Distributed state · Sync
State Machine
When two computers disagree about what's true — and how UIs survive it.
Every modern app is two computers pretending to agree. The browser holds a copy of the state; the server holds the truth. These activities surface the contract — what happens when the browser updates first and asks later, what conflicts look like when two clients edit at once, why CRDTs and version vectors exist. The full-stack engineer's mental model lives here.
Optimistic updates · FE/BE contract · Rollback pathsOptimistic UI
Like a post with latency and failure-rate sliders. Optimistic mode updates instantly and rolls back on server failure; pessimistic mode waits. Burst five clicks and watch the trade between user-felt speed and rollback complexity play out in real time.
Teaches: Phase 4 · Backend Engineering