Function looks_like_events_ts 

fn looks_like_events_ts(text: &str) -> Result<(), String>

Rejects a response body that is not the upstream module.

ureq already turns a 4xx/5xx into an error, so this is about the responses that arrive with status 200 and are still not the file: a captive portal or corporate proxy interstitial, a GitHub maintenance page, an HTML 404 from a CDN in front of raw.githubusercontent.com, or a body that was cut short before the interesting part. Left alone, all of those reach extract(), which reports the far less helpful “enum EventType not found”.