Stop the macOS transcript jumping while scrolling

docs/macos.md

@@ -101,7 +101,7 @@ Closing the window leaves the app running with its store and streams (`applicati
 
 Each view does what its TypeScript counterpart does, with the same text, refresh triggers and empty states.
 
-- **Transcript and Lead.** `TranscriptBuilder` ports `appendEvents` and `renderEvent` from `task.ts` as 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 each event kind the web client draws. It is incremental: a new batch extends the existing rows. The view is a `ScrollView` with a `LazyVStack`, stuck to the bottom unless the user has scrolled more than 80 points up, with pending sends shown 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, with the same enabling rules and tooltips.
+- **Transcript and Lead.** `TranscriptBuilder` ports `appendEvents` and `renderEvent` from `task.ts` as 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 each event kind the web client draws. It is incremental: a new batch extends the existing rows. The view is a `ScrollView` with a `LazyVStack`, stuck to the bottom unless the user has scrolled more than 80 points up. While the user is scrolling (`onScrollPhaseChange`), content height changes from rows the `LazyVStack` lays out late only update whether it is stuck and never pull it back to the bottom. 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, with the same enabling rules and tooltips.
 - **Composer.** A `TextEditor`, with paste and drop handled as in "Gaps in SwiftUI". Text, the model menu (filtered by vendor as in `modelSelect`), 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 up to the web client's limit become thumbnails with ×, uploaded to `POST /api/blobs` on send. 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 as in the browser. The Changes summary line sits above it.
 - **Changes, Files, Reviews, Workflow, Project, Status, Settings.** Ports of their files, 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.