Skill: Octane performance audit

Use this to investigate performance regressions, benchmark results, scheduler/reconciler overhead, compiler output quality, or ecosystem binding perf.

Read first

• Benchmark README in the affected benchmarks/* directory
• packages/octane/src/runtime.ts comments for runtime-level changes
• Existing benchmark scripts in benchmarks/*/package.json and run.mjs

Workflow

1. Define target

   • Scenario: mount, update, keyed reorder, context, effects, Suspense, hydration, SSR, binding package.
   • Metric: runtime duration, allocations, DOM operations, bundle size, compiler output size, benchmark score.
   • Baseline: current main, previous commit, React, Solid/Ripple comparison, or documented expectation.
   • Semantic control: the output, identity, ordering, or lifecycle result that proves both candidates perform the same work.

2. Choose harness

   • Existing benchmarks: benchmarks/news, js-framework, recursive-context, signal-favoring, dbmon.
   • Micro regression: focused Vitest with counters/logging.
   • Compiler output: inspect emitted JS from compile.js/Vite transform.
   • Browser-only perf: use Playwright or benchmark harness if available.

3. Run baseline and candidate

   • Warm up.
   • Run multiple iterations.
   • Record environment and command.
   • Avoid mixing dependency install/build changes with code changes.
   • Use the same commit inputs, runner options, and machine state. Do not compare a quick smoke result with a full result.
   • Treat a delta inside observed variance as inconclusive. Prefer ratio guards and deterministic counters when wall-clock noise is larger than the claim.

4. Diagnose

   • Runtime hot paths: scheduler queues, effect flushing, keyed reconciliation, event delegation, context propagation, refs.
   • Compiler hot paths: unnecessary deopts, over-broad dynamic regions, missed folding, slot churn, repeated closures.
   • Binding hot paths: excessive subscriptions, selector equality failures, layout-effect loops.

5. Patch or report

   • Prefer measurable changes with a regression test/benchmark note.
   • Preserve correctness over micro-optimizations.
   • Document tradeoffs and residual risk.

6. Challenge the conclusion

   • Inspect whether work was shifted to startup, compilation, hydration, garbage collection, or a less visible branch rather than removed.
   • Check allocation lifetime and invalidation for new caches or memoization.
   • Attempt a workload that should make the proposed improvement disappear; if it does not, look for a harness or measurement error.
   • Re-run the final candidate after self-review changes. Never report a stale intermediate measurement as the final result.

Report template

## Performance audit
- Target: ...
- Baseline command/result: ...
- Candidate command/result: ...
- Delta: ...

## Findings
- ...

## Recommendation
- ...

## Validation
- ...

## Confidence and residual risk
- Noise/variance: ...
- Modes not measured: ...
- Alternative explanation considered: ...

Common pitfalls

• jsdom is poor for layout/paint measurements.
• Differential innerHTML tests prove correctness, not performance.
• React and Octane may perform different physical DOM move sets while producing identical final DOM.
• Compiler output changes can shift runtime cost; inspect both layers.