Function fetch_world 

pub fn fetch_world(
    resolver_base: &str,
    worlds_root: &Path,
    locator: &str,
) -> Result<TravelResult, String>

Resolve a Locator to a world (blocking — call on a background thread), in order of decreasing coupling:

1. the configured resolver/registry (Pixygon worlds + value-adds),
2. the host’s own .well-known/thread — decentralized, zero-registry: this is what lets anyone host a world on their domain with zero contact,
3. a local world.json (dev / offline authoring).