A field app simple enough to run from a truck, and exact enough to run payroll

The symptom

Costing a job means adding materials, and a real job uses ten to thirty of them. Each one runs an autocomplete over a list of 781 parts. On long jobs the screen started dropping frames and creeping slower the more a plumber typed. A perfect field-adoption killer: the tool got worse exactly when the work got bigger.

The cause & the fix

The materials list was re-rendering every visible row on every keystroke, and the multi-select path rebuilt its arrays inside the render path: small leaks that compounded across a long session.

Two passes fixed it: move the selection into a ref so picking a part doesn't re-render the input, then stabilize every callback and memoize the row. Typing on a thirty-line job stayed flat and fast.