Describe influencing without authority

Tell me about a time you disagreed with a senior engineer’s proposed design, but had no direct authority to change it. In your answer, use the STAR framework and include: (a) the concrete stakes, timeline, and measurable risks; (b) how you built alignment (stakeholder map, 1:1s, data/experiments used, decision docs); (c) the specific trade-offs you proposed and how you quantified impact (latency, reliability, cost); (d) how you handled conflict professionally when challenged in a live design review; (e) the final decision and measurable outcomes; and (f) what you would do differently if, months later, you found your alternative caused a regression under unexpected load.