[Bug] Auto-update fails to update symlink to latest downloaded version

Bug Description
Title: Auto-update downloads new versions but fails to update symlink

Description:
Auto-update mechanism downloads new versions to ~/.local/share/claude/versions/ but does not update the symlink at ~/.local/bin/claude, leaving the CLI stuck on an old version.

Expected behavior:
When a new version is downloaded, the symlink should be updated to point to the latest version.

Actual behavior:

• New versions are downloaded (2.1.5, 2.1.9 were present in versions directory)
• Symlink remains pointing to old version (2.1.2)
• claude update reports "Claude Code is up to date" despite newer versions being available
• claude --version shows old version

Environment:

• macOS (Darwin 25.0.0)
• Native installation at ~/.local/bin/claude
• autoUpdatesChannel: "latest" configured
• DISABLE_AUTOUPDATER not set

Investigation:
$ ls ~/.local/share/claude/versions/
2.1.2 2.1.5 2.1.9 # 2.1.9 already downloaded

$ ls -la ~/.local/bin/claude
claude -> ~/.local/share/claude/versions/2.1.2 # Still pointing to old version

$ claude update
Claude Code is up to date (2.1.2) # Incorrectly reports as up to date

Workaround:
Manually updating symlink: ln -sf ~/.local/share/claude/versions/2.1.9 ~/.local/bin/claude

Symlink was reverted automatically after manual fix.

• Fixed symlink to 2.1.9 manually
• After some time, symlink was reverted to 2.1.2
• Timestamp shows active process is overwriting the symlink

This indicates something is actively reverting the symlink to an old version, not just failing to update it.

Environment Info

• Platform: darwin
• Terminal: vscode
• Version: 2.1.2
• Feedback ID: 0a686907-3ca1-4ff4-b1d6-960995959283