schedule late work after cleanup if not explicitly guarded.

  5. Optional polling paths could still wake hidden tabs. This was low-frequency, but it was still unnecessary long-session work.

Changes Applied

Runtime and State Flow

  • Removed redundant feature-side eventBus.on("game-state:updated") subscriptions.
  • Standardized feature updates on direct gameState.subscribe() only.
  • Added lightweight duplicate websocket-state suppression in src/core/game-state-store.js for identical consecutive payloads.

Mutation Observers

  • Added src/core/dom-mutation-filter.js as the shared helper for managed-node mutation filtering.
  • Reused that helper in shell and feature observers where the feature owns inserted overlays or transient nodes.
  • Tightened observer scopes so text-only decorators no longer watch unrelated attribute churn.
  • Preserved attribute observation only where layout or winner/zoom state actually depends on class/style or geometry changes.

DOM Work and Caching

  • Added board/grid cache invalidation paths for:
    • tv-board-zoom
    • checkout-board-targets
    • cricket-highlighter
    • cricket-grid-fx
  • Limited cache resets to external DOM mutations, resize/orientation, visibility transitions, or node disconnection.
  • Removed an unnecessary overlay creation on the inactive clear path in checkout-board-targets.

Timers and Async Cleanup

  • Guarded late lazy-loader callbacks after cleanup in:
    • winner-fireworks
    • turn-points-count
  • Kept timeout, interval, and RAF cleanup explicit in feature teardown.
  • Gated optional polling work for hidden documents in:
    • single-bull-sound
    • triple-double-bull-hits

Notable Behavior Preserved

  • Feature config defaults are unchanged.
  • The checked-in dist/autodarts-xconfig.user.js bundle remains the canonical userscript artifact.
  • Runtime public API remains unchanged: window.__adXConfig surface and feature config keys are stable.

Residual Accepted Risks

  • The runtime still uses one observer per feature by design. This audit reduced unnecessary observer wakeups without introducing a shared observer multiplexer.
  • Some decorative features still observe broad DOM regions because Autodarts markup is not stable enough to pin them to a narrow host selector safely.
  • checkout-score-pulse keeps class-based observation because score focus can move through DOM class changes; it was left behavior-stable rather than aggressively coalesced.

Tests Added

  • duplicate websocket payload suppression
  • representative managed-mutation ignore path for checkout-board-targets
  • direct game-state-only scheduling path for remove-darts-notification
  • late async cleanup guard for turn-points-count
  • documentation coverage for the new runtime audit docs

Verification

Run after the code changes:

npm install
npm run build
npm test

Expected commit message:

perf(runtime): harden observers, listeners, and long-session stability

- document runtime entry points and audit findings
- remove duplicate game-state wakeups
- filter self-managed mutations and tighten observer scopes
- guard timers and async cleanup for long sessions
- add runtime stability regression tests