0004 Reattach by byte offset, with a full redraw as the fallback

Context

After a disconnect, the user’s terminal still shows the session’s earlier output, in its native scrollback. Sending the whole history again would duplicate it. Sending nothing would lose the output printed while away.

Options

1. Always redraw the whole screen
2. Replay from the client’s last byte offset when it is still in the holder’s ring; otherwise redraw
3. Clear the local scrollback on every attach

Decision

Option 2. The holder keeps the last 8 MiB of output, with absolute offsets. A client that reattaches in the same terminal sends its offset and gets exactly the bytes it missed, so scrollback continues with no gap and no duplicate. A new client, or an offset that fell out of the ring, gets a full redraw. Replayed bytes have terminal queries removed, so the local terminal never answers a stale question. A setting can clear local scrollback on a full redraw.

Consequences

• Good, because sleep and network changes cost nothing visible.
• Good, because notifications sent while away still arrive.
• Bad, because the client must remember terminal modes and restore them before replaying.