Capital One Senior Lead AI Engineer Interview Experience — Four Power Day Rounds and a Virtual Credit Card Case

I did the four-round Senior Lead AI Engineer Power Day in late September. It felt all right overall. I guess poor performance on the VNC case was why I didn't pass.
Round 1 — AI Engineering / System Design
Design an Enterprise Agent Platform
The interviewer asked a series of AI / agent / platform / system-design questions that were within the scope of my preparation.
Round 2 — Technical Case: Virtual Credit Card
It was exactly the same question.
Round 3 — Behavioral
Scheduled for 60 minutes, but it actually ended after 40. Mostly standard behavioral questions, with an emphasis on leadership and ownership.
Round 4 — Coding + AI Fundamentals
First question: Sort Colors in place.
Second question: Debug a Python Flask Flask Cosine Similarity API. Given code and tests, find the bug and explain how to fix it.
AI Fundamentals covered guardrails, agent versus workflow, and latency.