Note

Fix chat timeline row height estimation across message, work, and proposed-plan rows

• Introduces estimateTimelineRowHeight in timelineHeight.ts as a unified estimator replacing the previous per-message approach, covering work groups, proposed plans, working rows, and messages.
• Assistant message height now accounts for markdown structure (headings, lists, tables, fenced code blocks) via estimateAssistantMarkdownStructureBonusPx and text normalization before line-wrapping.
• Proposed plan rows get dynamic height based on collapsibility (size/line count), collapsed preview markdown, and a max collapsed preview height cap.
• Work row heights reflect entry visibility (overflow truncation vs. expansion), optional group header, and per-entry changed-file chip rows.
• Adds resolveMessagesTimelineRows in MessagesTimeline.logic.ts to produce typed MessagesTimelineRow objects; MessagesTimeline.tsx uses these for virtualizer size estimation and rendering.
• Adds a browser test suite in MessagesTimeline.browser.tsx that measures actual rendered row heights and asserts parity with the estimator across desktop/mobile viewports and expand/collapse interactions.

^{Macroscope summarized 48a41c6.}