Let Compact continue on another model or vendor

docs/operations.md

@@ -173,7 +173,7 @@ curl -H 'Tailscale-User-Login: you@example.com' -H 'Tailscale-User-Name: You' ht
 
 Images: `POST /api/blobs` takes a raw image body (type sniffed from the bytes, PNG, JPEG, GIF or WebP only, at most 5 MiB; `ImageTypes` and `MaxBlobBytes` in `internal/store/blob.go`) and returns its id; `GET /api/blobs/{id}` serves it. A message or session prompt may carry `images`, a list of blob ids (unknown ids are a 400); a message may then have empty text. byre reads each blob when the turn is sent and passes it before the text: to Claude as a base64 `image` content block (`claude.Session.Send`), to Codex as an `image` input with a `data:` URL (`codex.Session.Send`). The `user.message` event records the ids as `images`. In the composer, pasting or dropping an image adds a thumbnail with a × to remove it; images upload when the message is sent, and the transcript shows them on the user's message, each linking to the full image.
 
-Compaction is vendor-agnostic: `POST /api/sessions/{id}/compact` (the transcript's **Compact** button, always shown and enabled only while the task has an idle session) sends the agent `handoffPrompt` (`internal/agents/compact.go`) as a `byre` message, asking for a handoff covering the goal, decisions and why, current state, dead ends, open questions and files. That turn files no inbox summary and isn't bounced for questions. When it ends normally, its `turn.ended` carries `handoff: true`, the session is completed, and a new session on the same task and model starts with `handoffPreamble` plus the handoff as its first message (actor `byre`; its `user.message` carries `continuation: true`). The context meter tracks the new session. The request's `user.message` carries `handoff: true`, and from it the transcript puts the request and everything the agent does in that turn into one collapsed note reading "writing a handoff…", without streaming the agent's text; when the turn ends its summary becomes the `turn.ended` note, or "handoff not written" if the turn ended without one. The transcript never draws the new session's first message (`continuation: true`), so that note, which holds the handoff, is the only marker of the switch. If byre restarts during the handoff turn, the continuation is lost and the old session simply goes idle.
+Compaction is vendor-agnostic: `POST /api/sessions/{id}/compact` (the transcript's **Compact** button, always shown and enabled only while the task has an idle session) sends the agent `handoffPrompt` (`internal/agents/compact.go`) as a `byre` message, asking for a handoff covering the goal, decisions and why, current state, dead ends, open questions and files. That turn files no inbox summary and isn't bounced for questions. When it ends normally, its `turn.ended` carries `handoff: true`, the session is completed, and a new session on the same task starts with `handoffPreamble` plus the handoff as its first message (actor `byre`; its `user.message` carries `continuation: true`). The request's optional `model` (the button's long-press menu, `compact_task`'s `model`) picks the new session's model, on either vendor; without it the new session keeps the old one's. The old session still writes the handoff, so this can't get past a vendor that is rate-limited. The chosen model is held in memory (`Manager.handoffModel`) until the handoff turn ends. The context meter tracks the new session. The request's `user.message` carries `handoff: true`, and from it the transcript puts the request and everything the agent does in that turn into one collapsed note reading "writing a handoff…", without streaming the agent's text; when the turn ends its summary becomes the `turn.ended` note, or "handoff not written" if the turn ended without one. The transcript never draws the new session's first message (`continuation: true`), so that note, which holds the handoff, is the only marker of the switch. If byre restarts during the handoff turn, the continuation is lost and the old session simply goes idle.
 
 Task agents spawn parallel work as subtasks (see "Subtasks").