Function migrate_installed_agents

src/agents/mod.rs:1263–1270

Backfill `installed_agents` for users upgrading from older versions. Always scans every agent and adds any that have tracedecay configured (e.g. an `~/.claude.json` MCP server entry) but are absent from `installed_agents`. Without the additive scan, a user who installed agent A first and agent B later would have only A in the list, so `tracedecay reinstall` would silently skip B and its tool perm

(home: &Path, config: &mut crate::user_config::UserConfig)

/// `tracedecay reinstall` would silently skip B and its tool permissions
/// would never be refreshed when new tools ship.
pub fn migrate_installed_agents(home: &Path, config: &mut crate::user_config::UserConfig) {
    let additions = detect_missing_installed_agents(home, &config.installed_agents);
    if additions.is_empty() {
        return;
    }
    config.installed_agents.extend(additions);
    config.save();
}

#[cfg(test)]
#[allow(clippy::unwrap_used, clippy::expect_used)]