# Market data

`/market-data` uses client subscription frames and does not support `since`.

1. Connect and send `{"type":"subscribe","markets":[...]}`.
2. Receive one `book_snapshot` for each newly subscribed market and replace the local book with it.
3. Apply each `book_diff` and `trade` in contiguous per-market `md_seq` order. A price level with `qty = 0` is deleted.
4. On an `md_seq` gap, request a fresh snapshot by subscribing with `force_snapshot: true`, then rebuild from that snapshot.
5. After reconnecting, subscribe again; the server sends fresh snapshots.

Unlike resumable-stream `seq`, market-data `md_seq` is dense per market on data frames. Heartbeats do not advance it. The server can also send periodic snapshots; apply them in the same way as the initial snapshot.