The most useful signal from a candidate shows up before a single line of code: the questions they ask about a vague task.
We hand people something small and deliberately under-specified, like adding refunds to an existing payment flow. The good ones stop to ask who is allowed to issue one, whether partial refunds count, and what happens if the original payment settled days ago. The ones who start building right away usually build something perfectly correct for a problem nobody actually asked about.
Real client work arrives exactly this under-specified, so we hire for the instinct to clarify first and build second. You probably have a question you wish someone had asked you before they started.