Read path and write path are different contracts

Before you start

• Requirements

  Estimates and APIs start from an agreed list of what the system must do.

  Open lesson

Why it matters

Publishing and opening home are different product promises. An author needs confirmation that a post will not disappear, while a follower needs a stable page even as newer posts arrive. Treating both as one generic feed call hides those guarantees. The post call must return after durability, and home must paginate without scanning every post in the system.

A user publishes a text post. A follower opens home and sees recent posts from people they follow.

For a text post, make POST /posts durable before 201, make POST /follows create the relationship, and make GET /home?cursor=p7 read one precomputed page so a new p10 cannot shift page two.

POST /posts inserts the text and returns 201 once that row is durable. POST /follows records the follower–author pair. Neither response waits for every reader’s home data; that work may finish within the agreed freshness window.

GET /home?cursor=p7 reads one newest-first page from the reader’s precomputed timeline and returns the next cursor. If p10 arrives before page two, starting after p7 still yields p6, p5, and p4. A numeric page offset would shift and repeat or skip an item.