Function prune_old_cache_entries

rust/src/lib.rs:1757–1783

Removes cached driver and browser binaries whose `last_used` timestamp (tracked in the `cached_assets` section of the metadata) is older than `ttl_days` days. `cached_assets` is intentionally separate from the TTL-based `drivers`/`browsers` entries so that usage history survives beyond the short version-discovery TTL (default: 1 hour). This prevents binaries from escaping pruning just because the

(log: &Logger, cache_path: &str, ttl_days: u64)

/// This prevents binaries from escaping pruning just because their metadata entry was already
/// flushed by a routine write for a different driver or browser.
pub fn prune_old_cache_entries(log: &Logger, cache_path: &str, ttl_days: u64) {
    let cache = Path::new(cache_path);
    if !cache.exists() {
        return;
    }
    let cache_path_buf = cache.to_path_buf();
    let mut metadata = get_metadata(log, &Some(cache_path_buf.clone()));
    let cutoff = now_unix_timestamp().saturating_sub(ttl_days * 24 * 3600);

    let old_assets: Vec<(String, String)> = metadata
        .cached_assets
        .iter()
        .filter(|a| a.last_used < cutoff)
        .map(|a| (a.asset_name.clone(), a.asset_version.clone()))
        .collect();

    if old_assets.is_empty() {
        return;
    }

    for (name, version) in &old_assets {
        delete_cached_asset(log, cache, name, version);
    }

    metadata.cached_assets.retain(|a| a.last_used >= cutoff);
    write_metadata(&metadata, log, Some(cache_path_buf));
}

fn delete_cached_asset(log: &Logger, cache: &Path, asset_name: &str, asset_version: &str) {
    let asset_dir = cache.join(asset_name);