[Bug] Update banner overlaps context banner on same line

**Bug Description**
Update-installed banner ("✔ Update installed · Restart to update") overlaps the context banner ("New task? /clear to save 118.4k tokens"). Both render on same row, text collides. macOS, Darwin 25.6.0, zsh.

This is an annoyance because when Claude auto-updates, old sessions no longer show uncached token cost.

**Environment Info**
- Platform: darwin
- Terminal: iTerm.app
- Version: 2.1.276
- Feedback ID: 74969875-8521-4e1a-8d33-52282a1a6cd8

**Errors**
```json
[]
```

Reproduce the issue in iTerm.app on macOS with an automatic update and the context banner visible, using the reported environment details as a starting point. Trace the terminal banner rendering area; done means the update-installed and context banners no longer overlap and the uncached token cost remains readable.

Written by the indexing model from the issue text.