Performance Pass UI

Skill: frontend/performance-pass-ui

Purpose

Improve UI performance by removing obvious regressions and hotspots:

• unnecessary rerenders
• expensive derived computations on render
• unbounded lists or heavy DOM
• avoidable bundle bloat and lazy-load misses

This is a focused pass. It should not change user-facing behavior.

Inputs

• Target UI surface (route/component)
• Reported symptom (slow render, jank, laggy typing, long TTI) if known
• Repo profile (preferred): <repo>/REPO_PROFILE.json (framework/tooling/commands)
• Existing instrumentation (React DevTools Profiler, performance marks, logs) if present

Outputs

• Minimal code changes improving performance
• Notes in code comments where tradeoffs exist (why memoization, why virtualization, etc.)
• Optional: small measurement note in PR summary (before/after) if measurement is available

Non-goals

• Visual redesign
• Refactoring purely for style
• Introducing new dependencies unless repo standard
• Premature micro-optimizations without evidence

Workflow

1. Establish baseline:
   • reproduce issue or identify likely hot path
   • prefer measurable evidence (profiler, devtools, timing marks)
2. Identify top offenders:
   • rerender cascades (props identity churn)
   • heavy computations in render
   • large lists without virtualization
   • excessive re-fetch or revalidation loops
3. Apply smallest effective fix:
   • memoize derived values (useMemo) only when computation is non-trivial
   • stabilize callbacks (useCallback) only when it prevents churn
   • split components to reduce rerender surface
   • add list virtualization if large lists
   • add lazy loading for heavy routes/components if repo uses it
4. Verify behavior unchanged:
   • same UI output and interaction
5. Run validations from profile.

Checks

• No user-visible behavior change (same UI states and interactions)
• Typecheck/lint pass if configured
• Performance improvement is plausible and localized:
  • fewer renders in hot path OR
  • reduced work per render OR
  • reduced payload/deferral of heavy components
• No new infinite loops (effects, memo deps, query invalidations)

Failure modes

• No evidence of perf issue → add minimal measurement first or decline changes.
• Memoization causes stale UI → fix dependencies or remove optimization.
• Optimization increases complexity too much → revert and propose a safer alternative.
• Large list performance issues → recommend virtualization; if not allowed, limit rendered rows.

Telemetry

Log:

• skill: frontend/performance-pass-ui
• target: <route/component>
• techniques: memo | split | virtualization | lazy-load | effect-fix | other
• files_touched
• outcome: success | partial | blocked