| Q281 | System design frame | Clarify users, workflows, data, state, APIs, rendering, performance, security, observability, and rollout. |
| Q282 | Requirements | Define P0/P1 scope, assumptions, non-goals, scale, constraints, and sensitive data before designing. |
| Q283 | State model | Separate server, URL, form, local, draft, optimistic, derived, realtime, and persistent client state. |
| Q284-Q285 | Contracts and scale | Design API contracts from workflows and place responsibilities across client, server, edge, and background jobs. |