Collaborative cursor sync
Design real-time multiplayer cursor and selection sync for a collaborative canvas/design tool (think Figma-style). 200 users in one file, each moving a cursor and dragging objects; everyone must see everyone else's cursor at ~60fps-feeling smoothness with sub-100ms perceived latency, over the public internet with varying RTTs. Object edits must converge; cursor positions are ephemeral.
What a strong answer looks like
Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts (data model, bottlenecks, consistency, failure modes) and name the trade-offs you are making.
Clarify5:30 left
Estimate5:30 planned
Design16:30 planned
Deep dive13:30 planned
Failure9:00 planned
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.