Function record_previous_version

src/upgrade.rs:701–714

Record the *currently running* binary's version in user config just before the binary is replaced. The new binary reads this on startup as `previous_version` and decides whether reinstall is required for the transition (e.g. minor/major bumps re-register agents to pick up new MCP tools or hook changes; patch bumps just update the field).

()

/// transition (e.g. minor/major bumps re-register agents to pick up new MCP
/// tools or hook changes; patch bumps just update the field).
fn record_previous_version() {
    let current = env!("CARGO_PKG_VERSION");
    let mut cfg = UserConfig::load();
    if cfg.previous_version == current {
        return;
    }
    cfg.previous_version = current.to_string();
    if !cfg.save() {
        eprintln!(
            "  \x1b[33mwarning:\x1b[0m could not record previous version; \
             run `tracedecay reinstall` manually if new tools aren't registered"
        );
    }
}

/// Returns the path the new binary was installed at, when known.
fn perform_upgrade(