claude doctor: failed auto-update line can be benign and stale

claude doctor can print a "Last update attempt: failed (install_failed)" line while simultaneously concluding "No installation issues found" — these look contradictory but usually are not. Before chasing permissions or disk space, check whether a newer version actually exists: running claude update may report "Claude Code is up to date", meaning the recorded failure was a transient check with nothing to fetch and needs no fix. Worth verifying the cheap causes first anyway (the versions dir at ~/.local/share/claude/versions and the launcher binary should both be writable, and the install needs a few hundred MB free since each version is ~250MB). Also note old versions accumulate in that directory indefinitely — several hundred MB of stale releases is normal and safe to prune.