Optimize loop performance

A hot loop in the rendering path is causing frame drops; optimize the loop that builds the virtual list by removing unnecessary allocations, hoisting invariant calculations, and using indexed access rather than repeated property lookups. Ensure the change keeps identical output and cut per-iteration work so the 1000-item render drops from 120ms to under 40ms.

Before I submit the loop change to reviewers, make the optimization clear and safe: show the current per-iteration cost and the proposed lowered cost, surface which expressions were hoisted or memoized, highlight any changes that affect mutation order, and flag tests that should be added to guard against subtle state bugs. Recommend ways to measure the improvement in CI.

I replaced a helper with a more expressive one and now the 500-item list render doubled in time; the hot spot seems to be a loop that allocates objects each iteration. I cannot tell whether eliminating allocations or changing the loop form will help more. Which quick experiment will give the clearest signal and how should I measure it?

I repeatedly ship code where naive loops cause regressions in medium-size datasets, and each fix takes an afternoon. Where am I most likely being sloppy — micro-allocation, property access, or algorithm choice — and what single coding habit change will prevent these loop problems in future reviews?