UX: Notify user when a newer version is available and offer in-session restart

Problem

When a new version of Claude Code is installed on disk while a session is already running, there is no notification. The running session silently continues on the old version. The user only discovers the mismatch by manually comparing the terminal header version against the output of claude update.

Example: Session started on v2.1.72. Binary updated to v2.1.76 on disk. Running claude update reports 'Claude Code is up to date (2.1.76)' — but the terminal header still shows v2.1.72 with no explanation.

Requested behavior

1. At startup (or when claude update is run), detect if the on-disk binary version differs from the running process version
2. Show a non-intrusive banner: 'v2.1.76 is available — exit and relaunch to apply'
3. Ideally offer a /restart command to re-exec the new binary cleanly

Why it matters

• Users on long sessions unknowingly operate on stale versions
• Bug fixes and new features in the updated binary are silently unavailable
• The current behavior causes confusion — claude update says 'up to date' but the header shows an older version

Prior art

This mirrors standard patterns in: VS Code (extension update notifications), gh, brew, npm global packages. Zero network cost — just compare running process version against installed binary path.

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Submitted via Claude Code in-session — TAMTS project, Ubuntu WSL2, 2026-03-16