Function show_run_host 

pub fn show_run_host(run: &str, dir: Option<&Path>) -> Result<String>

Render the archived host context for the named run, resolved against dir (or test_support::runs_root() when dir is None). Loads sidecars under the run directory and returns the HostContext::format_human of the first sidecar that has a populated host field — every sidecar in a single run captures the same host, so first-wins is adequate.

Returns Err when:

• The run directory does not exist (actionable message names the expected root),
• The run directory exists but has no sidecar data (matches the compare_partitions error shape),
• Every sidecar carried host: None (older pre-enrichment runs won’t have the field).