System Design Twitter Course

The Undo Button — Point-in-Time Recovery via Event Replay

What We’re Building Today

• A replayFrom(isoTimestamp) function that rebuilds complete NEXUS state from any historical moment — replaying every INSERT, RELATE, and DELETE event up to that point into a fresh, fully queryable engine snapshot

• A debug HTTP endpoint GET /debug/feed?at=<iso> that returns follower counts, post content, and engagement totals exactly as they existed at any past timestamp

• An event-instrumented engine where every mutation is captured as an immutable log entry before touching in-memory state — making every state change auditable and reversible