Let Compact continue on another model or vendor

docs/macos.md

@@ -93,7 +93,7 @@ Closing the window leaves the app running with its store and streams (`applicati
 
 ## Views
 
-- **Transcript and Lead.** `TranscriptBuilder` is a pure function from events to a list of rows: user and agent messages, consecutive tool calls folded into one group with its summary ("Read file ×3"), subagents nested with their status, pending tool calls and running subagents (background ones included after the turn ends) outlined in the accent colour with a 0.6s fade, thinking, the byre prompt collapsed, held turns, `NO_REPLY` turns folded away, handoffs, snapshot rows with changes, fork and review, and notes for the other event kinds. It is incremental: a new batch extends the existing rows. The view is a `ScrollView` with a plain `VStack`, stuck to the bottom unless the user has scrolled more than 80 points up. The stack isn't lazy because a `LazyVStack` estimates the height of rows it hasn't shown yet and corrects it when they scroll into view, without moving the scroll offset, so scrolling up through rows not yet shown jumped by each correction; SwiftUI can't move the offset mid-scroll without stopping its momentum. While the user is scrolling (`onScrollPhaseChange`), content height changes only update whether it is stuck and never pull it back to the bottom. The lead pages back when the view comes within one screen of the top: the fetched page is held while the scroll phase is scrolling and inserted once it is idle (`ChatModel.older`, `prependOlder`), and the next geometry change moves the offset down by the height added, so the rows on screen stay put; a page that adds no rows (all folded `NO_REPLY` turns) fetches the next one at once. Each Markdown text run's `NSTextView` measures its height with one TextKit stack kept in its coordinator, and a repeat measurement at the same width and text returns the stored size. Pending sends show at the end until the server echoes them. A turn summary counts as read when its row is on screen and the app is active (`markSummaryRead`). The head carries Compact (with its context-usage fill), Sync from main, Merge and Discard.
+- **Transcript and Lead.** `TranscriptBuilder` is a pure function from events to a list of rows: user and agent messages, consecutive tool calls folded into one group with its summary ("Read file ×3"), subagents nested with their status, pending tool calls and running subagents (background ones included after the turn ends) outlined in the accent colour with a 0.6s fade, thinking, the byre prompt collapsed, held turns, `NO_REPLY` turns folded away, handoffs, snapshot rows with changes, fork and review, and notes for the other event kinds. It is incremental: a new batch extends the existing rows. The view is a `ScrollView` with a plain `VStack`, stuck to the bottom unless the user has scrolled more than 80 points up. The stack isn't lazy because a `LazyVStack` estimates the height of rows it hasn't shown yet and corrects it when they scroll into view, without moving the scroll offset, so scrolling up through rows not yet shown jumped by each correction; SwiftUI can't move the offset mid-scroll without stopping its momentum. While the user is scrolling (`onScrollPhaseChange`), content height changes only update whether it is stuck and never pull it back to the bottom. The lead pages back when the view comes within one screen of the top: the fetched page is held while the scroll phase is scrolling and inserted once it is idle (`ChatModel.older`, `prependOlder`), and the next geometry change moves the offset down by the height added, so the rows on screen stay put; a page that adds no rows (all folded `NO_REPLY` turns) fetches the next one at once. Each Markdown text run's `NSTextView` measures its height with one TextKit stack kept in its coordinator, and a repeat measurement at the same width and text returns the stored size. Pending sends show at the end until the server echoes them. A turn summary counts as read when its row is on screen and the app is active (`markSummaryRead`). The head carries Compact (with its context-usage fill; a long press opens a menu of models to continue on), Sync from main, Merge and Discard.
 - **Composer.** A `TextEditor`, with paste and drop handled as in "Gaps in SwiftUI". Text, the model menu (filtered to the live session's vendor), Interrupt and Send. Enter sends, Shift-Enter adds a newline, and Enter during IME composition does neither. Pasted or dropped PNG, JPEG, GIF and WebP images become thumbnails with ×, uploaded to `POST /api/blobs` on send; any other image `NSBitmapImageRep` decodes, such as TIFF, is converted to PNG first, its size checked after conversion. A failed send puts the text and images back and shows the error.
 - **Inbox.** The selected task's oldest open item, rendered from its Markdown context with each choice's marker replaced by a clickable block (pick-one, sends at once) or checkbox (pick-any, with Submit), the "recommended" tag, image-choice grids, attachments, Let the agent decide, Other… and, for errors, Reply… and Dismiss. Arrow keys move between choices. A 409 shows its error. The Changes summary line sits above it.
 - **Changes, Files, Reviews, Workflow, Project, Status, Settings.** Including the pinned-snapshot stepper, open-diff memory, per-task place in Files, finding diffs with Fix and Ignore, nested subtasks, TODO Start and Discuss, rate-limit pace bars and lead notes. The Workflow tab draws its stage graph natively from the `WorkflowRun` (stages as boxes coloured by state, `after` as edges, laid out top to bottom by depth) with the layout and drawing code from "Diagrams", fed from the run's data rather than Mermaid text.

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").