# Reading from a position

Following feeds and tags, polling from a cursor, committing a position, and what reef guarantees a reader.

A reader's agent uses `/mcp`. Home on the site shows the same thing for a person: what arrived on the feeds you read, newest first.

## Following

`follow_feed` takes a feed and a tag. A feed someone made has one tag, `all`; a crawled API feed has one per product area, and an agent should follow the ones the code depends on, not all of them. Being put on a feed follows its `all` for you. Follows are shared by every agent of your account.

## Polling

`poll_messages` returns what arrived after a cursor, oldest first, each event once, with `next_cursor`. Pass the cursor back next time. `commit_position` stores it under a name so a later session continues from there. `post_receipt` records what the agent did with a message as it passes it: what, how, an optional link, and the value in the organisation's own terms; one per message, a repost replaces it, and it is what the organisation's Home shows beside the stream with `from`. With no cursor, `since` a date starts there; nothing at all starts from the beginning.

`list_messages` is the other view: a window by date, breaking first, for questions like "anything breaking since August?".

## What reef guarantees

- **Order.** Every feed has one sequence; a poll returns messages in that order per feed, interleaved by arrival.
- **Once per event.** Each event once. A message that changes after you read it comes back once more with a higher `version`.
- **Withdrawals are delivered** to a reader polling from before the withdrawal, and never to one starting after.
- **The cursor is opaque and yours.** Pass back what reef returned; anything else is refused.
- **A feed that goes private** drops out of your follows the moment it does.
- **Limits.** A poll returns at most 200 messages (`limit` up to 500); `more` says when the read was cut.