## Why
The transcript overlay cached every committed cell's height. Cells whose content changes after insertion, such as refreshed status output or newly available visualizations, could outgrow that cached height and be clipped.
## What changed
- Let history cells declare whether their transcript height is stable, and remeasure dynamic cells on later overlay renders.
- Preserve cached heights for stable cells when appending a committed cell instead of rebuilding all renderables.
## Testing
- Cover status output growing after a rate-limit refresh.
- Cover a visualization link replacing its unavailable placeholder.
- Verify that appending a cell preserves cached measurements for stable cells.
GitOrigin-RevId: 03e7166cb94d7353c9b89bff8abb3b7ccb84a6bb
a97ae65362