Streaming

The answer should appear as it's written. The AI SDK streams it to the browser, and on one happy path that's all there is to it.

The user closes the tab. Should the answer stop? If the server stops with the connection, the user comes back to half an answer, and the tools it ran are left half done.

The user reloads. The page loads the saved conversation. Where is the answer that's still being written?

The user sends another message. The first answer is still running. Two answers at once write into the same conversation in an order nobody chose.

An approval comes back later. After the click, the answer continues. Is that a new message, or the rest of the old one?

The server dies mid-sentence. Another server finishes the answer, but the browser was connected to the one that died.

What Latch does

The answer doesn't depend on the browser. Closing the tab ends the stream, not the run: the answer finishes on the server and is saved, ready when the user comes back.

One answer at a time per chat. A message sent while an answer is running gets 409 chat_busy with how long to wait, and nothing is saved, so the client can resend it.

With crash recovery on, every step is saved as it finishes. A reload shows the answer up to its last finished step; the rest appears when it's done. A server that took over a crashed answer saves to the same place.

A continued answer is the same message. After an approval, the stream continues the paused assistant message (same id) instead of starting a new one, so the UI fills in where it stopped.

In chat apps, streaming is real or not at all: Slack streams natively, other platforms get the finished answer. See Chat apps.